Considering the ‘Green Great Wall’ project and future climate change, the vegetation in the Northwest Hetao

Plain (NWHP) of China is expected to undergo considerable changes. In this study, the climatic response to prescribed

changes in vegetation is investigated using the Weather Research and Forecasting model. When the vegetation is changed

from ‘bare or sparsely vegetated’ category to ‘grassland’ in the NWHP, the climate shows both local and remote responses.

Locally, the temperature increases in the winter but decreases in the summer. The precipitation level increases substantially

in the summer while increases slightly in the winter, which is mainly caused by the increase in the amount of water-vapour

and circulation adjustment. Additionally, atmospheric circulation anomalies also lead to remote circulation responses,

including a decrease in precipitation over Central North China and an increase in precipitation over Central and South

China. The results of this study bring to light the local and remote climatic responses to changes in vegetation in the

NWHP using a state-of-the-art regional climate model.

利用WRF(Weather Research and Forecasting)模式, 进行了我国东北地区冬季降雪的高分辨率数值模拟, 评估了WRF 模式对季节降雪的模拟能力, 并探讨了模式水平分辨率和物理

过程参数化方案对降雪模拟的影响. 结果显示WRF 模式可以合理地模拟冬季气温和降水的空间分布, 模拟结果和观测吻合较好. 该模式可以合理地模拟东北地区季节降雪的空间分布和时间演变, 显示了该模式较强的模拟性能. 水平分辨率和物理过程参数化方案对降雪模拟有重要影响, 高分辨率模拟结果更接近观测; 相对于积云对流参数化方案, 模式对陆面过程和微物理过程参数化方案更加敏感.

Effective statistical downscaling schemes based on singular value decomposition (SVD) for boreal autumn

(September-October-November) precipitation over China were developed. It was found that rainfall over China is closely

tied to large-scale atmospheric and oceanic circulation over specific regions. The general circulation models (GCMs),

which are from DEMETER project (Development of a European Multi-model Ensemble System for Seasonal to Interannual

Prediction), perform reasonably well in simulating the mean states of geopotential height at 500 hPa (GH5) during autumns

from 1960 to 2001. Consequently, the variable GH5 over East Asia from DEMETER GCMs was used as one predictor for

downscaling. Meanwhile, another predictor is the preceding sea surface temperature (SST) signal from observed data over

the tropical Pacific. The downscaling results involving only the GH5 predictor (GH5 scheme) or both the GH5 and SST

predictors (GH5+SST scheme) were discussed and compared in this study. Downscaling based on two kinds of schemes

showed considerable improvement compared with original DEMETER GCMs in predicting regional autumn precipitation.

In particular, downscaling predictions based on the GH5+SST scheme showed lower root mean square errors than those

based on the GH5 scheme, especially for the precipitation anomaly pattern of the El Ni˜no event in 1997 and the La Ni˜na

event in 1998.

探讨了WRF模式在风电场的风速或者功率预报中应用的可行性, 主要研究和评估了WRF模式对地处东亚季风区及海陆交界的江苏如东地区夏季和冬季风速的短期预报效能。研究发现WRF模式可以比较好地预报如东站冬季的风速, 24 h预报的风速时间序列和观测资料的相关系数可以达到0.61, 通过置信度99%的检验, 48 h和72 h的预报与观测风速相关系数分别为0.54和0.47, 也能通过置信度99%的检验;相对而言, 模式对夏季风速的预报则要差一些, 24 h的相关系数有0.59, 48 h和72 h的相关系数只有0.47和0.30, 但仍能通过置信度99%的检验。在量值上, 模式预报的风速比观测值都略偏大一些。而江苏南通市预报结果显示, 模式的预报效能要比如东稍高一些, 和如东类似, 模式对该地冬季的预报要好于对夏季风速的预报。从更大尺度范围的分析也表明, 模式对不同地区预报的准确度是不一样的, 对海面以及海陆交界的海岸预报精度要高一些, 在平坦的内陆地区预报也比较好, 但在山区预报效能则较差。总体说来, WRF能胜任风速短期预报, 值得进一步研究和应用。

链接http://www.dqkxqk.ac.cn/qhhj/ch/reader/view_abstract.aspx?file_no=20130201&flag=1

引用:汪君,王会军.2013.WRF模式对江苏如东地区风速预报的检验分析[J].气候与环境研究,18(2):145-155,doi:10.3878/j.issn.1006-9585.2013.11152.

Citation:WANG Jun and WANG Huijun.2013.Forecasting of Wind Speed in Rudong, Jiangsu Province, by the WRF Model[J].Climatic and Environmental Research(in Chinese),18(2):145-155,doi:10.3878/j.issn.1006-9585.2013.11152.

大雪和暴雪是东北冬半年(前一年11 月~次年3 月)发生主要的极端天气和气候事件, 是我国当前主要的气象灾害之一. 此前的研究主要集中于东北大雪和暴雪天气个例的成因和天气预测, 对其气候预测研究甚少, 因为大雪-暴雪年际变率非常大, 气候规律复杂, 同时动力模式对中高纬气候预测能力较低, 预测非常困难. 本文基于东北冬半年大雪和暴雪日数的年际增量的气候变化规律及其影响系统, 尝试开展东北地区大雪-暴雪日数的气候预测. 本文选取4 个具有物理意义的预测因子, 包括东北北部地区前期9 月土壤湿度异常的陆面过程的影响、表示冬季西北太平洋海气过程的预测因子、前期夏季马斯克林高压和前一年前期冬半年东北暖湿气流, 研制东北地区冬半年大雪-暴雪日数气候预测模型, 并对预测模型进行1963~2011 年(48 年)独立样本交叉检验和1983~2010 年(28 年)独立样本回报检验, 两种检验结果均表明该预测模型对东北大雪-暴雪日的年际增量及其距平百分率具有较高的预测能力. 48 年的交叉检验中, 年际增量(距平百分率)相关系数是0.86(0.77), 均超过0.01 的显著性水平. 距平百分率绝对误差是16%, 平均均方根误差是20%. 本研究结果为东北大雪-暴雪日数的气候预测研究提供一个有效预测方法和预测模型, 值得在预测实际业务中试验应用.

The East Asian summer (June–July–August) monsoon (EASM) is typically thought to have been stronger during interglacial periods based on spatially sparse proxy data. On a large scale, however,whether this viewis true and if so, its underlying dynamic mechanisms remain unclear. Using all pertinent experiments within the Paleoclimate Modeling Intercomparison Project (PMIP), here we present an analysis of the EASM during the mid-Holocene, 6000 years ago. Supporting the paleodata, the mid-Holocene EASM, as measured by regionally averaged meridional wind at 850 hPa, became stronger than the baseline period in 27 out of 28 PMIP models with a demonstrable ability to simulate the modern EASM climatology. On average, the EASM strengthened by 32% across all themodels and by a largermagnitude in 23 coupledmodels (35%) than in five atmosphericmodels (20%). It is proposed that an enhanced land–sea thermal contrast, and hence sea level pressure gradient, between the East Asian continent and adjacent oceans as a result of orbital forcingwas responsible for the EASM strengthening during the mid-Holocene.

Forty-two climate models participating in the coupled Model Intercomparison Project Phases 3 and 5 were first evaluated in terms of their ability to simulate the present climatology of the East Asian winter (December–February) and summer (June–August) monsoons. The East Asian winter and summer monsoon changes over the 21st century were then projected using the results of 31 and 29 reliable climate models under the Special Report on Emissions Scenarios (SRES) mid-range A1B scenario or the Representative Concentration Pathways (RCP) mid-low-range RCP4.5 scenario, respectively. Results showed that the East Asian winter monsoon changes little over time as a whole relative to the reference period 1980–1999. Regionally, it weakens (strengthens) north (south) of about 25°N in East Asia, which results from atmospheric circulation changes over the western North Pacific and Northeast Asia owing to the weakening and northward shift of the Aleutian Low, and from decreased north-west-southeast thermal and sea level pressure differences across Northeast Asia. In summer, monsoon strengthens slightly in East China over the 21st century as a consequence of an increased land-sea thermal contrast between the East Asian continent and the adjacent western North Pacific and South China Sea.

This study investigates the impact of global

warming on drought/flood patterns in China at the end of

the 21st century based on the simulations of 22 global

climate models and a regional climate model (RegCM3)

under the SRES (Special Report on Emissions Scenarios)

A1B scenario. The standardized precipitation index (SPI),

which has well performance in monitoring the drought/

flood characteristics (in terms of their intensity, duration,

and spatial extent) in China, is used in this study. The

projected results of 22 coupled models and the RegCM3

simulation are consistent. These models project a decrease

in the frequency of droughts in most parts of northern

China and a slight increase in the frequency in some parts

of southern China. Considering China as a whole, the

spatial extents of droughts are projected to be significantly

reduced. In contrast, future flood events over most

parts of China are projected to occur more frequently with

stronger intensity and longer duration than those prevalent

currently. Additionally, the spatial extents of flood events

are projected to significantly increase.

Future changes in East Asian summer monsoon (EASM) precipitation climatology, frequency, and intensity are analyzed using historical climate simulations and future climate simulations under the RCP4.5 scenario using the World Climate Research Programme’s (WCRP) Couple Model Intercomparison Project 5 (CMIP5) multi-model dataset. The model reproducibility is evaluated, and well performance in the present-day climate simulation can be obtained by most of the studied models. However, underestimation is obvious over the East Asian region for precipitation climatology and precipitation intensity, and overestimation is observed for precipitation frequency. The overestimation of precipitation frequency is mainly due to the large positive bias of the light-precipitation (precipitation < 10 mm/day) days, and the underestimation of precipitation intensity is mainly caused by the negative bias of the intense-precipitation (precipitation > 10 mm/day) intensity. For the future climate simulations, simple multi-model ensemble (MME) averages using all of the models show increases of precipitation and its intensity over almost all of East Asia, while the precipitation frequency is projected to decrease over eastern China and around Japan and increase in other regions. When the weighted MME is considered, no large difference can be observed compared with the simple MME. For the MME using the six best models that have good performance in simulating the present-day climate, the future climate changes over East Asia are very similar to those predicted using all of the models. Further analysis shows that the frequency and intensity of intense precipitation events are also projected to significantly increase over East Asia. Increases in precipitation frequency and intensity are the main contributors to increases in precipitation, and the contribution of frequency increases (contributed by 40.8% in the near future and by 58.9% by the end of the 21st century) is much larger than that of intensity increases (contributed by 29.9% in the near future and by 30.1% by the end of the 21st century). This finding also implies an increased risk of intense precipitation events over the East Asian region under global warming scenario. These results regarding future climate simulations show much greater reliability than those using CMIP3 simulations.

Based on a 153-year (1948–2100) transient simulation of East Asian climate performed by a high resolution regional climate model (RegCM3) under the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenarios (SRES) A1B scenario, the potential future changes in mean and extreme climates over China in association with a global warming of 2°C with respect to pre-industrial times are assessed in this study. Results show that an nual temperature rises over the whole of China, with a greater magnitude of around 0.6°C compared to the global mean increase, at the time of a 2°C global warming. Large-scale surface warming gets stronger towards the high latitudes and on the Qinghai-Tibetan Plateau, while it is similar in magnitude but somewhat different in spatial pattern between seasons. Annual precipitation increases by 5.2%, and seasonal precipitation increases by 4.2%–8.5% with respect to the 1986–2005 climatology. At the large scale, apart from in boreal winter when precipitation increases in northern China but decreases in southern China, annual and seasonal precipitation increases in western and southeastern China but decreases over the rest of the country. Nationwide extreme warm (cold) temperature events increase (decrease). With respect to the 1986–2005 climatology, the country-averaged annual extreme precipitation events R5d, SDII, R95T, and R10 increase by 5.1 mm, 0.28 mm d–1, 6.6%, and 0.4 d respectively, and CDD decreases by 0.5 d. There is a large spatial variability in R10 and CDD changes.

We attempt to apply year-to-year increment

prediction to develop an effective statistical downscaling

scheme for summer (JJA, June–July–August) rainfall prediction

at the station-to-station scale in Southeastern China

(SEC). The year-to-year increment in a variable was

defined as the difference between the current year and the

previous year. This difference is related to the quasibiennial

oscillation in interannual variations in precipitation.

Three predictors from observations and six from three

general circulation models (GCMs) outputs of the development

of a European multi-model ensemble system for

seasonal to interannual prediction (DEMETER) project

were used to establish this downscaling model. The independent

sample test and the cross-validation test show that

the downscaling scheme yields better predicted skill for

summer precipitation at most stations over SEC than the

original DEMETER GCM outputs, with greater temporal

correlation coefficients and spatial anomaly correlation

coefficients, as well as lower root-mean-square errors.

The aim of this paper is to use a statistical downscaling model to predict spring precipitation over China based on a large-scale circulation simulation using DEMETER (Development of a European Multi-model Ensemble System for Seasonal to Interannual Prediction) General Circulation Models (GCMs) from 1960-2001. An SVD (singular value decomposition) regression analysis was performed to establish the link between the spring precipitation and the large-scale variables, particularly for the geopotential height at 500 hPa and the sea level pressure. The DEMETER GCM predictors were determined on the basis of their agreement with the reanalysis data for specific domains. This downscaling scheme significantly improved the predictability compared with the raw DEMETER GCM output for both the independent hindcast test and the cross validation test. For the independent hindcast test, multi-year average spatial correlation coefficients (CCs) increased by at least approximately 30% compared with the DEMETER GCMs’ precipitation output. Additionally, the root mean square errors (RMSEs) decreased more than 35% compared with the raw DEMETER GCM output. For the cross validation test, the spatial CCs increased to greater than 0.9 for most of the individual years, and the temporal CCs increased to greater than 0.3 (95% confidence level) for most regions in China from 1960 to 2001. The RMSEs decreased significantly compared with the raw output. Furthermore, the preceding predictor, the Arctic Oscillation, increased the predicted skill of the downscaling scheme during the spring of 1963.

East Asian summer monsoon (EASM) prediction is difficult because of the summer monsoon’s weak and unstable linkage with El Niño-Southern Oscillation (ENSO) interdecadal variability, and complicated association with high latitude processes. Two statistical prediction schemes were developed to include the interannual increment approach (Fan et al., 2008) to improve the seasonal prediction of the EASM strength. The schemes were applied to three models (i.e., CNRM, UKMO and ECMWF) and the Multi-models Ensemble (MME) from the Development of a European Multi-model Ensemble System for Seasonal to Interannual Prediction (DEMETER) results for 1961-2001. The inability of the three dynamical models to reproduce the weakened East Asian monsoon at the end of the 1970s leads to low prediction ability for the interannual variability of the EASM. Therefore, the interannual increment prediction approach was applied to overcome this issue. Scheme-I contained the EASM in the form of year-to-year increments as a predictor that is derived from the direct outputs of the models. Scheme-II contained two predictors: both the EASM and also the western North Pacific circulation in the form of year-to-year increments. Both the cross-validation test and the independent hindcast experiments showed that the two prediction schemes have a much better prediction ability for the EASM than the original scheme. This study provides an efficient approach for predicting the EASM.

The performance of climate models in simulating the linkage of the spring Hadley circulation (HC) to the vertical zonal wind shear and atmospheric divergence in the lower and upper troposphere, which are related to the tropical cyclone frequency over the western North Pacific (WNPTCF) during June–September (JJAS), is evaluated on the basis of the 20th century climate simulations (20C3M). It is found that four models can simultaneously reproduce the pattern revealed in the observation, with the spring HC in the Northern Hemisphere being positively correlated to the vertical zonal wind shear in the major tropical cyclone (TC) genesis region and negatively (positively) correlated to the atmospheric divergence in the upper (lower) troposphere over the western North Pacific (WNP) in the following JJAS. These four models are further used to project their relationship in the late 21st century under the A1B scenario. The results show that the association of spring HC with the vertical zonal wind shear and the upper- and lower-tropospheric divergence over the WNP will weaken in the late 21st century, thereby resulting in a weak relationship between the spring HC and the JJAS WNPTCF.

It is indicated by the observation that spring Hadley circulation is tightly linked to East Asian summer circulations and precipitation on the interannual timescale. Whether does such a relationship as in the observation tend to change under the background of global warming in the future? To answer this question, five climate models （GFDL_CM2_0，GFDL_CM2_1，IAP_FGOALS_1.0g，NCAR_CCSM，UKMO_HADCM3）, which can well reproduce the observed interannual variability of spring Hadley circulation in the Northern Hemisphere and its linkage to East Asian summer atmospheric circulations and precipitation are firstly chosen based on overall assessment of models’ simulation ability. Then, the potential change of the interannual variability of spring Hadley circulation and its interannual connection with East Asian summer circulations and precipitation under the A1B scenario are projected by using the outputs of these five climate models. To facilitate quantitative estimation of their change, five indices are exploited in this study. The Northern Hemispheric Hadley circulation index (HCI) is defined as the maximum value of the zonal mean mass stream function occurring within the latitudinal zone of 0°~30°N, and the western Pacific subtropical high index (WPSHI) as the 850 hPa geopotential height anomalies averaged over the region （10°~30°N，110°~150°E）. The difference of zonal wind anomalies at 850 hPa between the region （10°~20°N，100°~150°E）and （25°~35°N，100°~150°E）and that at 200 hPa between the region （25°~35°N，80°~150°E）and （40°~50°N，80°~150°E）are used to define the East Asian summer monsoon index (EASMI) and the East Asian Jet index (EAJI), respectively. The East Asian rainfall index is represented by mean precipitation over the region （27°~32°N，110°~130°E）. The multi-model ensemble (MME) results show that the interannual variability of the Northern Hemispheric Hadley circulation in spring tends to decrease by 23% in the late 21st century (2070~2099) as compared to the late 20th century (1970~1979). Concurrent with the decreased interannual variability of spring Hadley circulation, its linkage to summer western Pacific subtropical high and East Asian summer monsoon is also projected to be weakened. The correlation coefficients between spring HCI and summer WPSHI (EASMI) decrease from 0.44 (－0.46) in the late 20th century to 0.19 (－0.15) in the late 21st century. Such a change can be simulated consistently by individual models. In addition, the MME results suggest that the association of spring Hadley circulation with summer East Asian jet and precipitation will be weakened as well, however, there are discrepancies in the change of their relationship among individual models.

In order to address the possible change of the Hadley circulation in response to global warming in the future, the ability of coupled climate models in simulating the temporal and spatial features of Hadley circulation is assessed by a comparison with the observation during 1970-1999. On this basis, three models which can well reproduce the spatial structure and the temporal change of the intensity and expansion of Hadley circulation are selected as the ensemble to project its possible change under the A1B scenario. The projection results show that the Northern Hemispheric Hadley circulation tends to weaken in four seasons but with weaker change in spring during the late 21st century（2070-2099） as compared to the period 1970-1979. The Southern Hemispheric Hadley circulation will also weaken in winter and summer, while its change in spring and autumn is not significant. In addition, except a southward shift in summer, the Hadley circulation in the Northern Hemisphere will exhibit a northward expansion in other three seasons during the late 21st century. The Hadley circulation in the Southern Hemisphere will move poleward in all seasons. Moreover, the upward shift of the Hadley circulation in the vertical may appear in both hemispheres in a warmer climate.

Changes in precipitation minus evaporation (P–E) are analyzed to investigate the possible impacts of climate change on water resource conditions in China. Simulations of SRES A1B and 20C3M scenarios from the WCRP CMIP3 GCMs are employed in the study. Time slice analysis shows that there would be more annual mean P–E across China in 2040–2055 and 2080–2099, compared to 1980–1999, with the largest percentage change over Northwest China and the Bohai Rim area. Precipitation and evaporation would also increase over entire China during these two periods. Annual mean P–E, precipitation, and evaporation averaged over the whole China and its eight sub-areas all yield generally upward trends during the 21st century. This indicates that on annual mean scale, the global warming related precipitation dominates the hydroclimate conditions in China. On seasonal mean scale, although precipitation is projected to increase over China, P–E exhibits both decreasing and increasing trends over certain regions of China. This suggests that the variation of global warming related evaporation dominates hydroclimate conditions over some parts of China, especially in northern China. Therefore, in hydroclimate condition projections, considering both evaporation and precipitation changes should be more reasonable than considering only precipitation.

http://www.cmsjournal.net/qxxb_en/ch/reader/view_abstract.aspx?file_no=20120309&flag=1

This study examines the skills in simulating interannual variability of northwestern Pacific (NWP) summer climate in twelve AMIP II atmospheric general circulation models (AGCMs). The models show a wide range of skills, among those HadGAM1 showed the highest fidelity and thus may be a better choice for studying East Asian–NWP summer climate. To understand the possible causes for the difference among the models, five models (HadGAM1, ECHAM5, AM2.1, MIROC-hi, CAM3), which have various skills ranging from the highest, medium to the minor, were selected for analyses. The simulated teleconnection of NWP summer climate with sea surface temperatures (SSTs) in the tropical Indian and Pacific oceans was first compared. HadGAM1 reproduces suppressed (intensified) rainfall during El Niño (La Niña) events and captures well the remote connection with the tropical Indian Ocean, while the other models either underestimate (ECHAM5, AM2.1, MIROC-hi) or fail to reproduce (CAM3) these teleconnections. The Walker Cell and diabatic heating were further compared to shed light on the underlying physical mechanisms for the difference. Consistent with the best performance in simulating interannual rainfall, HadGAM1 exhibits the highest skill in capturing the observed climatology of Walker Cell and diabatic heating. These results highlight the key roles of model’s background climatology in Walker Cell and diabatic heating, thus providing important clues to improving model’s ability.

The influence of local black carbon (BC) on

monthly mean precipitation and the associated circulation

in South Asia is investigated. The results show that the

amplified shortwave radiative heating rate by BC absorption

enhances convective activity near the Himalayas and the

southern Tibetan Plateau with increased rainfall anomalies

in April and May, which is consistent with previous studies.

However, the enhanced vertical motions and the precipitation

ultimately lead towards cooling of the lower troposphere

especially in May, which is extended till June. This

favored negative rainfall responses in June, implying delay

in the onset of South Asian summer monsoon rainfalls over

Arabian Sea and western parts of the subcontinent. The

negative precipitation response is further associated with

the prevailing anomalous high pressure and the anticyclonic

wind circulations induced by BC. Thus, we present here one

different feature associated with BC-induced elevated heat

pump-like circulations in South Asia.

This paper addresses the interdecadal variation of the West African summer monsoon (WASM) along with its background of atmospheric circulation and possible physical mechanism over the past 32 years (1979-2010). It is indicated that the WASM starts to strengthen from 1998 as the rainfall begins to increase over western West Africa on the whole, which shows a new interdecadal variation. In this interdecadal variation, the strengthened ascending motion corresponding to enhanced divergence (convergence) movement on the upper (lower) troposphere is prone to develop the local circulation of the monsoon. Moreover, the strengthened southwestern (eastern) wind on the lower (upper) level leads to more moisture from the Atlantic and the Gulf of Guinea transported to the West African continent. In addition, the summer subtropical high over the north Atlantic and western West Africa is strong and northward, and the tropical east wind is also strong. Statistically, the weaker (stronger) the spring North Atlantic Oscillation (NAO) is, the stronger (weaker) the tropical easterly is, and then the WASM is also stronger. But the effect of the NAO on the decadal variation of the WASM is not so significant from the north Atlantic anomaly sensitivity simulation with a single model. This is also an indication that the relationship between the WASM and NAO is complicated in an interdecadal time scale and is needed further study. In terms of sea surface temperature (SST) variation, the tendency is toward warming in the subtropical north Pacific, the south Pacific and north Atlantic. Numerical simulation experiments and data analysis show that the SST variation in the north Pacific plays an important role in the latest interdecadal strengthening of the WASM during the past 32 years, while the influences of the south Pacific and the north Atlantic SST anomalies are not so significant to the associated atmospheric circulation changes.

http://www.springerlink.com/content/m5k1874425q27760/

In this study, the effects of volcanic forcing on North Pacific climate variability, on interannual to decadal time scales, are examined using climate model simulations covering the last 600 years. The model used is the Bergen Climate Model, a fully coupled atmosphere–ocean general circulation model. It is found that natural external forcings, such as tropical strong volcanic eruptions (SVEs) and variations in total solar irradiance, play an important role in regulating North Pacific Decadal Variability (NPDV). In response to tropical SVEs the lower stratospheric pole–to–equator temperature gradient is enhanced. The North polar vortex is strengthened, which forces a significant positive Arctic Oscillation (AO). At the same time, dipole zonal wind anomalies associated with strong polar vortex propagate downward from the lower stratosphere. Through positive feedbacks in the troposphere, the surface westerly winds across the central North Pacific are significantly weakened, and positive sea level pressure anomalies are formed in the North Pacific. This anomalous surface circulation results in changes in the net heat fluxes and the oceanic advection across the North Pacific. As a result of this, warm water converges in the subtropical western North Pacific, where the surface waters in addition are heated by significantly reduced latent and sensible heat fluxes from the ocean. In the eastern and high–latitude North Pacific the ocean loses more heat, and large–scale decreases in sea surface temperatures are found. The overall response of this chain of events is that the North Pacific enters a negative phase of the Pacific decadal oscillation (PDO), and this negative phase of the PDO is maintained for several years. It is thus concluded that the volcanic forcing plays a key role in the phasing of the PDO. The model results furthermore highlight the important role of troposphere–stratosphere coupling, tropical–extratropical teleconnections and extratropical ocean–atmosphere interactions for describing NPDV.

While the Arctic region has been warming strongly in recent decades,anomalously large snowfall in recent winters has affected large parts of North America, Europe, and east Asia. Here we demonstrate that the decrease in autumn Arctic sea ice area is linked to changes in the winter Northern Hemisphere atmospheric circulation that have some resemblance to the negative phase of the winter Arctic oscillation. However, the atmospheric circulation change linked to the reduction of sea ice shows much broader meridional meanders in midlatitudes and clearly different interannual variability than the classical Arctic oscillation. This circulation change results in more frequent episodes of blocking patterns that lead to increased cold surges over large parts of northern continents. Moreover, the increase in atmospheric water vapor content in the Arctic region during late autumn and winter driven locally by the reduction of sea ice provides enhanced moisture sources, supporting increased heavy snowfall in Europe during early winter and the northeastern and midwestern United States during winter. We conclude that the recent decline of Arctic sea ice has played a critical role in recent cold and snowy winters.

In this paper, studies on extreme climate in China including extreme temperature and precipitation, dust

weather activity, tropical cyclone activity, intense snowfall and cold surge activity, floods, and droughts

are reviewed based on the peer-reviewed publications in recent decades. The review is focused first on

the climatological features, variability, and trends in the past half century and then on simulations and

projections based on global and regional climate models. As the annual mean surface air temperature (SAT) increased throughout China, heat wave intensity and frequency overall increased in the past half century, with a large rate after the 1980s. The daily or yearly minimum SAT increased more significantly than the mean or maximum SAT. The long-term change in precipitation is predominantly characterized by the so-called southern flood and northern drought pattern in eastern China and by the overall increase over Northwest China. The interdecadal variation of monsoon, represented by the monsoon weakening in the end of 1970s,

is largely responsible for this change in mean precipitation. Precipitation-related extreme events (e.g., heavy rainfall and intense snowfall) have become more frequent and intense generally over China in the recent years, with large spatial features. Dust weather activity, however, has become less frequent over northern China in the recent years, as result of weakened cold surge activity, reinforced precipitation, and improved vegetation

condition. State-of-the-art climate models are capable of reproducing some features of the mean climate and extreme climate events. However, discrepancies among models in simulating and projecting the mean and extreme climate are also demonstrated by many recent studies. Regional models with higher resolutions often perform better than global models. To predict and project climate variations and extremes, many new approaches and schemes based on dynamical models, statistical methods, or their combinations have been developed, resulting in improved skills. With the improvements of climate model capability and resolution as well as our understanding of regional climate variability and extremes, these new approaches and techniques are expected to further improve the prediction and projection on regional climate variability and extremes over China in the future.

In this study, the water vapor sources for the precipitation processes in southeastern China (SECN) during 1981–2010 were investigated using atmospheric reanalysis data. We also studied the factors influencing the summer atmospheric moisture over SECN. These two issues are all closely related to the climate signals recorded in stalagmites recovered from caves in SECN. Result supports that the atmospheric water vapor over SECN during the whole summer time is primarily transported from the Indian Ocean. However, the vertically integrated water vapor content throughout the year in SECN has two main sources: the Indian Ocean and the tropical western Pacific. In addition, the water vapor transport for the precipitation processes in SECN has complex vertical structure. At approximately 700 hPa to 500 hPa, part of the water vapor for the precipitation in SECN comes from the Arab-Caspian region. Finally, the water vapor content over SECN is regulated primarily by both the Indian and East Asian monsoons. Further analysis indicated that the variability of the East Asian summer monsoon is substantially regulated by the western Pacific subtropical high, the Eurasia–Atlantic thermal conditions, as well as the large-scale Eurasia-Atlantic atmospheric circulation. Therefore, the SECN Cave proxies can record the signals from faraway middle and high latitude Eurasia-Atlantic climate, besides the regional East Asian monsoon and remote Indian monsoon.

Using the experiments undertaken by 36 climate models participating in the Paleoclimate Modeling Intercomparison Project (PMIP), this study examines annual and seasonal surface temperatures over China during the mid-Holocene. Compared to the present or preindustrial climate, 35 out of the 36 PMIP models reproduced colder-than-baseline annual temperature, with an average cooling of 0.4 K, during that period. Seasonal temperature change followed closely the change in incoming solar radiation at the top of the atmosphere over China during the mid-Holocene. Temperature was reduced (elevated) in boreal winter and spring (summer) in all of the PMIP models, with an average of 1.4 K (1.0 K) at the national scale. Colder (warmer)-than-baseline temperatures were derived from 14 of the 16 atmosphere-only (18 of the 20 coupled) models during the mid-Holocene boreal autumn. Interactive ocean was found to lead to a warming effect on annual (0.3 K), boreal winter (0.5 K), and boreal autumn (0.7 K) temperatures, with reference to the atmosphere-only models. Interactive vegetation had little impact in terms of six pairs of coupled models with and without vegetation effects. The above results are in stark contrast to warmer-than-present annual and winter climate conditions as derived from multiproxy data for the mid-Holocene. Coupled models generally perform better than atmosphere-only models.

Considering the different uplifting time of different subregions of the Himalaya-Tibetan Plateau (TP), a series of numerical simulations have been conducted with the Community Atmosphere Model (CAM4) developed at the National Center for Atmospheric Research to explore the effects of the phased tectonic uplift of the Himalaya-TP on the evolution of Asian summer monsoons. The results show that the uplifts of the Himalaya and northern TP significantly affect the evolutions of South Asian summer monsoon and northern East Asian summer monsoon respectively. That is, the tectonic uplift of the Himalaya intensifies the South Asian summer monsoon circulation and increases the precipitation in South Asia, whereas the uplift of the northern TP intensifies the northern East Asian summer monsoon circulation and increases the precipitation in northern East Asia. Compared with previous simulations, current comparative analyses of modeling results for different subregional uplifts within the Himalaya-TP help deepen our understanding of the evolutionary history of Asian monsoons.

本研究针对我国内陆新疆地区在20世纪80年代末出现由暖干向暖湿的年代际转型,从大气环流因子进行归因分析.结果显示,位于东亚沿海地区的东亚-太平洋 型遥相关波列(EAP)的强度和位置的年代际加强和偏移对于新疆地区此次气候的干湿转型具有重要贡献.转型之前EAP强度偏弱,位置相对偏东,对新疆夏季 降水变化没有明显贡献,且影响新疆夏季降水发生的主要环流系统是位于中纬度欧亚大陆上空的异常纬向波列.转型后EAP强度偏强,位置相对前期向西偏移,因 此从西北太平洋向我国内陆地区的异常水汽输送显著增强,使得新疆地区大气含水量增加,从而导致20世纪80年代末以后新疆夏季降水的增加.

A new statistical downscaling (SD) scheme is proposed to predict summertime multisite rainfall measurements

in China. The potential predictors are multiple large-scale variables from operational dynamical

model output.Akey step in this SD scheme is finding optimal predictors that have the closest and most stable

relationship with rainfall at a given station. By doing so, the most robust signals from the large-scale circulation

can be statistically projected onto local rainfall, which can significantly improve forecast skill in predicting

the summer rainfall at the stations. This downscaling prediction is performed separately for each

simulation with a leave-one-out cross-validation approach and an independent sample validation framework.

The prediction skill scores exhibited at temporal correlation, anomaly correlation coefficient, and root-meansquare

error consistently demonstrate that dynamical model prediction skill is significantly improved under

the SD scheme, especially in the multimodel ensemble strategy. Therefore, this SD scheme has the potential

to improve the operational skill when forecasting rainfall based on the coupled models.

Based on hindcasts obtained from the ‘‘Development

of a European Multimodel Ensemble system for

seasonal to inTERannual prediction’’ (DEMETER) project, this study proposes a statistical downscaling (SD) scheme suitable for global precipitation forecasting. The key idea of this SD scheme is to select the optimal predictors that

are best forecast by coupled general circulation models (CGCMs) and that have the most stable relationships with observed precipitation. Developing the prediction model and further making predictions using these predictors can extract useful information from the CGCMs. Cross-validation

and independent sample tests indicate that this SD

scheme can significantly improve the prediction capability of CGCMs during the boreal summer (June–August), even over polar regions. The predicted and observed precipitations are significantly correlated, and the root-meansquare-error of the SD scheme-predicted precipitation is largely decreased compared with the raw CGCM predictions. An inter-model comparison shows that the multimodel

ensemble provides the best prediction performance.

This study suggests that combining a multi-model ensemble with the SD scheme can improve the prediction skill for precipitation globally, which is valuable for current operational precipitation prediction.

Based on daily precipitation data, the spatial-temporal features of heavy rainfall events (HREs) during

1960–2009 are investigated. The results indicate that the HREs experienced strong decadal variability in

the past 50 years, and the decadal features varied across regions. More HRE days are observed in the 1960s,

1980s, and 1990s over Northeast China (NEC); in the 1960s, 1970s, and 1990s over North China (NC); in

the early 1960s, 1980s, and 2000s over the Huaihe River basin (HR); in the 1970s–1990s over the mid-lower

reaches of the Yangtze River valley (YR); and in the 1970s and 1990s over South China (SC). These decadal

changes of HRE days in eastern China are closely associated with the decadal variations of water content and

stratification stability of the local atmosphere. The intensity of HREs in each sub-region is also characterized

by strong decadal variability. The HRE intensity and frequency co-vary on the long-term trend, and show

consistent variability over NEC, NC, and YR, but inconsistent variability over SC and HR. Further analysis

of the relationships between the annual rainfall and HRE frequency as well as intensity indicates that the

HRE frequency is the major contributor to the total rainfall variability in eastern China, while the HRE

intensity shows only relative weak contribution.

The authors investigate monsoon change in East Asia in the 21st century under the Special Report on Emissions Scenarios (SRES) A1B scenario using the results of a regional climate model, RegCM3, with a high horizontal resolution. First, the authors evaluate the model's performance compared with NCEP-NCAR reanalysis data, showing that the model can reliably reproduce the basic climatology of both winter and summer monsoons over East Asia. Next, it is found that the winter monsoon in East Asia would slightly weaken in the 21st century with spatial differences. Over northern East China, anomalous southerly winds would dominate in the mid- and late-21st century because the zonal land-sea thermal contrast is expected to become smaller, due to a stronger warming trend over land than over ocean. However, the intensity of the summer monsoon in East Asia shows a statistically significant upward trend over this century because the zonal land-sea thermal contrast between East Asia and the western North Pacific would become larger, which, in turn, would lead to larger sea level pressure gradients throughout East Asia and extending to the adjacent ocean.

Here we propose a new concept, the Pan-Asian monsoon, and use empirical orthogonal function (EOF) analysis and linear re-gression approach to define it and to analyze the monsoon-related rainfall variability. The Pan-Asian monsoon is referred to as the monsoon occurred over the great region (60°E–140°E,10°S–35°N), consisting of the Indian monsoon, Southeast Asian monsoon, East Asian monsoon, and Western North Pacific monsoon. The Pan-Asian monsoon region is the principal region of the summer rainfall over the Asian-Pacific monsoon region and is also water vapor channel connecting several Asian-Pacific sub-monsoon systems. The first EOF mode of the Pan-Asian monsoon precipitation (PAMP_F) shows a meridional tripole pattern with more (less) rainfall zonal belt over the Bay of Bengal (BOB), the Indo-China Peninsula, South China, the South China Sea (SCS), Philippines and the Philippine Sea, and less (more) rainfall on both sides. The first rainfall mode is associ-ated with the weakened Somali cross-equatorial flows, enhanced southerly over the eastern coast of Australia, and strength-ened westerly over the tropical Pacific. The first EOF rainfall mode shows a close relationship with the simultaneous El Niño- Southern Oscillation (ENSO) and Pacific South America (PSA). The preceding spring and simultaneous summer Antarctic Oscillation (AAO) in the western Hemisphere (AAO in Pacific) has a connection with the first summer rainfall mode of the Pan-Asian monsoon. Because the main influence factors are over the Pacific, the first rainfall mode is named as the Pacific mode. The second mode of the Pan-Asian monsoon precipitation (PAMP_S) shows a dipole pattern from northeast to south-west, which is associated with the weakened Somali cross-equatorial flows, enhanced easterlies over the Maritime Continent, and weak easterly over the tropical Pacific. The second rainfall model has a close relationship with the atmospheric convection activity and the sea surface temperature variability over the Maritime Continent and South Indian Ocean. Because the influ-ence factors are mainly over the eastern Hemisphere, the second rainfall mode of the Pan-Asian monsoon is named as the In-dian Ocean mode.

Mineral dust aerosol can be transported over the nearby oceans and influence the energy balance at the sea surface. The role of dust-induced sea surface temperature (SST) responses in simulations of the climatic effect of dust is examined by using a general circulation model with online simulation of mineral dust and a coupled mixed-layer ocean model. Both the longwave and shortwave radiative effects of mineral dust aerosol are considered in climate simulations. The SST responses are found to be very influential on simulated dust-induced climate change, especially when climate simulations consider the two-way dust-climate coupling to account for the feedbacks. With prescribed SSTs and dust concentrations, we obtain an increase of 0.02 K in the global and annual mean surface air temperature (SAT) in response to dust radiative effects. In contrast, when SSTs are allowed to respond to radiative forcing of dust in the presence of the dust cycle-climate interactions, we obtain a global and annual mean cooling of 0.09 K in SAT by dust. The extra cooling simulated with the SST responses can be attributed to the following two factors: (1) The negative net radiative forcing of dust at the surface reduces SST, which decreases latent heat fluxes and upward transport of water vapor, resulting in less warming in the atmosphere; (2) The positive feedback between SST responses and dust cycle. The dust-induced reductions in SST lead to reductions in precipitation (or wet deposition of dust) and hence increase the global burden of small dust particles. These small particles have strong scattering effects, which enhance the dust cooling at the surface and further reduce SSTs.

The climatic responses to the direct radiative effect of dust aerosol at the Last Glacial Maximum (LGM) are examined using a general circulation model with online simulation of dust. The predicted global dust emission at the LGM is 2.3 times as large as the present-day value, which is the combined effect of the expansion of dust sources and the favorable meteorological parameters (MPs, such as the strong surface wind and the low air humidity) under the LGM climate. Simulated global dust emission is 1966 Tg yr-1 with present-day dust sources and MPs, 2820 Tg yr-1 with LGM dust sources and current MPs, 2599 Tg yr-1 with present-day dust sources and LGM MPs, and 4579 Tg yr-1 with LGM sources and MPs. The simulated percentage increases of dust concentrations are the largest at high latitudes in both hemispheres, which are consistent with the deposition data from geological records. The LGM dust is estimated to exert global annual mean shortwave (SW) and longwave (LW) radiative forcings (RF) of, respectively, -4.69 W m-2 and +1.70 W m-2 at the surface, and -0.58 W m-2 and + 0.68 W m-2 at the top of the atmosphere. On a global and annual mean basis, surface air temperature (SAT) is predicted to be reduced by 0.18 K and precipitation is reduced by 0.06 mm day-1, as a result of the net (SW and LW) radiative effect of dust at the LGM. Two sensitivity studies are performed to identify the uncertainties in simulated climatic effect of LGM dust that arise from the assumed LW and/or SW absorption by dust: (1) in the absence of dust LW radiative effect, the LGM global and annual mean SAT is predicted to be further reduced by 0.19 K; and (2) when the single scattering albedo of the Saharan dust at 0.55 μm is increased from 0.89 to 0.98 in the LGM climate simulation, the LGM dust-induced annual and global mean surface cooling increases from 0.18 K to 0.63 K even with both SW and LW radiative effects of dust. In these two sensitivity studies, the LGM dust is predicted to induce an average cooling of, respectively, 0.42 and 0.72 K in SAT over the tropical oceans.

snowfall occurred in NEC, with 26.8 mm of accumulated

water-equivalent snow over Harbin, the capital of the most

eastern province in NEC. In this study, the major features

of the snowfall and associated large-scale circulation and

the predictability of the snowfall are analyzed using both

observations and models. The Siberia High intensified and

shifted southeastward from 10 days before the snowfall,

resulting in intensifying the low-pressure system over NEC

and strengthening the East Asian Trough during 12–13

April. Therefore, large convergence of water vapor and

strong rising motion appeared over eastern NEC, resulting

in heavy snowfall. Hindcast experiments were carried out

using the NCAR Weather Research and Forecasting (WRF)

model in a two-way nesting approach, forced by NCEP

Global Forecast System data sets. Many observed features

including the large-scale and regional circulation anomalies

and snowfall amount can be reproduced reasonably

well, suggesting the feasibility of the WRF model in

forecasting extreme weather events over NEC. A quantitative

analysis also shows that the nested NEC domain

simulation is even better than mother domain simulation in

simulating the snowfall amount and spatial distribution,

and that both simulations are more skillful than the NCEP

Global Forecast System output. The forecast result from

the nested forecast system is very promising for an operational

purpose.

By using the Betts-Miller-Janjic, Grell-Devenyi, and Kain-Fritsch cumulus convective parameterization

schemes in theWeather Research and Forecasting (WRF) model, long time simulations from 2000 to 2009 are

conducted to investigate the impacts of different cumulus convective parameterization schemes on summer

monsoon precipitation simulation over China. The results show that all the schemes have the capability

to reasonably reproduce the spatial and temporal distributions of summer monsoon precipitation and the

corresponding background circulation. The observed north-south shift of monsoon rain belt is also well

simulated by the three schemes. Detailed comparison indicates that the Grell-Devenyi scheme gives a better

performance than the others. Deficiency in simulated water vapor transport is one possible reason for the

precipitation simulation bias.

A statistical downscaling approach based on multiple-linear-regression (MLR) for the prediction of summer precipitation anomaly in southeastern China was established, which was based on the outputs of seven operational dynamical models of Development of a European Multi-model Ensemble System for Seasonal to Interannual Prediction (DEMETER) and observed data. It was found that the anomaly correlation coefficients (ACCs) spatial pattern of June-July-August (JJA) precipitation over southeastern China between the seven models and the observation were increased significantly; especially in the central and the northeastern areas, the ACCs were all larger than 0.42 (above 95% level) and 0.53 (above 99% level). Meanwhile, the root-mean-square errors (RMSE) were reduced in each model along with the multi-model ensemble (MME) for some of the stations in the northeastern area; additionally, the value of RMSE difference between before and after downscaling at some stations were larger than 1 mm d1. Regionally averaged JJA rainfall anomaly temporal series of the downscaling scheme can capture the main characteristics of observation, while the correlation coefficients (CCs) between the temporal variations of the observation and downscaling results varied from 0.52 to 0.69 with corresponding variations from 0.27 to 0.22 for CCs between the observation and outputs of the models.

The relationship between winter sea surface temperature (SST) east of Australia and summer precipitation in the Yangtze River valley and a possibly related physical mechanism were investigated using observation data. It is found that winter SST east of Australia is correlated positively to summer precipitation in the Yangtze River valley. When the SST east of Australia becomes warmer in winter, the western Pacific subtropical high and the East Asian westerly jet tend to shift southward the following summer, concurrent with low-level southwesterly anomalies over eastern China. These conditions favor precipitation increase in the Yangtze River valley, whereas the opposite conditions favor precipitation decrease. The influence of winter SST east of Australia on East Asian summer atmospheric circulations may occur in two ways. First, by an anomalous SST signal east of Australia in winter that persists through the following summer, thus affecting East Asian atmospheric circulations via the inter-hemispheric teleconnection. Second, when the SST east of Australia is warmer in winter, higher SST appears simultaneously in the southwest Indian Ocean and subsequently develops eastward by local air–sea interaction. As a result, the SST in the Maritime Continent increases in summer, which may lead to an anomalous change in East Asian summer atmospheric circulations through its impact on convection.

A statistical dynamic model for forecasting Chinese landfall of tropical cyclones (CLTCs) was developed

based on the empirical relationship between the observed CLTC variability and the hindcast atmospheric

circulations from the Pusan National University coupled general circulation model (PNU-CGCM). In the

last 31 years, CLTCs have shown strong year-to-year variability, with a maximum frequency in 1994 and a

minimum frequency in 1987. Such features were well forecasted by the model. A cross-validation test showed

that the correlation between the observed index and the forecasted CLTC index was high, with a coefficient

of 0.71. The relative error percentage (16.3%) and root-mean-square error (1.07) were low. Therefore the

coupled model performs well in terms of forecasting CLTCs; the model has potential for dynamic forecasting

of landfall of tropical cyclones.

This paper describes a dynamical downscaling

simulation over China using the nested model system,

which consists of the modified Weather Research and

Forecasting Model (WRF) nested with the NCAR Community

Atmosphere Model (CAM). Results show that

dynamical downscaling is of great value in improving the

model simulation of regional climatic characteristics.

WRF simulates regional detailed temperature features

better than CAM. With the spatial correlation coefficient

between the observation and the simulation increasing

from 0.54 for CAM to 0.79 for WRF, the improvement in

precipitation simulation is more perceptible with WRF.

Furthermore, the WRF simulation corrects the spatial bias

of the precipitation in the CAM simulation.

Hail is one of the important weather disasters

that affects the Beijing-Tianjin (BT) region. To better understand and to improve the forecasting of hail events over the BT region, the precursor weather conditions for hail based on 30 previous hail events were derived. It was found that the high-level trough and low-level cold front over the Mongolian region, the accumulated convective available potential energy, the decrease of the height of

the 0C-isotherm in the morning, and the persistence and intensification of these factors from morning to afternoon are valuable clues for forecasting the occurrence of hail events over the BT region.

This study evaluates the ability of the global coupled climate models in hindcasting the Arctic Oscillation

(AO) and Antarctic Oscillation (AAO). The results show that the models can well simulate the spatial

distribution of AO with better results in winter than in spring. In the troposphere in spring, the simulation

of AO on the whole is still relatively good with a comparatively high correlation with the NCEP/NCAR

reanalysis. The models can also well reproduce the spatial distribution of AAO throughout the year at all

levels of the troposphere, and the spatial simulation is better at 850 hPa than at the surface. Although

the simulation is better in winter than in other seasons, the seasonal variation is not so significant and the differences among different models are relatively small. In addition, the capability of the models for “predicting” the AO and the AAO index time series is limited, because only a few models can capture their observed interannual variability at the 95% significance level.

This study evaluates the ability of the Abdus Salam International Center for Theoretical Physics (ICTP) version 3 Regional Climate Model (RegCM3) in simulating the summer rainfall amount and distribution and large-scale circulation over the Huaihe River basin of China. We conducted the simulation for the period of 1982-2001 and the wet year of 2003 to test the ensemble simulation capacity of RegCM3. First, by comparing the simulated rainfall amount and distribution against the observations, it is found that RegCM3 can reproduce the rainfall pattern and its annual variations. In addition, the simulated spatial patterns of 850-hPa wind and specific humidity fields are close to the observations, although the wind speed and humidity values are larger. Finally, the ensemble simulation of RegCM3 for summer 2003 failed to capture the spatial distribution and underestimated the magnitude of the precipitation anomalies, and the reasons are analyzed.

It has been well documented that vegetation plays an important role in the climate system. However, vegetation is typically kept constant when climate models are used to project anthropogenic climate change under a range of emission scenarios in the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emission Scenarios. Here, an atmospheric general circulation model, and an asynchronously coupled system of an atmospheric and an equilibrium terrestrial biosphere model are forced by monthly sea surface temperature and sea ice extent for the periods 2051--2060 and 2090--2098 as projected with 17 atmosphere--ocean general circulation models participating in the IPCC Fourth Assessment Report, and by appropriate atmospheric carbon dioxide concentrations under the A2 emission scenario. The effects of vegetation feedback under future global warming are then investigated. It is found that the simulated composition and distribution of vegetation during 2051--2060 (2090--2098) differ greatly from the present, and global vegetation tends to become denser as expressed by a 21% (36%) increase in global mean leaf area index, which is most pronounced at the middle and high northern latitudes. Vegetation feedback has little effect on globally averaged surface temperature. On a regional scale, however, it induces statistically significant changes in surface temperature, in particular over most parts of continental Eurasia east of about 60degE where annual surface temperature is expected to increase by 0.1--1.0 K, with an average of about 0.4 K for each future period. These changes can mostly be explained by changes in surface albedo resulting from vegetation changes in the context of future global warming.

The most severe snowstorm and freezing-rain event in the past 50 years hit central and southern China in January 2008. One of the main reasons for the anomalous climate event was the occurrence of atmospheric circulation anomalies over middle and high latitudes, particularly the persistent blocking that occurred over the Ural Mountains. Along with atmospheric anomalies, a strong La Ni~na event in the Paci¯c and warm sea surface temperature anomalies (SSTAs) in the North Atlantic were the most signi¯cant in the lower boundary. Since a brief analysis suggests that La Ni~na exerts no signi¯cant impact on the Urals, the key

point of focus in this study is on the role of the warmer SSTAs in the North Atlantic. Based on an observational composite, North Atlantic SSTAs pattern when the height anomaly over the Urals is strongly positive is found similar to that in January 2008, but no signi¯cant SSTAs occurred

elsewhere, such as the Paci¯c. Using an atmospheric general circulation model, ECHAM5, the impact of

North Atlantic SSTAs on the extratropical atmosphere circulation in the event was investigated. The results show that the warm SSTAs strengthened the blocking high over the Urals, through anomalous transient eddies. The consistency between the study model and the observational composite indicates that the warm SSTAs in the North Atlantic were indeed an important factor in the formation of the snowstorm disaster of January 2008.

A pre‐industrial multicentury simulation with Bergen Climate Model Version 2

(BCM in brief) is used to investigate the linkage between the Atlantic Multidecadal

Oscillation (AMO) and the Indian Summer Monsoon (ISM). The results suggest that the

model reproduces the general characters of the observed linkage between AMO and ISM,

and that a positive AMO favors more rainfall over India from July to October. The

ISM is intensified and the seasonal withdrawal of ISM delayed with one month, in

agreement with previous observational and model’s results. Further diagnoses indicate that

this impact is achieved through an atmospheric teleconnection pattern. A propagating

Rossby wave train from the North Atlantic across South Asia leads to enhanced South

Asia high and consequently a strengthening of the ISM.

The impact of the tropical oceanic forcing on the East Asian winter-to-early spring climate is investigated by implementing the pacemaker technique in the slab mixed-layer version of the Geophysical Fluid Dynamics Laboratory AM2.1 atmospheric general circulation model. The results demonstrate that oceanic forcing from the deep tropical eastern Pacific (DTEP) can instigate the Pacific-East Asia teleconnection and that the Philippine Sea anticyclone and the associated air-sea interaction are crucial for the realization of the impact of the teleconnection over East Asia. Comparison among cases in which the pace-maker is designated over the DTEP region, DTEP plus the Indian Ocean, and the whole tropical oceans indicates that tropical oceanic forcing outside of the Niño regions can also exert significant influence on East Asian climate. As a result, a total of 30% of the variance of the East Asian precipitation index can be accounted for by the tropical oceanic forcing.

A new seasonal prediction model for annual tropical storm numbers (ATSNs) over the western North Pacific was developed using the preceding January-February (JF) and April-May (AM) grid-point data at a resolution of 2.5°×2:5°. The JF and AM mean precipitation and the AM mean 500-hPa geopotential height in the Northern Hemisphere, together with the JF mean 500-hPa geopotential height in the Southern Hemisphere, were employed to compose the ATSN forecast model via the stepwise multiple linear regression technique. All JF and AM mean data were confined to the Eastern Hemisphere. We established two empirical prediction models for ATSN using the ERA40 reanalysis and NCEP reanalysis datasets, respectively, together with the observed precipitation. The performance of the models was verified by cross-validation. Anomaly correlation coefficients (ACC) at 0.78 and 0.74 were obtained via comparison of the retrospective predictions of the two models and the observed ATSNs from 1979 to 2002. The multiyear mean absolute prediction errors were 3.0 and 3.2 for the two models respectively, or roughly 10% of the average ATSN. In practice, the final prediction was made by averaging the ATSN predictions of the two models. This resulted in a higher score, with ACC being further increased to 0.88, and the mean absolute error reduced to 1.92, or 6.13% of the average ATSN.

The Middle Pliocene (ca 3.12–2.97 Ma) is a recent warm period in the Earth’s history. In many respects, the warmth of the Middle Pliocene is similar to the probable warm situation of the late 21st century predicted by climate models. Understanding the

Middle Pliocene climate is important in predicting the future climate with global warming. Here, we used the latest reconstructions

for the Middle Pliocene—Pliocene Research Interpretation and Synoptic Mapping (PRISM) version 3—to simulate the Middle

Pliocene climate with a fully coupled model Fast Ocean Atmosphere Model. From comparison of the results of simulations

with reconstructions, we considered two important scientific topics of Middle Pliocene climate modeling: extreme warming in the

subpolar North Atlantic and a permanent El Niño in the tropical Pacific. Our simulations illustrate that the global annual mean sea

surface temperature (SST) in the Middle Pliocene was about 2.3°C higher than that in the pre-industrial era. The warming was

stronger at mid- and high latitudes than at low latitudes. The simulated SST changes agree with SST reconstructions in PRISM3

data, especially for the North Atlantic, North Pacific and west coast of South America. However, there were still discrepancies

between the simulation of the SST and reconstructions for the subpolar North Atlantic and tropical Pacific. In the case of the Atlantic,

the weakened meridional overturning circulation in the simulation did not support the reconstruction of the extremely warm

condition in the subpolar North Atlantic. In the case of the tropical Pacific, the whole ocean warmed, especially the eastern tropical

Pacific, which did not support the permanent El Niño suggested by the reconstruction. From evaluation of the modeling and

reconstruction, we suggest that the above discrepancies were due to uncertainties in reconstructions, difficulties in paleoclimate

modeling and deficiencies of climate models. The discrepancies should be reduced through consideration of both the modeling

and data.

Using observational daily maximum temperature of Chinese 181 stations for the period of 1957~2004, the spatio-temporal features of the climatology and decadal variability of the extreme hot event (EHE) frequency, intensity, onset date (EHE-OD), and termination date (EHE_TD) are investigated. The climatological analysis indicates that southeastern China and Xinjiang are the two major domains for the EHE, and eastern China is a region with a strong interannual variability. The EHE experienced strong decadal variability in the last 48 years. The variabilities of the frequency and intensity are consistent, and the variabilities of the EHE_OD and EHE_TD are similar. Based on the EHE spatio-temporal feature, the whole China can be divided into four sub-regions: Southern China, central China, eastern northern China, and Northwest China. The EHE frequency is high in the 1960s and the 1980s for southern China,in the 1960s and the 1990s for central China, and in the 1990s for northern China. Further, the atmospheric circulations which are responsible for the interannual and decadal variability of the EHE in the above four sub-regions are explored. It suggests that the circulations impacting on the interannual and decadal variability are consistent. For northern China, the major circulation is the overlying geopotential height anomaly at middle-to-upper levels. For southern and central China, the major circulations are the overlying geopotential height anomaly at middle-to-upper levels and temperature advection by the meridional wind at lower levels.

Mineral dust aerosol can be transported over the nearby oceans and influence the energy balance at the sea surface. The role of dust-induced sea surface temperature (SST) responses in simulations of the climatic effect of dust is examined by using a general circulation model with online simulation of mineral dust and a coupled mixed-layer ocean model. Both the longwave and shortwave radiative effects of mineral dust aerosol are considered in climate simulations. The SST responses are found to be very influential on simulated dust-induced climate change, especially when climate simulations consider the two-way dust-climate coupling to account for the feedbacks. With prescribed SSTs and dust concentrations, we obtain an increase of 0.02 K in the global and annual mean surface air temperature (SAT) in response to dust radiative effects. In contrast, when SSTs are allowed to respond to radiative forcing of dust in the presence of the dust cycle-climate interactions, we obtain a global and annual mean cooling of 0.09 K in SAT by dust. The extra cooling simulated with the SST responses can be attributed to the following two factors: (1) The negative net radiative forcing of dust at the surface reduces SST, which decreases latent heat fluxes and upward transport of water vapor, resulting in less warming in the atmosphere; (2) The positive feedback between SST responses and dust cycle. The dust-induced reductions in SST lead to reductions in precipitation (or wet deposition of dust) and hence increase the global burden of small dust particles. These small particles have strong scattering effects, which enhance the dust cooling at the surface and further reduce SSTs.

The climatic responses to the direct radiative effect of dust aerosol at the Last Glacial Maximum (LGM) are examined using a general circulation model with online simulation of dust. The predicted global dust emission at the LGM is 2.3 times as large as the present-day value, which is the combined effect of the expansion of dust sources and the favorable meteorological parameters (MPs, such as the strong surface wind and the low air humidity) under the LGM climate. Simulated global dust emission is 1966 Tg yr-1 with present-day dust sources and MPs, 2820 Tg yr-1 with LGM dust sources and current MPs, 2599 Tg yr-1 with present-day dust sources and LGM MPs, and 4579 Tg yr-1 with LGM sources and MPs. The simulated percentage increases of dust concentrations are the largest at high latitudes in both hemispheres, which are consistent with the deposition data from geological records. The LGM dust is estimated to exert global annual mean shortwave (SW) and longwave (LW) radiative forcings (RF) of, respectively, -4.69 W m-2 and +1.70 W m-2 at the surface, and -0.58 W m-2 and + 0.68 W m-2 at the top of the atmosphere. On a global and annual mean basis, surface air temperature (SAT) is predicted to be reduced by 0.18 K and precipitation is reduced by 0.06 mm day-1, as a result of the net (SW and LW) radiative effect of dust at the LGM. Two sensitivity studies are performed to identify the uncertainties in simulated climatic effect of LGM dust that arise from the assumed LW and/or SW absorption by dust: (1) in the absence of dust LW radiative effect, the LGM global and annual mean SAT is predicted to be further reduced by 0.19 K; and (2) when the single scattering albedo of the Saharan dust at 0.55 μm is increased from 0.89 to 0.98 in the LGM climate simulation, the LGM dust-induced annual and global mean surface cooling increases from 0.18 K to 0.63 K even with both SW and LW radiative effects of dust. In these two sensitivity studies, the LGM dust is predicted to induce an average cooling of, respectively, 0.42 and 0.72 K in SAT over the tropical oceans.

The quality of simulated soil hydrological variables (i.e., soil moisture,evapotranspiration, and runoff) is largely dependent on the accuracy of meteorological forcing data, especially recipitation and air temperature. This issue is quantitatively

addressed here by running the Community Land Model CLM3.5) over China from 1993 to 2002 using the reanalysis‐based precipitation and air temperature and in situ observations in the meteorological forcing data set. Compared to the in situ measured soil moisture data, the CLM3.5 simulation can generally capture the spatial and seasonal ariations of soil moisture but produces too‐wet soil in northeastern and eastern China and too‐dry soil in northwestern China. This deficiency is significantly reduced when the in situ measured precipitation data are used to drive the model. An index is also

constructed to quantify the sensitivities of soil hydrological variables to variations of

precipitation and air temperature. The highest sensitivity of surface hydrological variables

to precipitation appears over semiarid regions, while the sensitivity to air temperature

for different variables varies regionally (semiarid regions for runoff and soil moisture and humid regions for evapotranspiration (ET)). Over semiarid regions, precipitation and air temperature are equally important to the simulations of soil hydrological variables. Over humid regions, in contrast, ET is more dependent on air temperature than on precipitation, while soil moisture and runoff are less affected by air temperature.

Four physically based land surface hydrology models driven by a common observation-based three-hourly meteorological data set were used to simulate soil moisture over China for the period 1950-2006. Monthly values of total column soil moisture from the simulations were converted to percentiles and an ensemble method was applied to combine all models simulations into a multimodel ensemble from which agricultural drought severities and durations were estimated. A cluster analysis method and severity-area-duration (SAD) algorithm were applied to the soil moisture data to characterize drought spatial and temporal variability. For drought areas greater than 150,000 km2 and durations longer than three months, a total of 76 droughts were identified during the 1950-2006 period. The duration of 50 of these droughts was less than 6 months. The five most prominent droughts, in terms of spatial extent and then duration, were identified. Of these, the drought of 1997-2003 was the most severe, accounting for the majority of the severity-area-duration envelope of events with areas smaller than 5 million km2. The 1997-2003 drought was also pervasive in terms of both severity and spatial extent. We also found that soil moisture in north central and northeastern China had significant downtrends, whereas most of Xinjiang, the Tibetan Plateau, and small areas of Yunnan province had significant uptrends. Regions with downtrends were larger than those with uptrends (37% versus 26 % of the land area), implying that over the period of analysis, the country has become slightly drier in terms of soil moisture. Trends in drought severity, duration, and frequency suggest that soil moisture droughts have become more severe, prolonged, and frequent during the past 57 years, especially for northeastern and central China, suggesting an increasing susceptibility to agricultural drought.

Using the results of 25 climate models under the framework of the Paleoclimate Modelling Intercomparison Project (PMIP) and available proxy data, this study examines the regional climate of China during the Last Glacial Maximum (LGM: 21,000 years ago). Compared to the baseline climate, results show that annual surface temperature decreased by 2.00°–7.00 °C in China during that period, with an average of 4.46 °C, for the ensemble mean of all models. Annual precipitation and evaporation during the LGM were 5–40% less than the baseline values, with an average reduction of 20% (0.60 mm/day) and a reduction of 21% (0.41 mm/day) at the national scale, based on results from15 out of the 25models. These models were selected for their ability to simulate the modern precipitation climatology and for the availability of suitable evaporation data. Both the geographical distribution and magnitude of changes in surface temperature, precipitation, and evaporation during the LGM varied with the seasons and with the models, particularly at the sub-regional scale. Model-data comparisons revealed that the 25models successfully reproduced the surface cooling trend during the LGM, but they failed to reproduce its magnitude in all four regions of comparison, particularly in the Hexi Corridor and in North and Northeast China. The simulations with computed sea surface temperatures (SSTs) were in better agreement with proxy estimates of surface temperature than those with prescribed SSTs. On the other hand, large-scale LGM-minus-baseline anomalies in annual precipitation minus evaporation agreed well, in a qualitative manner, with lake status-based reconstructions of changes in annual water budgets in East China and the region of 35°–42°N, 74°–97°E. On the eastern Qinghai–Tibetan Plateau, drier climates from the 15 models agreed with pollen-based reconstructions. For most parts of West China excluding the Qinghai–Tibetan Plateau, the simulations with computed (prescribed) SSTs are consistent (inconsistent) with reconstructed moister conditions.

Using the year-to-year increment approach, this study investigated the relationship of selected climatic elements with the increment time series of the summer rainfall between successive years in Northeast China, including the soil moisture content, sea surface temperature, 500 hPa geopotential height, and sea level pressure in the preceding spring for the period 1981–2008. Two spring predictors were used to construct the seasonal prediction model: the area mean soil moisture content in Northwest Eurasia and the 500 hPa geopotential height over Northeast China. Both the cross-validation and comparison with previous studies showed that the above two predictors have good predicting ability for the summer rainfall in Northeast China.

We examine equilibrium climate responses to the shortwave and/or longwave direct radiative effect of mineral dust aerosol using the Global transport Model of Dust (GMOD) embedded within a general circulation model (GCM). The presence of mineral dust aerosol in the atmosphere is estimated to exert global mean shortwave and longwave radiative forcings (RF) of -0.25 W m-2 and +0.27 W m-2, respectively, at the top of the atmosphere (TOA) and -1.95 W m-2 and +0.61 W m-2 at the surface. Climatic effect of dust is simulated using two different approaches. In the first approach, monthly mean fields of dust simulated a priori are used in the radiative transfer module of the GCM to drive climate change, with levels of dust fixed during the climate integration (denoted as simulation FIXDST). In the second approach, dust aerosol interacts online with meteorology through the dust cycle and its direct radiative effect (denoted as simulation CPLD). With both longwave and shortwave RF of dust, predicted changes in global and annual mean surface air temperature and air temperature at 200 hPa are zero and +0.12 K, respectively, in FIXDST, and -0.06 K and +0.05 K in the CPLD simulation. The stronger cooling in CPLD than in FIXDST is a result of a 13% higher dust burden in CPLD with dust-climate interactions. Although dust longwave radiative effect is predicted to offset a large portion of its shortwave effect on a global and annual mean basis, dust shortwave effect dominates during the daytime, and the longwave effect prevails at night, which is found to be very important for predictions of temperature. For example, over the Sahara Desert, the changes in annual mean, annual mean daytime, and annual mean nighttime surface air temperature are predicted to be +0.32 K, -0.11 K, and +0.68 K, respectively, in the FIXDST simulation. The longwave and shortwave radiative effects of dust are predicted to have different impacts on the dust cycle in CPLD simulation; the solar radiative effect reduces dust emissions by increasing surface humidity and by reducing surface wind speed, while the thermal effect increases dust uplift through opposite changes in the meteorological parameters.

Direct climate responses to dust shortwave and longwave radiative forcing (RF) are studied using the NCAR Community Atmosphere Model Version 3 (CAM3). The simulated RF at the top of the atmosphere (TOA) is -0.45 W m-2 in the solar spectrum and +0.09 W m-2 in the thermal spectrum on a global average. The magnitude of surface RF is larger than the TOA forcing, with global mean shortwave forcing of -1.76 W m-2 and longwave forcing of +0.31 W m-2. As a result, dust aerosol causes the absorption of 1.1 W m-2 in the atmosphere. The RF of dust aerosol is predicted to lead to a surface cooling of 0.5 K over the Sahara Desert and Arabian Peninsula. In the meantime, the upper troposphere is predicted to become warmer because of the absorption by dust. These changes in temperature lead to a more stable atmosphere, which results in increases in surface humidity. The upward sensible and latent heat fluxes at the surface are reduced, largely balancing the surface energy loss caused by the backscattering and absorption of dust aerosol. Precipitation is predicted to decrease moderately on a global scale.

This paper describes a dynamical downscaling

simulation over China using the nested model system,

which consists of the modified Weather Research and

Forecasting Model (WRF) nested with the NCAR Community

Atmosphere Model (CAM). Results show that

dynamical downscaling is of great value in improving the

model simulation of regional climatic characteristics.

WRF simulates regional detailed temperature features

better than CAM. With the spatial correlation coefficient

between the observation and the simulation increasing

from 0.54 for CAM to 0.79 for WRF, the improvement in

precipitation simulation is more perceptible with WRF.

Furthermore, the WRF simulation corrects the spatial bias

of the precipitation in the CAM simulation.

The summer upper tropospheric temperature change and its association with atmospheric circulations and precipitation over the Asian Pacific region during the mid-Holocene have been addressed by using outputs from a coupled ocean atmosphere general circulation model performed as part of the second phase of the Paleoclimate Modeling Intercomparison Project. The simulated result shows the summer oscillation pattern similar to the present Asian Pacific oscillation (APO) existed in the mid‐Holocene. When there was a warming (cooling) upper troposphere over East Asia, a cooling (warming) upper troposphere occurred over the midlatitudes of the North Pacific. Compared to the modern climate, however, the simulated mid‐Holocene temperature in the upper troposphere was higher over East Asia and lower over the midlatitudes of the North Pacific, indicating a stronger summer APO in the mid‐Holocene. Corresponding to such a condition, the North Pacific was modeled to be dominated by a high-level cyclonic circulation difference and a low‐level anticyclonic circulation difference in the mid-Holocene relative to the present, which favored the subsidence of airflows and thus resulted in less precipitation in this region. Meanwhile, East Asia was simulated to be occupied by an anticyclonic circulation difference in the upper troposphere and a cyclonic circulation difference in th e lower troposphere. Accordingly, the ascending motion and the low‐level southerly wind strengthened in East Asia, leading to an increase of local precipitation in the mid‐Holocene. Therefore, the modeled mid‐Holocene climate suggests that the summer rainfall change over the Asian Pacific region may be a result of the strengthened APO in the upper troposphere.

This paper discusses projections of heavy rainfall events in China during the 21st century based on daily

precipitation data from the Fourth Assessment Report’s (AR4) Coupled General Circulation Models (CGCM). Results show

that all three experimental scenarios (scenarios A2, A1B, and B1) project consistent changes in frequency and intensity

of heavy rainfall at the end of 21st century. In the regions of Northeast China and North China, there are no significant

changes in frequency but there are remarkable increases in intensity of heavy rainfall, indicating that enhanced intensity

is the main contributor to increased ratios of heavy rainfall to total annual precipitation in these regions. In regions of the

lower reaches of Yangtze River and South China, increases in the amount of heavy rainfall are closely associated with

increased frequency and increased intensity. Projected frequencies of heavy rainfall at the end of 21st century increase by

30.9 ∼ 56.6% in the Yangtze River and 35.9 ∼ 50.2% in South China compared to the period of 1980–1999, and projected

intensities increase by 1.0 ∼ 5.7% and 2.8 ∼ 6.3%, respectively. Additionally, the ratios of heavy rainfall to total annual

precipitation increase by 2.3 ∼ 5.4% in the Yangtze River and 1.8 ∼ 3.8% in South China. The significant increases of

heavy rainfall ratios indicate that as the climate warms, heavy rainfall events are expected to increase at rates that are much

faster than increases in total precipitation amounts, indicating that China will experience increased amounts of flooding.

These results are substantially consistent among the three IPCC (Intergovernmental Panel on Climate Change) scenarios.

The increased probability of heavy rainfall events in China is closely connected with increased transportation of

water vapour from the Arabian Sea and the South China Sea. Additionally, atmosphere stratification has become

increasingly unstable, which has provided a favorable background for the initiation of heavy rainfall at the end of the

21st century.

The relationship between the boreal spring (or the austral autumn) Antarctic Oscillation (AAO) (March- April) and the West African summer monsoon (WASM) (June-September) is analyzed based on NCEP/NCAR reanalysis data. The results show that the linkage of the boreal spring AAO to the WASM exhibits decadal-scale variations: a strong connection between the two appears over the period 1985-2006 and a weak connection over the period 1970-1984. Further analysis indicates that such an unstable relationship between the two results from the modulation by ENSO events to a large extent.

A possible mechanism for the impacts of the boreal spring AAO on the WASM is also discussed. The variability of the boreal spring tropical South Atlantic sea surface temperature (SST) appears to serve as a bridge linking these two systems. The boreal spring AAO produces an anomalous SST over the tropical South Atlantic by exciting an equatorward Rossby wave train over the western Southern Hemisphere (SH). This AAO-related SST anomaly modulates the meridional gradient of moist static energy (MSE) between the Sahel and the Guinea-tropical Atlantic region in the boreal spring. The MSE gradient is of paramount importance for the changes from spring to summer in the West African monsoon because its relaxation along the seasonal cycle is linked to the northward excursion of the WASM system into the African continent. Therefore, an anomalous AAO-related MSE gradient can lead to anomalous Sahel rainfall in the early summer. When this rainfall occurs over the Sahel, the local positive soil moisture-rainfall feedback plays a crucial role in sustaining and prolonging this rainfall anomaly throughout the whole summer.

The Tropical Cyclone Genesis Potential Index (GPI) was employed to investigate possible impacts of

global warming on tropical cyclone genesis over the western North Paci¯c (WNP). The outputs of 20th cen-

tury climate simulation by eighteen GCMs were used to evaluate the models' ability to reproduce tropical

cyclone genesis via the GPI. The GCMs were found in general to reasonably reproduce the observed spatial

distribution of genesis. Some of the models also showed ability in capturing observed temporal variation.

Based on the evaluation, the models (CGCM3.1-T47 and IPSL-CM4) found to perform best when repro-

ducing both spatial and temporal features were chosen to project future GPI. Results show that both of

these models project an upward trend of the GPI under the SRES A2 scenario, however the rate of increase

di®ers between them.

This study examined the relationship between the boreal spring (April-May) Antarctic Oscillation (AAO) and the North American summer monsoon (NASM) (July-September) for the period of 1979-2008. The results show that these two systems are closely related. When the spring AAO was stronger than normal, the NASM tended to be weaker, and there was less rainfall over the monsoon region. The opposite NASM situation corresponded to a weaker spring AAO. Further analysis explored the possible mechanism for the delayed impact of the boreal spring AAO on the NASM. It was found that the tropical Atlantic sea surface temperature (SST) plays an important role in the connection between the two phenomena. The variability of the boreal spring AAO can produce anomalous SSTs over the tropical Atlantic. These SST anomalies can persist from spring to summer and can influence the Bermuda High, affecting water vapor transportation to the monsoon region. Through these processes, the boreal spring AAO exerts a significantly delayed impact on the amount of NASM precipitation. Thus, information about the boreal spring AAO is valuable for the prediction of the NASM.

Atmospheric circulation changes during boreal winter of the second half of the 20th century

exhibit a trend toward the positive polarity of both the Northern Hemisphere Annular Mode (NAM)

and the Southern Hemisphere Annular Mode (SAM). This has occurred in concert with other

trends in the climate system, most notably a warming of the Indian Ocean. This study explores

whether the tropical Indian Ocean warming played a role in forcing these annular trends. Five

different atmospheric general circulation models (AGCMs) are forced with an idealized, transient

warming of Indian Ocean sea surface temperature anomalies (SSTA), the results of which indicate

that the warming contributed to the annular trend in the Northern Hemisphere (NH) but offset the

annular trend in the Southern Hemisphere (SH). The latter result implies that the Indian Ocean

warming may have partly cancelled the influence of the stratospheric ozone depletion over the

southern polar area which itself forced a trend toward the positive phase of the SAM. Diagnosis of

the physical mechanisms for the annular responses indicates that the direct impact of the diabatic

heating induced by the Indian Ocean warming does not account for the annular response in the

extratropics. Instead, interactions between the forced stationary wave anomalies and transient

eddies is key for the formation of annular structures.

During the past decades the tropical Indo-Pacific Ocean has become warmer than before. Meanwhile, both Northern and Southern hemispheric polar vortices (NPV and SPV) exhibit a deepening trend in boreal winter. Although previous studies reveal that the tropical Indian Ocean Warming (IOW) favors intensifying NPV and weakening SPV, how the tropical Pacific Ocean Warming (POW) influences NPV and SPV is unclear. In this study, a comparative analysis is conducted through ensemble atmospheric general circulation model (AGCM) experiments. The results show that, for the northern hemisphere, the two warming exert opposite impacts in boreal winter, in that IOW intensifies NPV while POW weakens NPV. For the southern hemisphere, both IOW and POW warm the southern polar atmosphere and weaken SPV. A diagnostic analysis based on vorticity budget reveals that such an interhemispheric difference in influences from IOW and POW in boreal winter is associated with different roles of transient eddy momentum flux convergence between the hemispheres. Furthermore, this difference may be linked to different strength of stationary wave activity between the hemispheres in boreal winter.

Abstract An early warning system has been developed to predict

rainfall-induced shallow landslides over Java Island, Indonesia. The

prototyped early warning system integrates three major compo-

nents: (1) a susceptibility mapping and hotspot identification

component based on a land surface geospatial database (topo-

graphical information, maps of soil properties, and local landslide

inventory, etc.); (2) a satellite-based precipitation monitoring

system (http://trmm.gsfc.nasa.gov) and a precipitation forecasting

model (i.e., Weather Research Forecast); and (3) a physically based,

rainfall-induced landslide prediction model SLIDE. The system

utilizes the modified physical model to calculate a factor of safety

that accounts for the contribution of rainfall infiltration and partial

saturation to the shear strength of the soil in topographically

complex terrains. In use, the land-surface “where” information will

be integrated with the “when” rainfall triggers by the landslide

prediction model to predict potential slope failures as a function of

time and location. In this system, geomorphologic data are

primarily based on 30-m Advanced Spaceborne Thermal Emission

and Reflection Radiometer (ASTER) data, digital elevation model

(DEM), and 1-km soil maps. Precipitation forcing comes from both

satellite-based, real-time National Aeronautics and Space Admin-

istration (NASA) Tropical Rainfall Measuring Mission (TRMM),

and Weather Research Forecasting (WRF) model forecasts. The

system’s prediction performance has been evaluated using a local

landslide inventory, and results show that the system successfully

predicted landslides in correspondence to the time of occurrence of

the real landslide events. Integration of spatially distributed remote

sensing precipitation products and in-situ datasets in this prototype

system enables us to further develop a regional, early warning tool

in the future for predicting rainfall-induced landslides in Indonesia.

This paper uses Dobson spectrometer total

ozone data, Total Ozone Mapping Spectrometer (TOMS) data and radiosonde reports from Kunming, which is located in southwest China, from 1980 to 2008 to analyze the total ozone-climate relationship. The total ozone decadal long-term trend and abrupt change were studied using enhanced Dobson data whose missing data were amended by the TOMS data. Stepwise linear regression was used for the selection of the key factors that influence total ozone, including temperatures, geopotential heights, depressions of the dew point, wind velocities, and total solar radiation. The relationship between the selected factors and total ozone was analyzed using the methods of stepwise regression and partial least squares regression (PLSR). Results showed that although the PLSR method was slightly better and more reasonable to study the relationship than stepwise regression, while the two regression results were only slightly different. It was also suggested that local climate, especially local circulation and temperature, were important for the variations in total ozone, and the local climate could almost linearly explain 80% of

the variance of total ozone. The relationship also indicated that the abrupt change of total ozone in the year 1994 may be related to abrupt local climate change.

In the present study, datasets derived from twelve coupled ocean–atmosphere general circulation models (OAGCMs) in the Paleoclimate Modelling Intercomparison Project phase two were used to analyze the East Asian summer climate during the mid-Holocene (about 6,000 calendar years ago). On the whole, the OAGCMs reproduced warmer and wetter summer climate conditions in East Asia during the mid-Holocene. The multi-model ensemble showed that in East Asia, the regionally-averaged summer surface air temperature (SAT) increased by 0.89°C, summer precipitation was 5.8% higher, and an obviously strengthened southerly wind corresponded to a strong summer monsoon in the mid-Holocene when compared to preindustrial levels. The data-model comparison in China reveals a good agreement between the OAGCMs’ results and the reconstructed changes in the summer SAT in East China during the mid-Holocene. In North China, the simulated SAT anomalies are 0.5°C lower overall than reconstruction. In contrast, the OAGCMs fail to capture the strongest warming in the southern Qinghai-Tibetan Plateau. On the other hand, the simulated precipitation agrees well with proxy data except for in the central parts of China, where the simulated summer precipitation disagrees in sign with reconstruction. In addition, there is a large spread among the simulations, particularly over and around the Qinghai-Tibetan Plateau, and inter-model discrepancies are larger for precipitation than for SAT as a whole.

This study documents the decadal changes of the summer precipitation in East China, with increased rainfall in the Huang-Huai River region (HR) and decreased in the Yangtze River region (YR) during 2000–2008 in comparison to 1979–1999. The main features of the atmospheric circulation related to the increased precipitation in the HR are the strengthened ascending motion and slightly increased air humidity, which is partly due to the weakened moisture transport out of the HR to the western tropical Pacific (associated with the weakened westerly over East Asia and the warming center over the Lake Baikal). The rainfall decrease in the YR is related to the weakened ascending motion and reduced water vapor content, which is mainly related to the weakened southwesterly moisture flux into the YR (associated with the eastward recession of the Western Pacific Subtropical High). The global sea surface temperature (SST) also shows significant changes during 2000–2008 relative to 1979–1999. The shift of the Pacific decadal oscillation (PDO) to a negative phase probably induces the warming over the Lake Baikal and the weakened westerly jet through the air-sea interaction in the Pacific, and thus changes the summer precipitation pattern in East China. Numerical experiments using an atmospheric general circulation model, with prescribed all-Pacific SST anomalies of 2000–2008 relative to 1979–1999, also lend support to the PDO’s contribution to the warming over the Lake Baikal and the weakened westerlies over East China.

A new empirical approach for the seasonal prediction of annual Atlantic tropical storm number (ATSN) was developed using precipitation and 500 hPa geopotential height data from the preceding January−

February and April−May. The 2.5°×2.5° resolution reanalysis data from both the US National Center for Environmental Prediction/the National Center for Atmospheric Research (NCEP/NCAR) and the European Center for Medium-Range Weather Forecasting (ECMWF) were applied. The model was cross-validated using data from 1979−2002. The ATSN predictions from the two reanalysis models were correlated with the observations with the anomaly correlation coefficients (ACC) of 0.79 (NCEP/NCAR) and 0.78 (ECMWF) and the multi-year mean absolute prediction errors (MAE) of 1.85 and 1.76, respectively. When the predictions of the two models were averaged, the ACC increased to 0.90 and the MAE decreased to 1.18, an exceptionally high score. Therefore, this new empirical approach has the potential to improve the operational prediction of the annual tropical Atlantic storm frequency.

Based on the physical-mathematical considerations, the authors discussed the object of the short-term climate prediction. The short-term climate prediction has extremely important potential benefit for the economy and society, but is a very difficult scientific systematic work. Traditionally, the anomaly of a variable to its climatology has been used as the object of the shortterm climate prediction. However, this approach does not necessarily contain physical-mathematical robustness. Considering that the current climate prediction skill, based on the above approach, is quite limited, the authors proposed another approach, using the interannual increment of a variable as the predicting object. The authors also provides discussion on this approach from the physical-mathematical considerations, and validation of this approach based on a climate model prediction experiment.

A new prediction approach for summer (June–August) rainfall in China was designed by considering both preceding observations and numerically predicted summer rainfall through a multivariate linear regression analysis. First, correlation analyses revealed close relationships between summer rainfall in parts of China with the Antarctic Oscillation (AAO), the Arctic Oscillation (AO), and sea surface temperatures (SSTs) in the preceding winter (December–February). The Huang-Huai Valley, two subregions of the Jiang-Huai Valley, the southern Yangtze River, south China, and southeastern Xinjiang were then chosen as targets for their regional

climate characteristics. Following this, an extraseasonal (one season in advance) regression prediction model for

regionally averaged summer rainfall was constructed by using these three climate factors and a 3-month leadtime forecast of summer rainfall, undertaken by an atmospheric general circulation model (GCM) forced by

observed SSTs, as predictors region by region. To improve the accuracy of prediction, the systematic error between the original regression model’s results and its observational counterparts, averaged for the last 10 yr,was corrected. Using this new approach, real-time prediction experiments and cross-validation analyses were performed

for the periods 2002–07 and 1982–2007, respectively. It was found that the new prediction approach was more skillful than the original or corrected GCM prediction alone in terms of sign, magnitude, and interannual variability of regionally averaged summer rainfall anomalies in all regions. The preceding observations were the

major source of the prediction skill of summer rainfall in each region, and the GCM predictions added additional prediction skill in thewestern Jiang-HuaiValley and southeastern Xinjiang, in both of which the GCM prediction was used as a predictor.

The statistical spatial‐temporal features of the intense snowfall event (ISE) in China

are investigated over the period of 1962–2000. The results indicate that eastern China,

northern Xinjiang, the eastern Tibetan plateau, and northeastern China are four key regions for the ISE, with more frequency and strong variability. Annual cycle analysis shows the ISE exhibits a unimodal distribution with maximum frequency at winter months for eastern China, a bimodal distribution with maximum frequency at early winter and spring months for northern Xinjiang and northeastern China, and a bimodal distribution with maximum frequency at autumn and spring months for the eastern Tibetan plateau. Linear trend analysis indicates that in the last 39 years, the ISE exhibits a decreasing trend for eastern China and an increasing trend for northern Xinjiang and the eastern Tibetan plateau. The linear trend of the ISE is weak over northeastern China. Based on the simulations of the most recent and comprehensive climate models in the 20th century run, the performance of the current climate models in simulating the Chinese ISE is investigated. The results indicate that, of the 20 models, there are four models that can reasonably reproduce the spatial‐temporal features of the Chinese ISE. Based on these four models’ simulation for the 21st century under A1B and A2 scenarios, the future variability of the Chinese ISE is projected. It is found that global warming will cause the ISE frequency over southern China to decrease, while the ISE over northern China will initially increase and then decrease.

The relationship between the boreal winter (December, January, February) Aleutian Low (AL) and the simultaneous Australian summer monsoon (ASM) is explored in this study. A significant correlation is found between the North Pacific index (NPI) and ASM index, the bulk of which is attributed to the significant correlation after late 1970s. Significant differences in precipitation and outgoing long-wave radiation between typical negative and positive NPI years appear over the ASM area. A regression analysis of the circulation pattern against the NPI during the three months is performed separately. We propose that the NPI is related with the ASM circulation possibly through the changes in the upper level westerly jet. In a typical negative NPI (strong Aleutian Low) year, the jet is greatly reinforced and the anomalous anticyclonic circulation to the south is thus excited, from which the easterly wind anomalies °owing into the ASM region emanate. Further, strong sinking motion over the northern entrance region of the jet is enhanced, and the local Hadley circulation anomaly between the ASM region and the coast of East Asia is strengthened. In this way, anomalous upward motion over the ASM area can thus be strengthened, and the convective activity intensified. Then the monsoon rainfall over ASM area is increased. An \asymmetric" connection between AL and the monsoon is found in this study.

This study evaluates the fidelity of Arctic and Antarctic oscillations (AO and AAO for short, respectively)in the coupled general circulation models participating in the Fourth Assessment Report of Intergovernmental Panel on Climate Change (IPCC AR4). The AO and AAO during 1970-1999 in 24 models are analyzed and compared with that in ERA-40 and NCEP-1. Models' performance is seasonally dependent, with best reproducibility of both spatial structure and trend in winter. In most models, the spatial pattern and temporal trend of AAO during this period are more delicately simulated than AO. After picking out models with better performance according to the Taylor diagram, we find that their ensemble mean can obviously improve models' reproducibility. The AO and AAO in the Special Report on Emission Scenarios (SRES)A1B Projection during the 21st century are also briefiy analyzed. The results reveal that both the AO and AAO indices keep increasing during 1970-2099, with a steadier pace of AO than AAO. The spatial difference of sea level pressure between 2060-2089 and 1970-1999 shows decreased values in polar regions,and increased values in midlatitudes. The results manifest that the ozone recovery during the mid 21st century may not weaken such a trend.

We present a model for predicting summertime surface air temperature in Northeast China (NESSAT)

using a year-to-year incremental approach. The predicted value for each year's increase or decrease of

NESSAT is added to the observed value within a particular year to yield the net forecast NESSAT. The

seasonal forecast model for the year-to-year increments of NESSAT is constructed based on data from 1975{

2007. Five predictors are used: an index for sea ice cover over the East Siberian Sea, an index for central

Paci¯c tropical sea surface temperature, two high latitude circulation indices, as well as a North American

pressure index. All predictors are available by no later than March, which allows for compilation of a seasonal

forecast with a two-month lead time. The prediction model accurately captures the interannual variations

of NESSAT during 1977{2007 with a correlation coe±cient between the predicted and observed NESSAT of

0.87 (accounting for 76% of total variance) and a mean absolute error (MAE) of 0.3±C. A cross-validation

test during 1977{2008 demonstrates that the model has good predictive skill, with MAE of 0.4±C and a

correlation coe±cient between the predicted and observed NESSAT of 0.76.

This paper presents a year-by-year incremental approach to forecasting the Atlantic named storm frequency (ATSF) for the hurricane season (1 June–30 November). The year-by-year increase or decrease in the ATSF is first forecasted to yield a net ATSF prediction. Six key predictors for the year-by-year increment in the number of Atlantic named tropical storms have been identified that are available before 1 May. The forecast model for the year-by-year increment of the ATSF is first established using a multilinear regression method based on data taken from the years 1965–99, and the forecast model of the ATSF is then derived. The prediction model for the ATSF shows good prediction skill. Compared to the climatological average mean absolute error (MAE) of 4.1, the percentage improvement in theMAEis 29% for the hindcast period of 2004–09 and 46% for the cross-validation test from 1985 to 2009 (26 yr). This work demonstrates that the year-by-year incremental approach has the potential to improve the operational forecasting skill for the ATSF.

We have developed a Global Transport Model of Dust (GMOD) within a general circulation model, using comprehensive parameterizations of the emission and deposition processes from Wang et al. (2000). These parameterizations are modified to match the surface conditions and meteorological fields of the climate model. A 20-year simulation from the dust model predicts an average dust emission of 1935 ± 51 Tg a-1 and a global dust burden of 27.8 ± 0.8 Tg for particles whose radii are smaller than 10 μm. Comparisons with observations show that the GMOD reproduces reasonably well dust concentrations (mean bias MB of -0.67 μg m-3, normalized mean bias NMB of -8.0%, correlation coefficient of 0.96 at 18 sites), logarithmic total deposition (-0.62 g m-2 a−1, -36.0%, 0.84 at 251 sites), and aerosol optical thickness (-0.04, -26.7%, 0.80 at 16 sites). The simulated dust particle size distribution is consistent with observations; both have a volume median radius in the range 1.0–4.0 μm. We examine the temporal variation of dust transport on different timescales. The simulated interannual variability is small, but the seasonal variation is quite large in the Sahara Desert and central Asia. We pay special attention to the diurnal variation of dust; both observations and simulations show that dust mobilization is more active during the local daytime than nighttime. On a global and annual mean basis, the simulated ratio of the daytime maximum uplift to the nighttime minimum is 75. Both the dust burden and dry deposition of dust show a similar diurnal cycle peaking in the late afternoon.

The old radiation scheme in IAP9L-AGCM is replaced by a new one from NCAR CCM3 codes. And the effects of such modification are evaluated in details. It shows that there are many improvements in the simulated radiation fields by the new version of IAP9L-AGCM, especially some net radiation fields on the surface. As a result, there is a prevalent enhancement of the atmospheric temperature in the new version. Other fields, such as sea level pressure, surface air temperature, geopotential height, wind field, precipitation, specific humidity and so on, show some corresponding changes, though the magnitudes are not large. The evaluation results put forward the requirement of a further improvement of the IAP9L-AGCM.

本文利用一个耦合气候模式执行的一组淡水试验，研究了在北大西洋高纬度淡水注入量增高的情景下东亚夏季风的响应及机制，并与其它耦合模式所做的淡水试验的结果做了对比。 研究显示随着北大西洋高纬度海域淡水注入量的增多，北大西洋经圈环流减弱，导致北大西洋海表变冷，从而使得北美区域海平面气压升高，与之对应的是赤道热带东太平洋海表增强的穿过赤道的东北风，进而使得该海域内冷水上翻增强，海表散热加大，导致海表温度降低，其结果是赤道以北热带东太平洋Hadley环流减弱， 同时赤道以北热带Walker环流增强及上升支东移，东亚大陆沿岸出现气旋性风场异常，最终导致东亚夏季季风区降水减弱。另外通过与其它淡水试验的比较，北大西洋淡水试验中东亚夏季风的强弱变化受北大西洋高纬度淡水注入量大小的影响。

利用1957~ 2006 年50 年的地温、气温和降水资料, 分析了中国区域春季地气温差的分布特征, 并利用线性

相关和奇异值分解方法对春季地气温差与夏季降水的关系进行了探讨。结果表明: 中国大陆春季地气温差分布与

地势大体吻合。在长江中下游为涝年时, 青藏高原春季的地气温差偏大, 而黄淮流域的春季地气温差偏小, 与青藏

高原相反。青藏高原春季的地气温差与长江中下游地区夏季降水存在显著的正相关, 即春季青藏高原地区地气温

差较大( 小) , 长江流域的夏季降水会比正常年份偏多( 少) , 青藏高原春季地气温差对长江中下游夏季降水有一定

的指示意义。

The mid-Holocene (6ka B.P.) is a typical interglacial period in which climate was largely different from the present day. By far there have been a number of mid-Holocene climate simulations. However, those simulations were completed mainly by atmospheric general circulation models and few by coupled ocean-atmosphere general circulation models. Moreover, the simulations focused on the summer mean climate status while paid less attention to the evolution of the East Asian monsoon. Therefore, the present study is motivated to investigate the seasonal evolution of the southwesterly wind climate over eastern China in the mid-Holocene, through analyzing the simulation result of an ocean-atmosphere coupled model named CCSM3.

The results show that the southerly wind during 6ka B.P. begins earliest over eastern China within 20°-25°N in January. It gradually strengthens afterwards and switches to the northerly wind in autumn. Concurrent with the development of its intensity, the southerly wind extends northward and southward from spring to summer. Similar to the change of the southerly wind direction, there is a reversal of the zonal wind direction over eastern China as well. The westerly wind during 6ka B.P. appears over eastern China within 23°-34°N in January, and then reinforces gradually. It shifts northward during June to August and is substituted by the easterly wind in September. To the north of 34°N, there is no seasonal reversal of the zonal wind direction, with the westerly wind blowing all year round. Such features resemble those of the present climate. However, there also exists significant difference between 6ka B.P. and the present, especially in summer. Compared to the present climate, the onset time of the strong southerly wind over eastern China during 6ka B.P. seems to be a litter later. Furthermore, the southwesterly wind over eastern China is much stronger and its extension is further northward during the summer time. The existence of the difference between 6ka B.P. and the present can be attributed to the changes of the land-sea thermal contrast，the southwest vortex and western Pacific subtropical high. In comparison with the counterpart of the present day, the large-scale thermal difference between the East Asian continent and the western Pacific as well as the intensity of the southwest vortex and the western Pacific subtropical high during 6ka B.P. is obviously stronger, favoring the increase of the local southwesterly wind. Besides, the western Pacific subtropical high located to the north makes the southwesterly wind expand further northward during 6ka B.P.. In addition, accompanied with the evolution of the southwesterly wind during 6ka B.P., the low-level convergence gradually intensifies and marches northward from winter to summer, resulting in the increase of the local rainfall and the shift of the major rain belt. Nevertheless, the preliminary result is just obtained from a coupled ocean-atmosphere general circulation model. Ensemble analysis based on more coupled ocean-atmosphere general circulation models are needed in the future work. It is also expected to do further study with more integrated geologic data and high-resolution regional climate models to simulate 6ka B.P. climate.

Projected changes in summer precipitation characteristics in China during the 21st century are assessed using the monthly precipitation outputs of the ensemble of three “best” models under the Special Report on Emissions Scenarios (SRES) A1B, A2, and B1 scenarios. The excellent reproducibility of the models both

in spatial and temporal patterns for the precipitation in China makes the projected summer precipitation

change more believable for the future 100 years. All the three scenarios experiments indicate a consistent

enhancement of summer precipitation in China in the 21st century. However, the projected summer precipitation

in China demonstrates large variability between sub-regions. The projected increase in precipitation in South China is significant and persistent, as well as in North China. Meanwhile, in the early period of the 21st century, the region of Northeast China is projected to be much drier than the present. But, this situation changes and the precipitation intensifies later, with a precipitation anomaly increase of 12.4%–20.4% at the end of the 21st century. The region of the Xinjiang Province probably undergoes a drying trend in the future 100 years, and is projected to decrease by 1.7%–3.6% at the end of the 21st century. There is

no significant long-term change of the projected summer precipitation in the lower reaches of the Yangtze

River valley. A high level of agreement of the ensemble of the regional recipitation change in some parts

of China is found across scenarios but smaller changes are projected for the B1 scenario and slightly larger changes for the A2 scenario.

This paper investigates the variability of the break-up dates of the rivers in Northeast China from their icebound states for the period of 1957–2005 and explores some potential explanatory mechanisms. Results show that the break-up of the two major rivers (the Heilongjiang River and Songhuajiang River)

was about four days earlier, and their freeze-up was about 4–7 days delayed, during 1989–2005 as compared

to 1971–1987. This interdecadal variation is evidently associated with the warming trend over the past 50 years. In addition, the break-up and freeze-up dates have large interannual variability, with a standard deviation of about 10–15 days. The break-up date is primarily determined by the January–February–March

mean surface air temperature over the Siberian-Northeast China region via changes in the melting rate,

ice thickness, and snow cover over the ice cover. The interannual variability of the break-up date is also

significantly connected with the Northern Annular Mode (NAM), with a correlation coefficient of 0.35–0.55 based on the data from four stations along the two rivers. This relationship is attributed to the fact that the NAM can modulate the East Asian winter monsoon circulation and Siberian-Northeast China surface

air temperature in January–February–March.

A significant correlation between the boreal spring Antarctic Oscillation (AAO) and the Yangtze River valley

summer rainfall (YRVSR) has been found in previous studies, although the mechanisms that might lead to such far-reaching

teleconnection remain unresolved. In this study, one of possible mechanisms responsible for the co-variability of the boreal spring AAO and the YRVSR is proposed. It follows that the convection activity over the region of the Maritime Continent serves as a bridge linking the boreal spring AAO and the YRVSR. This physical process can be described schematically as follows: during the boreal spring, a positive-phase (negative-phase) AAO is concurrent with a strong (weak) convection activity over the region of the Maritime Continent via anomalous meridional circulations along the central South Pacific

and two meridional teleconnection wave train patterns, with one over the southern Indian Ocean at the lower level and the other along the central South Pacific at the upper level. Thereafter, the anomalous convection propagates northward along the seasonal cycle, and then changes the western Pacific subtropical high in the following seasons, consequently impacting

on the summer rainfall in the Yangtze River valley.

Recent observational study has shown that the southern center of the summer North Atlantic Oscillation (SNAO) was located farther eastward after the late 1970s compared to before. In this study, the cause for this phenomenon is explored. The result shows that the eastward shift of the SNAO southern center after

the late 1970s is related to the variability of the Mediterranean-Black Sea (MBS) SST. A warm MBS SST can heat and moisten its overlying atmosphere, consequently producing a negative sea level pressure (SLP) departure over the MBS region. Because the MBS SST is negatively correlated with the SNAO, the

negative SLP departure can enhance the eastern part of the negative-phase of the SNAO southern center, consequently producing an eastward SNAO southern center shift. Similarly, a cold MBS SST produces an eastward positive-phase SNAO southern center shift. The reason for why the MBS SST has an impact on the SNAO after the late 1970s but why it is not

the case beforehand is also discussed. It is found that this instable relationship is likely to be attributed to

the change of the variability of the MBS SST on the decadal time-scale. In 1951–1975, the variability of

the MBS SST is quite weak, but in 1978–2002, it becomes more active. The active SST can enhance the interaction between the sea and its overlying atmosphere, thus strengthening the connection between the MBS SST and the SNAO after the late 1970s. The above observational analysis results are further confirmed

by sensitivity experiments.

A snowstorm deposited record2breaking snowfall over the northeastern parts of China on March 3-5, 2007, resulting in

severe disasters and heavy losses. The objective of this study is to explore the possible mechanism responsible for this extreme event by analyzing the atmospheric circulation anomalies prior to and during the event. The results show that there had been persistent strong

anomalous Arctic Oscillations, Antarctic Oscillations, Eurasian teleconnection pattern, and North Pacific Oscillations in about two weeks before the event. Those anomalous atmospheric circulations stimulated the strong anomalous southerlies along the east coastal

regions of China, which persistently transferred the warm and wet air to the northeastern areas of China, thus raising the moisture content and air temperature there and providing proper warm and wet conditions for the occurrence of the extreme snowstorm event. When the atmospheric general circulation changed in early March, the strong cold air from the high latitudes met the warm air over

the northeastern China, resulting in a remarkably cold front and associated strong snowfall and low temperature in that region.

The results of this study imply that the anomalous atmospheric circulation and the cumulative moisture condition in the forecast region in the early stage should be fully considered, which is helpful to the improvement of rainfall forecast, especially the heavy rainfall forecast.

Recent observational studies have shown that the southern center of the summer North Atlantic Oscillation (SNAO) shifted eastward after the late 1970s. In this study, this phenomenon and its causes are further explored. It is found that the decadal spatial shift of the SNAO southern center is related to the decadal variability of the tropical Atlantic sea surface temperature (TASST). In the past half century, the TASST experienced an abrupt change around the late 1970s, with a rapid warming in the recent 2 decades. Thus in the period after the late 1970s when the TASST is relatively warmer, the TASST released more energy into the atmosphere, then stimulated strong convection over the tropical Atlantic, and further excited anomalous wave-like patterns. This strengthened the circulation in the region of the Mediterranean Sea, namely the east part of the SNAO southern center, consequently leading to an eastward shift of the SNAO southern center. Meanwhile, in the period before the late 1970s when the TASST is relatively cooler, the TASST released less energy into the atmosphere, so its impact on the overlying atmosphere was significantly weakened and confined to the lower-level atmosphere of the tropical Atlantic. Thus the TASST possibly did not influence the variability of the SNAO southern center, and the SNAO pattern exhibited a traditional distribution with two centers over the North Atlantic.

This study investigates the relationship between the summer North Atlantic Oscillation (SNAO) and the

simultaneous Northern Hemisphere (NH) land surface air temperature (SAT) by using the Climate Research Unit (CRU) data. The results show that the SNAO is related to NH land SAT, but this linkage has varied on decadal timescales over the last 52 years, with a strong connection appearing after the late 1970s, but a

weak connection before. The mechanism governing the relationship between the SNAO and NH land SAT is discussed based on the NCEP/NCAR reanalysis data. The results indicate that such a variable relationship may result from changes of the SNAO mode around the late 1970s. The SNAO pattern was centered mainly

over the North Atlantic before the late 1970s, and thus had a weak influence on the NH land SAT. But after the late 1970s, the SNAO pattern shifted eastward and its southern center was enhanced in magnitude and extent, which transported the SNAO signal to the North Atlantic surrounding continents and even to

central East Asia via an upper level wave train along the Asian jet.

Studies on the influences of climate change on biogeochemical cycles and on the key vulnerabilities and the risk from climate change suggest that annual surface temperature rise of 1℃, 2℃ and 3℃ above the present level would lead to changes in extreme weather and climate events, food production, fresh water resources, biodiversity, human mortality, etc. Here two sets of simulations as performed with seventeen atmosphere-ocean general circulation models (AOGCMs) for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4), i.e. the model outputs from the 20th Century Climate in Coupled Models (20C3M) and from the Special Report on Emissions Scenarios (SRES) emission scenarios B1, A1B and A2, are used to analyze spatial and temporal characteristics of the above values in China over the 21st century. The results indicate that the rate of warming varies from region to region. The above values are reached much later (earlier) when emission amount is lower (higher), and spread of the time when the lower (higher) value is exceeded is narrower (wider) among the three scenarios. As far as the spatial pattern is concerned, the above values are crossed much earlier in northern China and the Tibetan Plateau with respect to the Yangtze-Huaihe River Valley and South China.

A unified chemistry-aerosol-climate model is applied in this work to compare climate responses to changing

concentrations of long-lived greenhouse gases (GHGs, CO2, CH4, N2O), tropospheric O3, and aerosols

during the years 1951–2000. Concentrations of sulfate, nitrate, primary organic carbon (POA), secondary

organic carbon (SOA), black carbon (BC) aerosols, and tropospheric O3 for the years 1950 and 2000 are

obtained a priori by coupled chemistry-aerosol-GCM simulations, and then monthly concentrations are interpolated

linearly between 1951 and 2000. The annual concentrations of GHGs are taken from the IPCC

Third Assessment Report. BC aerosol is internally mixed with other aerosols. Model results indicate that the

simulated climate change over 1951–2000 is sensitive to anthropogenic changes in atmospheric components.

The predicted year 2000 global mean surface air temperature can differ by 0.8◦C with different forcings.

Relative to the climate simulation without changes in GHGs, O3, and aerosols, anthropogenic forcings of

SO2− 4 , BC, BC+SO2− 4 , BC+SO2− 4 +POA, BC+SO2− 4 +POA+SOA+NO−3 , O3, and GHGs are predicted to

change the surface air temperature averaged over 1971–2000 in eastern China, respectively, by −0.40◦C,

+0.62◦C, +0.18◦C, +0.15◦C, −0.78◦C, +0.43◦C, and +0.85◦C, and to change the precipitation, respectively,

by −0.21, +0.07, −0.03, +0.02, −0.24, −0.08, and +0.10 mm d−1. The authors conclude that all

major aerosols are as important as GHGs in influencing climate change in eastern China, and tropospheric

O3 also needs to be included in studies of regional climate change in China.

The influence of the Atlantic Multidecadal Oscillation (AMO) on Asian monsoonal

climate in all four seasons is investigated by comprehensive observational analyses

and ensemble experiments with atmospheric general circulation models (AGCMs). Three

AGCMs are forced by prescribed climatological seasonal cycle of sea surface temperature

(SST) or with additional SST anomalies representing the warmth phase of the AMO.

The results in both the observations and the models consistently suggest that the warm

AMO phase gives rise to elevated air temperatures in East Asia and northern India but

decreased air temperatures in much of central-southern India in all four seasons. This

positive AMO anomaly also causes more rainfall in central and southern India in every

season, particularly in summer and fall. In contrast, the sign of AMO influences on East

Asian rainfall is season-dependent: in southeastern China, it induces increased rainfall

in summer but suppressed rainfall in autumn. It is suggested that these AMO influences

are realized by warming Eurasian middle and upper troposphere in all four seasons,

resulting in weakened Asian winter monsoons but enhanced summer monsoons.

Furthermore, the formation of the troposphere heating anomaly may be related to the wave

guidance mechanism associated with the Asian upper jet.

During the past decades, concurrent with global warming, most of global oceans, particularly the tropical Indian Ocean, have become warmer. Meanwhile, the Southern Hemispheric stratospheric polar vortex (SPV) exhibits a deepening trend. Although previous modeling studies reveal that radiative cooling effect of ozone depletion plays a dominant role in causing the deepening of SPV, the simulated ozone-depletion-induced SPV deepening is stronger than the observed. This suggests that there must be other factors canceling a fraction of the influence of the ozone depletion. Whether the tropical Indian Ocean warming (IOW) is such a factor is unclear. This issue is addressed by conducting ensemble atmospheric general circulation model (AGCM) experiments. And one idealized IOW with the amplitude as the observed is prescribed to force four AGCMs. The results show that the IOW tends to warm the southern polar stratosphere, and thus weakens SPV in austral spring to summer. Hence, it offsets a fraction of the effect of the ozone depletion. This implies that global warming will favor ozone recovery, since a warmer southern polar stratosphere is un-beneficial for the formation of polar stratospheric clouds (PSCs), which is a key factor to ozone depletion chemical reactions.

East Asia experienced a significant interdecadal climate shift around the late 1970s, with more floods in the valley of the Yangtze River of central-eastern China and more severe drought in North China since then.Whether global SST variations have played a role in this shift is unclear. In the present study, this issue is investigated by ensemble experiments of an atmospheric general circulation model (AGCM), the GFDL AM2, since one validation reveals that the model simulates the observed East Asian Summer Monsoon (EASM) well. The results suggest that decadal global SST variations may have played a substantial role in this climate shift. Further examination of the associated atmospheric circulation shows that these results are physically reasonable.

A new scheme is developed to improve the seasonal prediction of summer precipitation in the East Asian and western Pacific region. The scheme is applied to the Development of a European Multimodel Ensemble System for Seasonal to Interannual Prediction (DEMETER) results. The new scheme is designed to consider both model predictions and observed spatial patterns of historical ‘‘analog years.’’ In this paper, the anomaly

pattern correlation coefficient (ACC) between the prediction and the observation, as well as the root-meansquare error, is used to measure the prediction skill. For the prediction of summer precipitation in East Asia and the western Pacific (0–40N, 80–130E), the prediction skill for the six model ensemble hindcasts for the years of 1979–2001 was increased to 0.22 by using the new scheme from0.12 for the original scheme. Allmodels

were initiated in May and were composed of nine member predictions, and all showed improvement when applying the newscheme.The skill levelsof the predictions for the sixmodels increased from0.08, 0.08, 0.01, 0.14, -0.07, and 0.07 for the original scheme to 0.11, 0.14, 0.10, 0.22, 0.04, and 0.13, respectively, for the new scheme.

This paper presents a new approach for forecasting the typhoon frequency of the western North Pacific (WNP). The year-to-year increase or decrease in typhoon frequency is first forecasted to yield a net typhoon frequency prediction. Five key predictors for the year-to-year increment in the number of typhoons in the WNP have been identified, and a forecast model is established using a multilinear regression method based

on data taken from 1965 to 2001. Using the forecast model, a hindcast of the typhoon frequency of the WNP during 2002–07 is made. The model exhibited a reasonably close fit for the period 1965–2007, including the

larger anomalies in 1997 and 1998. It also accounted for the smaller variability of the typhoon frequency of the WNP during the validation period 2002–07 with an average root-mean-square error (RMSE) of 1.3 (2.85)

during 2002–07 (1965–2001).The cross-validation test of the prediction model shows that the new approach and the prediction model demonstrate better prediction skill when compared to the models established based

on typhoon frequency rather than the typhoon frequency increment. Thus, this new approach has the potential to improve the operational forecasting skill for typhoon frequency in the WNP.

This paper investigates the variability of the break-up dates of the rivers in Northeast China from their icebound states for the period of 1957–2005 and explores some potential explanatory mechanisms. Results show that the break-up of the two major rivers (the Heilongjiang River and Songhuajiang River)was about four days earlier, and their freeze-up was about 4–7 days delayed, during 1989–2005 as compared to 1971–1987. This interdecadal variation is evidently associated with the warming trend over the past 50 years. In addition, the break-up and freeze-up dates have large interannual variability, with a standard deviation of about 10–15 days. The break-up date is primarily determined by the January–February–March mean surface air temperature over the Siberian-Northeast China region via changes in the melting rate, ice thickness, and snow cover over the ice cover. The interannual variability of the break-up date is also significantly connected with the Northern Annular Mode (NAM), with a correlation coefficient of 0.35–0.55 based on the data from four stations along the two rivers. This relationship is attributed to the fact that the NAM can modulate the East Asian winter monsoon circulation and Siberian-Northeast China surface air temperature in January–February–March.

The Intergovernmental panel for Climate Change(IPCC) Report Series issued stronger and stronger conclusion that the climate change in the 20~(th) century is very much likely the largest climate change in recent 1000 years and warming the 20~(th) century is attributed to the green house gases increase. Recent studies suggest that the climate change is accelerated and the future climate change may well be larger than previously projected. However, there are opposite opinions as well both abroad and domestic. This article will discuss the issue of will the future climate change in China lager or smaller than projected. Our analyses will based on the climate model behavior in simulating the last glacial maximum and the mid-Holocene climates, as well as the recent changes in temperature, sea level, green house gases, mountain glaciers, and so on. All these information seems to lead to a conclusion that the future climate change in China might larger than projected by the state-of-the-art climate models. In order to better adjust to the climate change, recognizing the key vulnerable regions to climate change is essential. The paper suggests several key vulnerable regions, including the source region of the three major rivers (Yangtze River,Yellow River, and Lantsang River) ,the Central North China, North East China, North West China, and South Eastern China. Key issues for the source region of the three rivers include the fast melting of the mountain glaciers in the Tibetan Plateau region and the associated water cycle and supply to source region of the river. In the north part of the country, precipitation change and the related water resource change are the key concerns, particular for the Central North China. In the South Eastern China, we should pay more attention to the variation of climate extreme,including the flood,typhoon landfalling,and heat waves.

Recent observational studies have shown that the southern center of the summer North Atlantic Oscillation (SNAO) shifted eastward after the late 1970s. In this study, this

phenomenon and its causes are further explored. It is found that the decadal spatial shift of the SNAO southern center is related to the decadal variability of the tropical Atlantic sea surface temperature (TASST). In the past half century, the TASST experienced an abrupt change around the late 1970s, with a rapid warming in the recent 2 decades. Thus in the period after the late 1970s when the TASST is relatively warmer, the TASST released more energy into the atmosphere, then stimulated strong convection over the tropical Atlantic, and further excited anomalous wave-like patterns. This strengthened the circulation in the region of the Mediterranean Sea, namely the east part of the SNAO southern center, consequently leading to an eastward shift of the SNAO southern center. Meanwhile, in the period before the late 1970s when the TASST is relatively cooler, the TASST released less energy into the atmosphere, so its impact on the overlying atmosphere was significantly weakened and confined to the lower-level atmosphere of the tropical Atlantic. Thus the TASST possibly did not influence the variability of the SNAO southern center, and the SNAO pattern exhibited a traditional distribution with two centers over the North Atlantic.

We investigated aerosol hygroscopic growth property and its influence on scattering coefficient using M9003 nephelometers in coupling with humidity controlled inlet system at a rural site near Beijing mega-city from 24 April to 15 May 2006. Inlet relative humidity was controlled in an increasing range of 40%–90% while aerosol hygroscopic growth factor of scattering coefficient, f(RH=80%) as ratio of scattering coefficient at RH=80% to "dry" scattering coefficient (RH<40%) varied in a range of 1.07–2.35 during the measurement. Further analysis indicated that under dust episode, measured f(RH=80%) is 1.2±0.02, and estimated periodic mean value of f(RH=80%) was 1.31±0.03 under clean periods; during urban pollution periods, the aerosol displayed relative strong water absorbing properties with f(RH=80%) of about 1.57±0.02. An examination of chemical composition of daily filter samples highlighted that aerosol hygroscopicity was generally depressed with the increasing ratio of organic matter (OMC)/ammonium sulfate (AS) in particle mass, similar with the results of many previous studies. However, a special case with high value of f(RH=80%)=2.21 and high OMC/AS ratio was also observed, this exception reflected physico-chemical particularities of organic matter and its complex interaction with other compounds during this episode.

Mineral dust is usually transported long distances in the lower troposphere. There are examples of Asian dust being transported across the Pacific Ocean1, 2, 3, 4, 5, 6, 7, and traces of Asian dust have also been found in ice and snow cores in Greenland8 and the French Alps9. Here, we use measurements from the Cloud–Aerosol Lidar with Orthogonal Polarization10, an air parcel trajectory model and a three-dimensional aerosol transport model to map the transport of dust clouds generated during a storm in China's Taklimakan Desert during May 2007. We show that the dust-veiled clouds were lofted to the upper troposphere around 8–10 km above the Earth's surface and transported more than one full circuit around the globe in about 13 days. When the dust reached the northwestern Pacific Ocean for the second time, the subsidence of a large-scale high-pressure system caused it to descend into the lower troposphere; some of the dust was then deposited over the ocean. Our analysis also indicates that the dust particles may have acted as ice nuclei in these high-altitude clouds, leading to the formation of cirrus clouds. We suggest that Asian dust can influence the global radiation budget by stimulating cirrus cloud formation and marine ecosystems by supplying nutrients to the open ocean.

Daytime and nighttime PM2.5 samples were collected at the summit of Mount Tai (1534 m) located in North China Plain during a week in 2006 summer. Size-segregated aerosol particles were also collected using an eight-stage impactor during the same period. Samples were analyzed for various water-soluble organic compounds using GC/FID and GC/MS techniques. Among the species identified in PM2.5 samples, dicarboxylic acids (C2–C11) were found as the most abundant compound class, followed by ketocarboxylic acids, saccharides, polyols and polyacids, and dicarbonyls. Daytime concentrations of most compounds were found to be 2–3 times higher than in nighttime. Such a diurnal variation was first interpreted by the depressed transport of pollutants in nighttime from the lowlands to the mountaintop owing to the decreased heights of planetary boundary layer, and second by the photochemical production in daytime. The diurnal variation trends of secondary organic aerosols (SOA) such as diacids at the mountain site are the same as those on lowlands, but the diurnal patterns of primary organic aerosols (POA) on the mountaintop are in contrast to those on lowlands, where POA such as saccharides and polyols are usually higher in nighttime owing to the accumulation within inversion layer developed. The eight-stage impactor samples showed bimodal distributions of diacids and related compounds peaking at size ranges of 0.70–1.1 μm and 5.8–9.0 μm. In the present study, water-soluble organics in the fine mode are largely originated from biomass burning and/or photooxidation of gaseous precursors and the subsequent adsorption on the preexisting particles, whereas those in the coarse mode are mainly derived from suspended soil particles and pollens and in part via the hygroscopic growth of fine particles and formation of cloud/fog droplets.

Char ac ter is tics of in di vid ual par ti cles from a super dust storm (DS) on 20 March 2002, and those of non dust storm

aero sols for Beijing (NDS) and Duolun (DL) (a desert area) are de ter mined us ing a va ri ety of meth ods. In China, typ i cally the

source of aero sols in dust storms is thought to be deserts with aluminosilicates be ing the main con stit u ent par ti cles; how ever,

this does not re flect a com plete anal y sis with our ev i dence in di cat ing po ten tial al ter nate dust sources along the storm’s trans port

path. In di vid ual par ti cle anal y sis of aero sols col lected from a super dust storm on 20 March 2002 in Beijing shows that among

all the 14 el e ments mea sured, only S and Cl have re mark able pos i tive cor re la tion. 82.5% of all par ti cles mea sured con tained

both S and Cl, and the rel a tive mass per cent age of S and Cl in these par ti cles is much higher than the av er age of all par ti cles.

62.0% of all par ti cles con tained S, Cl, and Na, in which the con cen tra tion of Na is 1.4 times higher than av er age. PMF (Pos i tive

Ma trix Factorization) anal y sis in di cates that NaCl and Na2SO4 are ma jor com po nents of these par ti cles with S and Cl show ing

sig nif i cant pos i tive cor re la tion. More over, SO4

2- and Cl- also show sig nif i cant pos i tive cor re la tion in bulk aero sol anal y sis.

XPS (X-ray Pho to elec tron Spec tros copy) anal y sis of the sur face of aero sols dem on strates that con cen tra tions of Na and S on

par ti cles from the dust storm are higher than those from non-dust storm par ti cles in Beijing and also for par ti cles from. It is very

likely that par ti cles en riched with S, Cl, and Na is from the sur face soils of dried salt-lakes and sa line soils en riched with

chlo ride and sul fate. This ev i dence dem on strates that be sides deserts, surface soils from dry salt-lakes and saline soils of arid

and semi-arid areas are also sources of particulates in dust storms over Beijing.

By using conventional micro-meteorological observation data of Beijing Yuetan Park Tower (180 m), the temperature profile of urban boundary layer (UBL), its characteristics and seasonal variation are analyzed. The main results are as follows: (1) In winter, the interdiurnal surface air temperature varia-tion at the surface is not synchronized with that of the upper levels, other than in summer and other seasons, which illuminates the impacts of Beijing’s geographical location, sky view factor and stably stratified nocturnal inversion. (2) Except that the stratification is unstable around noon, the stratifica-tion in the roof layer or above-roof layer is of seasonal variability, which is weak unstable or weak sta-ble in winter or summer respectively. This weak stable stratification possibly inhibits urban pollutant dispersion upwards in summer season. (3) The effect of urban building rooftop on the UBL thermal state has seasonal difference, that is, the rooftop plays the role of heating or cooling the urban roughness sublayer, in summer or winter respectively, which is similar to the effects of the Qing-hai-Tibet Plateau on the atmospheric thermal state.

By utilizing the air quality monitoring data and the NCEP reanalysis data, the relationship between the PM10 air pollution episode and synoptic situation is analyzed in the Beijing area. It is interesting to find that PM10 air pollution episode in and around the Beijing area is correlated with the Western Pacific tropical cyclone track to some extent, namely when a tropical cyclone lands southward to the Chang-jiang River, PM10 air pollution episode is not easy to take place generally in the Beijing area; but when a tropical cyclone moves northward and finally lands at the Korea Peninsula or the Japanese mainland, and under this condition the Beijing area is generally controlled by weak high or weak low for several days, PM10 air pollution episode often takes place in one day or several days. Above findings indicate that predicting the Western Pacific tropical cyclone track can foretell whether or not PM10 air pollution episode takes place in the Beijing area, which can offer a technique for urban air quality prediction and air pollution source management in the Beijing area.

Abstract：

According to the urbanization extent of Beijing area, and with 1980 as a turning point, the duration from 1961 to 2000 is divided into two periods: one is defined as the slow urbanization period from 1961 to 1980, and other one as the fast urbanization period from 1981 to 2000. Based on the 40-year’s precipi-tation data of 14 standard weather stations in Beijing area, the effect of urbanization on precipitation distribution is studied. It is found that there has been a noticeable and systematic change of winter precipitation distribution pattern between these two periods in Beijing area: in the slow urbanization period, the precipitation in the southern part of Beijing is more than that in the northern part; but in the fast urbanization period, the precipitation distribution pattern is reverse, i.e. the precipitation in the southern part is less than that in the northern part; But in other seasons, the precipitation distribution pattern did not change remarkably in general. The possible cause resulting in the change of winter precipitation distribution pattern, might be that with urban area extension, the effects of “urban heat island” and “urban dry island” become more and more intensified, and increase hydrometeors evapo-ration below precipitable cloud, and then cause less precipitation received on the ground surface in the downtown and the southern part. It is also noteworthy to further research why the precipitation distri-bution pattern does not change systematically in other seasons except winter after intense urbaniza-tion in Beijing area.

Keywords： urbanization urban precipitation urban heat island urban dry island Beijing area

In the period from June 2006 to December 2008, we measured the tropospheric nitrogen dioxide (NO2) column by ground-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) at an urban site in China (Tai’an) and three sites in Japan, covering urban (Yokosuka), suburban (Tsukuba), and remote areas (Hedo). This robust dataset is used to characterize Ozone Monitoring Instrument (OMI) tropospheric NO2 column data (the standard product, version 3). Correlations between MAX-DOAS and OMI data, both of which show very low NO2 at Hedo and moderate/high levels at the other sites, have correlation coefficients (R2) as high as 0.64, indicating that relative changes in OMI NO2 data are reliable. However, OMI data have a negative bias of 31% on average. Assuming that these results are valid for OMI data taken over China, we find an increasing trend in tropospheric column NO2 at about 5% per year on average in the industrial areas of China (30°-40°N and 110°-123°E) over 2005-2008, but its spatial distribution is highly inhomogeneous.

An observation-based box model approach was undertaken to estimate concentrations of OH, HO2, and RO2 radicals and the net photochemical production rate of ozone at the top of Mount Tai, located in the middle of Central East China, in June 2006. The model calculation was constrained by the measurements of O3, H2O, CO, NO, NO2, hydrocarbon, HCHO, and CH3CHO concentrations, and temperature and J values. The net production rate of ozone was estimated to be 6.4 ppb h−1 as a 6-h average (09:00–15:00 CST), suggesting 58 ppb of ozone is produced in one day. Thus the daytime buildup of ozone recorded at the mountain top as 23 ppb on average is likely affected by in situ photochemistry as well as by the upward transport of polluted air mass in the daytime. On days with high ozone concentrations (hourly values exceeding 100 ppb at least once), in situ photochemistry was more active than it was on low ozone days, suggesting that in situ photochemistry is an important factor controlling ozone concentrations. Sensitivity model runs for which different NOx and hydrocarbon concentrations were assumed suggested that the ozone production occurred normally under NOx-limited conditions, with some exceptional periods (under volatile-organic-compound-limited conditions) in which there was fresh pollution. We also examined the possible influence of the heterogeneous loss of gaseous HO2 radicals in contact with aerosol particle surfaces on the rate and regimes of ozone production.

Size-segregated (9 stages) n-alkanes, polycyclic aromatic hydrocarbons (PAHs) and hopanes in the urban (Baoji city in inland China), mountain (Mt. Tai in east coastal China) and marine (Okinawa Island, Japan) atmospheres over East Asia were studied using a GC/MS technique. Concentrations of n-alkanes (1698±568 ng m−3 in winter and 487±145 ng m−3 in spring), PAHs (536±80 and 161±39 ng m−3), and hopanes (65±24 and 20±2.4 ng m−3) in the urban air are 1–2 orders of magnitude higher than those in the mountain aerosols and 2–3 orders of magnitude higher than those in the marine samples. Mass ratios of n-alkanes, PAHs and hopanes clearly demonstrate coal-burning emissions as the major source of the determined organic aerosols. Size distributions of fossil fuel derived n-alkane, PAHs and hopanes were found as a unimodal in most cases, peaking at 0.7–1.1 μm size. In contrast, plant wax derived n-alkanes present a bimodal distribution with two peaks at the sizes of 0.7–1.1 μm and >4.7 μm in the summer mountain and spring marine samples. Among the three types of samples, geometric mean diameter (GMD) of the determined organics in fine mode (<2.1 μm) was the smallest (av. 0.63 μm in spring) in the urban samples and the largest (1.01 μm) in the marine samples, whereas the GMD in coarse mode (≥2.1 μm) was smallest (3.48 μm) in the marine aerosols and largest (4.04 μm) in the urban aerosols. The fine mode of GMDs in the urban and mountain samples were larger in winter than in spring and summer. Moreover, GMDs of 3- and 4-ring PAHs were larger than 5- and 6-ring PAHs in the three types of atmospheres. Such differences in GMDs may be interpreted by coagulation and repartitioning of organic compound during a long range transport from the inland continent to the marine site, suggesting that the size changes arising from these physical processes must be included in climate models in relevant to organic aerosols.

The measurement of volatile organic compounds (VOCs) was carried out at the summit of Mount Tai, located in the center of the Central East China (CEC) region, in June 2006 as part of the Mount Tai Experiment 2006 (MTX2006), which focused on the ozone and aerosol chemistry in the region. Temporal variations of simple VOCs between June 2 and June 28 revealed the characteristics of an aged air mass with minimum local influence. A comparison of VOCs observed at Mount Tai with other Chinese sites revealed relatively similar VOC levels to remote sites and, as expected, a lower level compared to more polluted sites. However, relatively high acetylene and benzene levels at Mount Tai were evidently indicated from comparison with normalized VOC profile by ethane suggested for Beijing. Owing to a shift in boundary layer height, we observed considerable differences between daytime and nighttime VOC concentrations. This suggests that the site has a very useful characteristic of being able to measure regional polluted air and the free troposphere regional background air quality. Influence of emissions from biomass burning in the region was evidently found to be extensive during the first half of the campaign (2–15 June), using fire spot data coupling with backward trajectory analysis. Agricultural residue burning was suggested as the primary source of emissions elucidated by the slope of the correlation plot between CH3Cl and CO obtained during the first half of the campaign.

To better understand the contribution of biogenic volatile organic compounds to the formation of secondary organic aerosol (SOA) in high mountain regions, ambient aerosols were collected at the summit of Mt. Tai (1534 m, a.s.l.), Central East China (CEC) during the Mount Tai eXperiment 2006 campaign (MTX2006) in early summer. Biogenic SOA tracers of isoprene, monoterpenes, and β-caryophyllene oxidation products were measured using gas chromatography/mass spectrometry. All the biogenic SOA tracers showed no clear diurnal variations, suggesting that they are formed during long-range atmospheric transport. Although isoprene- and monoterpene-derived SOA tracers did not correlate with levoglucosan (a biomass burning tracer), β-caryophyllinic acid showed a good correlation with levoglucosan, indicating that biomass burning may be a source for this compound. Total concentrations of isoprene oxidation products are much higher than those of monoterpene and β-caryophyllene oxidation products. The ratio of isoprene to monoterpene oxidation products (Riso/mono) was found to co-vary with ozone and NOx during the summer campaign. The average Riso/mono value was 6.94 at daytime and 10.0 at nighttime. These values are among the highest in the aerosols studied in different regions, which may be due to the large isoprene fluxes, high O3 and NOx levels and relatively high OH concentrations in CEC. Using a tracer-based method, we estimated the average concentrations of secondary organic carbon (SOC) derived from isoprene, monoterpenes, and β-caryophyllene to be 1.76 μgC m−3 at daytime and 1.85 μgC m−3 at nighttime. These values correspond to 11.2% and 11.0% of the total OC concentrations, in which isoprene-derived SOC are 7.4% and 8.0% at day- and night-time, respectively. This study suggests that isoprene is a more significant precursor for biogenic SOA than monoterpenes and β-caryophyllene in high altitude in CEC.

The ensemble Kalman filter (EnKF), as a unified approach to both data assimilation and ensemble forecasting problems, is used to investigate the performance of dust storm ensemble forecasting targeting a dust episode in the East Asia during 23--30 May 2007. The errors in the input wind field, dust emission intensity, and dry deposition velocity are among important model uncertainties and are considered in the model error perturbations. These model errors are not assumed to have zero-means. The model error means representing the model bias are estimated as part of the data assimilation process. Observations from a LIDAR network are assimilated to generate the initial ensembles and correct the model biases. The ensemble forecast skills are evaluated against the observations and a benchmark/control forecast, which is a simple model run without assimilation of any observations. Another ensemble forecast experiment is also performed without the model bias correction in order to examine the impact of the bias correction. Results show that the ensemble-mean, as deterministic forecasts have substantial improvement over the control forecasts and correctly captures the major dust arrival and cessation timing at each observation site. However, the forecast skill decreases as the forecast lead time increases. Bias correction further improved the forecasts in down wind areas. The forecasts within 24 hours are most improved and better than those without the bias correction. The examination of the ensemble forecast skills using the Brier scores and the relative operating characteristic curves and areas indicates that the ensemble forecasting system has useful forecast skills.

The impact of open crop residual burning on O3, CO, Black Carbons (BC), and Organic Carbons (OC) concentrations over Central Eastern China (CEC) during the Mount Tai Experiment 2006 (MTX2006) was evaluated using the regional chemical transport model, the Models-3 Community Multiscale Air Quality Modeling System (CMAQ). To investigate these pollutants during the MTX2006 period in June, daily gridded emissions from open crop residual burning were developed based on a bottom-up methodology and using land cover and hotspot information from satellites. This model system which involves daily emissions from open biomass burning, captured monthly-averaged observed concentrations and day-to-day variations in the patterns of O3, CO, BC, and OC with good correlation coefficients between models and observations, ranging from 0.54 to 0.66. These results were significantly improved from those using annual emissions. For monthly-averaged O3, the simulated concentration of 81.5 ppbv was close to the observed concentration (82.5 ppbv). The period of MTX2006 was roughly divided into two parts: 1) polluted days with heavy open crop residual burning in the first half of June; 2) cleaner days with negligible field burning in the latter half of June. Additionally, the first half of June was defined by two high pollution episodes during 5–7 and 12–13 June, and a relatively cleaner episode during 8–10 June between these two high pollution episodes. In the first polluted episode, this model captured high O3, CO, BC, and OC concentrations at the summit of Mount Tai which were affected by open crop residual burning in the south of CEC and northward transport. For this episode, the impacts from open crop residual burning were 12% for O3, 35% for CO, 56% for BC, and 80% for OC over CEC. The daily emissions from open crop residual burning were an essential factor to evaluate the pollutants during the MTX2006. These emissions have a large impact not only on primary pollutants but also on secondly pollutions, such as O3, in the first half of June over northeastern Asia. On the other hand, this model did not capture the second polluted episode and underestimated observed CO and BC. Improvements of both anthropogenic and open burning emissions and CO inflow from model boundary are necessary to improve both anthropogenic and open burning emissions and CO inflow to evaluate the pollutants using this model.

Owing to recent industrialization, Central East China has become a significant source of air pollutants. To examine the processes controlling the chemistry and transport of tropospheric ozone, we continuously measured non-methane volatile organic compounds (NMVOCs) as part of an intensive field campaign at Mount Tai, China, in June 2006 (MTX2006), using proton transfer reaction mass spectrometry (PTR-MS). Temporal variations of NMVOCs were recorded in mass-scan mode from m/z 17 to m/z 300 during 12–30 June 2006. More than thirty kinds of NMVOCs were detected up to m/z 160, including alkenes, aromatics, alcohols, aldehydes, and ketones. Oxygenated VOCs were the predominant NMVOCs. During the night of 12 June, we observed an episode of high NMVOCs concentrations attributed to the burning of agricultural biomass. The ΔNMVOCs/ΔCO ratios derived by PTR-MS measurements for this episode are compared to emission ratios from various types of biomass burning as reviewed by Andreae and Merlet (2001) and to ratios recently measured by PTR-MS in tropical forests (Karl et al., 2007) and at urban sites (Warneke et al., 2007).

Connections between the spring Antarctic Oscillation (AAO) and the East Asian summer monsoon

(EASM) in two reanalysis datasets—NCEP-1 (NCEP/NCAR Reanalysis 1) and ERA-40 (ECMWF 40-

year Reanalysis)—are investigated in this study. Both show significant correlation between AAO and EASM

rainfall over the Yangtze River valley, especially after about 1985. Though ERA-40 shows weaker anomalous

signals connecting AAO and EASM over southern high latitudes than NCEP-1, both datasets reveal similar

connecting patterns between them. A wave-train-like pattern appears in the upper levels, from southern high

latitudes through east of Australia and from the Maritime Continent to East Asia. In positive AAO years,

the cross equatorial southeasterly flow over the Maritime Continent in the lower levels is strengthened, the

specific humidity of the whole atmosphere over East Asia increases, and convective activity is enhanced; thus

the summer rainfall over East Asia increases. The spring AAO-EASM connection may be better represented

in ERA-40.

The author investigates the prediction of

Northeast China’s winter surface air temperature (SAT),

and first forecast the year to year increment in the predictand

and then predict the predictand. Thus, in the first step,

we determined the predictors for an increment in winter

SAT by analyzing the atmospheric variability associated

with an increment in winter SAT. Then, multi-linear regression

was applied to establish a prediction model for

an increment in winter SAT in Northeast China. The prediction

model shows a high correlation coefficient (0.73)

between the simulated and observed annual increments in

winter SAT in Northeast China throughout the period

1965−2002, with a relative root mean square error of

−7.9%. The prediction model makes a reasonable hindcast

for 2003−08, with an average relative root mean square

error of −7.2%. The prediction model can capture the increasing

trend of winter SAT in Northeast China from

1965−2008. The results suggest that this approach to

forecasting an annual increment in winter SAT in Northeast

China would be relevant in operational seasonal

forecasts.

To examine the zonal asymmetry of the Antarctic

oscillation (AAO), different portions of the AAO

from June to October (JJASO) in the interannual variability

of the Atlantic tropical hurricanes number (ATHN) are

documented in this research. It follows that the AAO in

the Western Hemisphere (AAOWH) is positively correlated

with the ATHN, at 0.36 during the period of

1871−1998 and 0.42 during the period of 1949−98. After

removing the linear regressions on the Southern Oscillation

Index (SOI) in all time series, the above correlation

coefficients are 0.25 and 0.30, respectively. The underlying

mechanisms are studied through analyses of the atmospheric

general circulation variability associated with

the AAOWH. It turns out that the positive (negative)

phase of JJASO AAOWH corresponds with several factors:

decreased (increased) vertical zonal wind shear

magnitude, low-level anomalous convergence (divergence),

high-level anomalous divergence (convergence),

and warmed (cooled) sea surface temperature in the

tropical Atlantic. Therefore, the positive (negative) phase

of JJASO AAOWH is favorable (unfavorable) to the

tropical hurricane genesis.

A new approach to forecasting the year-to-year increment of rainfall in North China in July-August (JA) is proposed. DY is defined as the difference of a variable between the current year and the preceding year (year-to-year increment). NR denotes the seasonal mean precipitation rate over North China in JA. After analyzing the atmospheric circulation anomalies associated with the DY of NR, five key predictors for the DY of NR have been identified. The prediction model for the DY of NR is established by using multi-linear regression method and the NR is obtained (the current forecasted DY of NR added to the preceding observed NR). The prediction model shows a high correlation coefficient (0.8) between the simulated and the observed DY of NR throughout period 1965－1999, with an average relative root mean square error of 19% for the percentage of precipitation rate anomaly over North China. The prediction model makes a hindcast for 2000－2007, with an average relative root mean square error of 21% for the percentage of precipitation rate anomaly over North China. The model reproduces the downward trend of the percentage of precipitation rate anomaly over North China during 1965－2006. Because the current operational prediction models of the summer precipitation have average forecast scores of 60%－70%, it has been more difficult to forecast the summer rainfall over North China. Thus this new approach for predicting the year-to-year increment of the summer precipitation (and hence the summer precipitation itself) has the potential to significantly improve operational forecasting skill for summer precipitation.

The year-to-year increment prediction approach

proposed by was applied to forecast the annual

number of tropical cyclones (TCs) making landfall over

China. The year-to-year increase or decrease in the number

of land-falling TCs (LTCs) was first predicted to yield

a net number of LTCs between successive years. The statistical

prediction scheme for the year-to-year increment

of annual LTCs was developed based on data collected

from 1977 to 2007, which includes five predictors associated

with high latitude circulations in both Hemispheres

and the circulation over the local, tropical western North

Pacific Ocean. The model shows reasonably high predictive

ability, with an average root mean square error

(RMSE) of 1.09, a mean absolute error (MAE) of 0.9, and

a correlation coefficient between the predicted and observed

annual number of LTCs of 0.86, accounting for

74% of the total variance. The cross-validation test further

demonstrated the high predictive ability of the model,

with an RMSE value of 1.4, an MAE value of 1.2, and a

correlation coefficient of 0.74 during this period.

The spatial and temporal distributions of the anthropogenic radionuclides 137Cs and 90Sr, originating

from nuclear bomb testing, the Sellafield reprocessing plant in the Irish Sea (UK), and from the Ob and

Yenisey river discharges to the Arctic Ocean, have been simulated using the global version of the Miami

Isopycnic Coordinate Ocean Model (MICOM). The physical model is forced with daily atmospheric

re-analysis fields for the period of 1948–1999. Comparison of the temporal evolution of the observed and

the simulated concentrations of 90Sr has been performed in the Kara Sea. The relative contributions of

the different sources on the temporal and spatial distributions of the surface 90Sr are quantified over the

simulated period. It follows that the Ob river discharge dominated the surface 90Sr over most of the Arctic

Ocean and along the eastern and western coasts of Greenland before 1960. During the period of 1980–

1990, the atmospheric fallout and the Ob river discharge were equally important for the 90Sr distribution

in the Arctic Ocean. Furthermore, an attempt has been made to explore the possible dispersion of

accidental released 90Sr from the Ob and Yenisey rivers under a global warming scenario (2  CO2). The

difference between the present-day and the global warming scenario runs indicates that more of the

released 90Sr from the Ob and Yenisey rivers is confined to the Arctic Ocean in the global warming run,

particularly in the near coastal, non-European part of the Arctic Ocean.

The relationship between the North Asia cyclone (NAC) activity and the Southern Annular Mode (SAM) is documented in this research. The definition of the NAC index (NACI) is based on the atmospheric relative vorticity in North Asia. The analysis yields a significant positive correlation between previous winter Southern Annular Mode index (SAMI) and spring NACI in the interannual variability, with a correlation coefficient of 0.51 during 1948-2000. Analysis of the NAC-related and SAM-related atmospheric general circulation variability demonstrates such a relationship. The study further reveals that when the winter SAM becomes strong, the springtime atmospheric convection in tropical western Pacific will intensify and the local Hadley circulation will be strengthened. As a result, the abnormal subsiding motion over South China makes the temperature gradient intensified in the low level and strengthens the jet in the high level, both of which are beneficial to the development of NAC activity.

The Subpolar Gyre index (SPG), derived from the analysis of sea surface height (SSH), is proposed to be a potential indicator for the North Atlantic Meridional Overturning Circulation (AMOC) based on observation as well as the Ocean General Circulation Model (OGCM). We investigated the correspondence between the SPG and the AMOC in a coupled climate model. Our results con-firm that the SPG can be used as an early indicator for the AMOC in the subtropical North Atlantic. Changes in the SPG are closely related to variations in the air-sea heat exchange in the Labrador Sea, and variations in deep wa-ter formation and southward dense water transport are closely related to the deep western boundary current (DWBC) in the North Atlantic.

The effects of ocean density vertical stratification and related ocean mixing on the transient response of the Atlantic Meridional Overturning Circulation (AMOC) are examined in a freshwater perturbation simulation using the Bergen Climate Model (BCM). The results presented here are based on the model outputs of previous freshwater experiment: a 300-year control integration (CTRL), a freshwater integration (FW1) which started after 100 years running of CTRL, with an artificially and continuously threefold increase in the freshwater flux to the Greenland-Iceland-Norwegian (GIN) Seas and the Arctic Ocean throughout the following 150-year simulation. In FW1, the transient response of the AMOC exhibits an initial decreasing of about 6 Sv (1 Sv = 106 m3 s-1) over the first 50-year integration and followed a gradual recovery during the last 100-year integration. Our results show that the vertical density stratification as the crucial property of the interior ocean plays an important role for the transient responses of AMOC by regulating the convective and diapycnal mixings under the enhanced freshwater input to northern high latitudes in BCM in which the ocean diapycnal mixing is stratification-dependent. The regulating mechanism can be generalized as follows: during the initial freshwater integrations, the vertical density stratification in ocean upper layers of northern high latitudes is more stabilized with the enhanced freshwater input, leading to the reduced wintertime convective mixing in North Atlantic (NA) and thereafter the reduced North Atlantic Dense Water (NADW) formation and finally to a weakened AMOC. On the other hand, the decreased southward returning of the NADW weakens the vertical density stratification in the intermediate and deep ocean at the low-and mid-latitudes, resulting in the basin-scale upwelling of the deep dense water increased. Such response contributes to the recovery of volume and salt transport to the high northern Atlantic and counteracts to the freshening in sub-polar regions, leading to the recovery of Sea Surface Salinity (SSS) there. Consequently, the initial stabilized vertical density stratification of ocean upper layer tends to be unstable in winter, giving rise to the recoveries of NADW formation and AMOC during the last 100-year integration in FW1.

Based on NCEP/NCAR reanalysis data, the interdecadal variability of Hadley circulation (HC) and its association with East Asian temperature in winter are investigated. Results indicate that the Northern

Hemisphere winter HC underwent apparent change in the 1970s, with transition occurring around 1976/77.

Along with interdecadal variability of HC, its linkage to surface air temperature (SAT) in East Asia also varied decadally, from weak relations to strong relations. Such a change may be related to the interaction between HC and the atmospheric circulation system over the Philippines, which is associated with the East Asian winter monsoon (EAWM). Before the 1970s, the connection between HC and the anticyclonic circulation around the Philippines was insigni¯cant, but after the late 1970s their linkage entered a strong regime. The intensi¯cation of this connection may therefore be responsible for the strong relations between

HC and East Asian winter temperatures after the late 1970s.

On the occasion of celebrating the 80th anniversary (1928-2008) of the Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences, the authors very briefly reviewed some new result s in the research of the interannual climate variability and short-term climate prediction in recent years, most in the past five years. Some of the studies were jointly completed by the scientists from both the IAP and other institutions. The review was categorized into three parts, the interannual climate variability, ENSO prediction, and the numerical climate prediction.

Fan (2007) recently documented the zonal asymmetry of the Antarctic oscillation (AAO) in the austral winter. In this research, the zonal asymmetry of the northern annular mode, or the Arctic oscillation (AO), in the interannual variability is studied for the boreal winter. It is shown that there is zonal

asymmetry of the AO as well, similar to the case of the Antarctic oscillation (AAO). However, the zonal asymmetry of the AO is considerably weaker than that of the AAO. This is far beyond the speculation, since the zonal asymmetry of the geography is larger in the Northern Hemisphere than the Southern Hemisphere. The Western and Eastern Hemispheres ortions of the AO are correlated at 0.54 for 1959-1998, comparing with 0.23 for the case of the AAO. The authors also discussed the physical reason for

this inter-hemispheric difference, and partly attributed it to the El Niño and Southern Oscillation (ENSO) cycle which may be represented by the SO index. It is indicated that the SO associated sea-level

pressure (SLP) patterns are more zonal symmetric in the high latitudes of the Northern Hemisphere than the Southern Hemisphere.

Using correlation and EOF analyses on sea level pressure from 57-year NCEP-NCAR reanalysis data, the Arabian Peninsula-North Pacific Oscillation (APNPO) is identified. The APNPO reflects the

co-variability between the North Pacific high and South Asian summer monsoon low. This teleconnection pattern is closely related to the Asian summer monsoon. On interannual timescale, it co-varies with

both the East Asian summer monsoon (EASM) and South Asian summer monsoon (SASM); on decadal timescale, it co-varies with the EASM: both exhibit two abrupt climate changes in the middle 1960s and the late 1970s respectively. The possible physical process for the connections between the APNPO and Asian summer monsoon is then explored by analyzing the APNPO-related atmospheric circulations. The results show that with a strong APNPO, the Somali Jet, SASM flow, EASM flow, and South Asian

high are all enhanced, and an anomalous anticyclone is produced at the upper level over northeast China via a zonal wave train. Meanwhile, the moisture transportation to the Asian monsoon regions is also strengthened in a strong APNPO year, leading to a strong moisture convergence over India and northern China. All these changes of circulations and moisture conditions finally result in an anomalous Asian summer monsoon and monsoon rainfall over India and northern China. In addition, the APNPO has a good persistence from spring to summer. The spring APNPO is also significantly orrelated with Asian summer monsoon variability. The spring APNPO might herefore provide valuable information

for the prediction of Asian summer monsoon.

The relationship between the summer (July–September) North Atlantic Oscillation

(SNAO) and simultaneous East Asian air temperature is investigated. The results show that the SNAO is related to middle East Asian summer air temperature, however this linkage varies with time on decadal timescale: a strong connection appears after the late 1970s but a weak connection before the late 1970s. Further analysis indicates that this instable relationship may have resulted from the shift of the SNAO mode around the late

1970s. In the period of 1979–2003, the centers of the SNAO mode are located more

eastward. A positive-phase (negative-phase) SNAO produces a strong lower-level

divergence (convergence) over the Asian jet entrance region, in turn stimulates a strong upper-level convergence divergence) via the Ekman pumping. Such a convergence (divergence) then excites a zonally oriented quasi-stationary barotropical Rossby wave train along the Asian upper-level jet. Thus the SNAO ignal is transported eastward to East Asia, resulting in an anomalous summer air temperature over middle East Asia.

However, in the period of 1951–1975, the centers of the SNAO mode are located more

westward. The associated upper-level divergence/convergence is away from the Asian jet entrance region, and the SNAO signal cannot be transported eastward to East Asia. Hence the connection is broken.

A basin-scale warming is the leading mode of tropical Indian Ocean sea surface temperature (SST) variability on interannual time scales, and it is also the prominent feature of the interdecadal SST trend in recent decades. The influence of the warming on the East Asian summer monsoon (EASM) is investigated through ensemble experiments of several atmospheric general circulation models (AGCMs). The results from five AGCMs consistently suggest that near the surface, the Indian Ocean warming forces an anticyclonic anomaly over the subtropical western Pacific, intensifying the southwesterly winds to East China; and in the upper troposphere, it forces a Gill-type response with the intensified South Asian high, both favoring the enhancement of the EASM. These processes are argued to contribute to the stronger EASM during the summer following the peak of El Nino than monsoons in other years. These model results also suggest that tropical Indian Ocean warming may not have a causal relationship to the synchronous weakening of EASM on interdecadal time scales.

Ensemble experiments with an atmospheric general circulation model reveal that a positive (warm) ocean phase of the Atlantic Multidecadal Oscillation (AMO) increases Indian summer rainfall. The intensification is driven by extratropical North Atlantic warmth, with some cancellation associated with monsoon weakening in response to tropical North Atlantic warmth. Mechanistically, warm extratropical North Atlantic SSTs increase local rainfall, inducing an arching extratropical wavetrain response. The latter leads to intensified northern subsidence of monsoon mean meridional streamflow as well as widespread low surface pressure over North Africa, the Middle East and the western Indian Ocean contributing to a strengthened Indian monsoon trough and increased monsoon rainfall. Warm tropical North Atlantic SSTs primarily increase local tropical Atlantic rainfall that induces a tropically-confined response consisting of low level easterly wind anomalies over the Indian Ocean and dynamically induced subsident drying over India.

Somali Jet changes will influence the variability of Asian monsoon and climate.How would Somali Jet changes respond to the global warming in the future climate? To address this question,we first evaluate the ability of IPCC-AR4 climate models and perform the 20th century climate in coupled models (20C3M) experiments to reproduce the observational features of the low level Somali Jet in JJA (June-July-August) for the period 1976-1999.Then,we project and discuss the changes of Somali Jet under the climate change of Scenario A2 (SRESA2) for the period 2005-2099. The results show that 18 IPCC-AR4 models have performed better in describing the climatological features of Somali Jet in the present climate simulations. Analysis of Somali Jet intensity changes from the multi-model ensemble results for the period 2005-2099 shows a weakened Somali Jet in the early 21st century (2010-2040), the strongest Somali Jet in the middle 21st century (2050-2060), as well as the weakest Somali Jet at the end of the 21st century (2070-2090). Compared with the period 1976-1999, the intensity of Somali Jet is weakening in general, and it becomes the weakest in the end of the 21st century. The results also suggest that the relationship between the intensity of Somali Jet in JJA and the increment of global mean surface air temperature is nonlinear, which is reflected differently among the models, suggesting the uncertainty of the IPCC-AR4 models. Considering the important role of Somali Jet in the Indian monsoon and East Asian monsoon and climate of China, the variability of Somali Jet and its evolvement under the present climate or future climate changes need to be further clarifed.

In 2006, China’s carbon dioxide emission rate reached 1.6 GtC (gigatons of carbon or 1015 g carbon) per year (see chart, below) (1–3). Economic growth is projected to continue at higher than 7% per year; at this rate, Gross Domestic Product (GDP) would quadruple in 20 years. The associated high CO2 emission rate would substantially affect the goal of avoiding dangerous climate change as set by the United Nations Framework Convention on Climate Change (UNFCCC). The conflict between economic development and keeping atmospheric greenhouse gases at a manageable level poses one of the greatest challenges of this century.

Formaldehyde (HCHO), the most abundant carbonyl compound in the atmosphere, is generated as an intermediate product in the oxidation of nonmethane hydrocarbons. Proton transfer reaction mass spectrometry (PTR-MS) has the capability to detect HCHO from ion signals at m/z 31 with high time-resolution. However, the detection sensitivity

is low compared to other detectable species, and is considerably affected by humidity, due to back reactions between protonated HCHO and water vapor prior to analysis. We performed a laboratory calibration of PTR-MS for HCHO and examined the detection sensitivity and humidity dependence

at various field strengths. Subsequently, we deployed

the PTR-MS instrument in a field campaign at Mount Tai in China in June 2006 to measure HCHO in various meteorological and photochemical conditions; we also conducted intercomparison measurements by Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS). Correction of interference in the m/z 31 signals by fragments from proton transfer reactions with methyl hydroperoxide, methanol, and ethanol greatly improves agreement between the two methods,

giving the correlation [HCHO]MAX−DOAS=(0.99±0.16)

[HCHO]PTR−MS+(0.02±0.38), where error limits represent 95% confidence levels.

A detailed systematic aerosol source apportionment study was performed with two intensive sampling campaigns in the spring dust storm seasons of 2001 and 2002 in Beijing, China. The concentrations of 23 elements and 15 ions and the total mass in 115 total suspended particulate (TSP) samples were measured. Combining enrichment factors, elemental signatures, back trajectory analysis, bilinear positive matrix factorization (PMF2) analysis with the meteorological pattern, the mixing of mineral aerosol with pollution aerosol and their apportionments in different dust episodes were elucidated. Ca/Al was proved to be a good signature to trace different dust origin areas. Soil dust, road dust, secondary, industrial/coal combustion, salts, phosphates, nitrites, and oil combustion were identified by PMF to be the eight main sources. Soil dust (from outside) increased sharply when cold front intruded Beijing in dust events (80–95% of total dust), which neutralized local acidic aerosol. Road dust (from local by re-suspension) contributed 15–30% of the total TSP. Intruded dusts brought lots of sulfate (from soil containing high-S or from pollutants introduced on the pathway) but little nitrate. The secondary sulfate/nitrate and the total pollutants contributed 25% and 40–50%, respectively, of the TSP in those dust episodes, which were transported in lower layer and mixed strongly with local re-suspended pollution aerosols. Sulfur/Nitrogen oxidation ratios in dust storms and in non-dust storms were <2% and 10–40%, respectively, and had a little jumps just after dust peaks, which indicated that dust provided a good basic surface for the heterogeneous reactions.

This paper focuses on the comparison of chemical deposition of eight regional chemical models used in Model Inter-Comparison Study for Asia (MICS-Asia) II. Monthly-mean depositions of chemical species simulated by these models, including dry deposition of SO2, HNO3, NH3, sulfate, nitrate and ammonium and wet deposition of SO42−, NO3− and NH4+, have been provided for four periods (March, July, December 2001 and March 2002) in this work. Observations at 37 sites of the Acid Deposition Monitoring Network in East Asia (EANET) are compared with SO42−, NO3− and NH4+ wet deposition model results. Significant correlations appeared between the observation and computed ensemble mean of participant models. Also, differences among modeled sulfur and nitrogen dry depositions have been studied at the EANET sites. Based on the analysis of acid deposition for various species from different models, total depositions of sulfur (SO2 and sulfate) and nitrogen (nitrate and ammonium) have been evaluated as the ensemble mean of the eight models. In general, all models capture the observed spatial distribution of sulfur and nitrogen deposition, although the absolute values may differ from measurements. High deposition often occurs in eastern China, Japan, the Republic of Korea, Thailand, Vietnam, Philippines and other parts of Southeast Asia. The magnitude of model bias is quite large for many of the models. In examining the reasons for model–measurement disagreement, we find that differences in chemical processes, deposition parameterization, and modeled precipitation are the main reasons for large model disparities.

We present detailed 3D structure of Asian dust outflow

from a dust source region to the northwestern Pacific ocean

retrieved by NASA/CALIOP onboard CALIPSO and results

simulated by a four-dimensional variational (4DVAR) data

assimilation version of a dust transport model (RC4) based

on the NIES Lidar network. The modeled and CALIOP dust

extinction showed good agreement, both for horizontal

scale (600–1200 km) and vertical depth (1600–3600 m)

near the dust source regions. Cross-section analyses of

CALIOP and RC4 assisted by forward trajectory revealed

that dust from the Gobi Desert on 5 May traveled

approximately 1000–1500 km/day to the east and passed

over Japan on 8 May. The elevated dust subsequently

passed to the Pacific Ocean while maintaining the major

dust layer height of 2500–4000 m MSL trapped within the

potential temperature of 302–306 K. Results of our

analyses demonstrate the importance of integration of

CALIOP measurement and the dust model for clarifying

the overall structure of an Asian dust event.

Aerosol nucleation events have been observed at a variety of locations worldwide, and may have significant climatic and health implications. While ions have long been suggested as favorable nucleation embryos, their significance as a global source of particles has remained uncertain. Here, an ion-mediated nucleation (IMN) mechanism, which incorporates new thermodynamic data and physical algorithms, has been integrated into a global chemical transport model (GEOS-Chem) to study ion-mediated particle formation in the global troposphere. The simulated annual mean results have been compared to a comprehensive set of data relevant to particle nucleation around the globe. We show that predicted annual spatial patterns of particle formation agree reasonably well with land-, ship-, and aircraft-based observations. Our simulations show that, globally, IMN in the boundary layer is largely confined to two broad latitude belts: one in the northern hemisphere (~20° N–70° N), and one in the southern hemisphere (~30° S–90° S). In the middle latitude boundary layer over continents, the annual mean IMN rates are generally above 104 cm−3day−1, with some hot spots reaching 105 cm−3day−1. The zonally-averaged vertical distribution of IMN rates indicates that IMN is significant in the tropical upper troposphere, the entire middle latitude troposphere, and over Antarctica. Comparing the relative strengths of particle sources due to IMN and due to primary particle emissions demonstrates that IMN is significant on a global scale. Further research is needed to reduce modeling uncertainties and to understand the ultimate contribution of freshly nucleated particles to the abundance of cloud condensation nuclei.

Eight regional Eulerian chemical transport models (CTMs) are compared with each other and with an extensive set of observations including ground-level concentrations from EANET, ozone soundings from JMA and vertical profiles from the TRACE-P experiment to evaluate the models’ abilities in simulating O3 and relevant species (SO2, NO, NO2, HNO3 and PAN) in the troposphere of East Asia and to look for similarities and differences among model performances. Statistical analysis is conducted to help estimate the consistency and discrepancy between model simulation and observation in terms of various species, seasons, locations, as well as altitude ranges. In general, all models show a good skill of simulating SO2 for both ground level and the lower troposphere, although two of the eight models systematically overpredict SO2 concentration. The model skills for O3 vary largely with region and season. For ground-level O3, model results are best correlated with observations in July 2001. Comparing with O3 soundings measured in the afternoon reveals the best consistency among models in March 2001 and the largest disparity in O3 magnitude in July 2001, although most models produce the best correlation in July as well. In terms of the statistics for the four flights of TRACE-P experiment, most models appear to be able to accurately capture the variability in the lower troposphere. The model performances for NOx are relatively poor, with lower correlation and with almost all models tending to underpredict NOx levels, due to larger uncertainties in either emission estimates or complex chemical mechanism represented. All models exhibit larger RMSE at altitudes o2 km than 2–5.5 km, mainly due to a consistent tendency of these models towards underprediction of the magnitude of intense plumes that often originate from near surface. Relatively lower correlation at altitudes 2–5.5km may be attributed to the models’ limitation in representing convection or potential chemical processes. Most of the key features in species distribution have been consistently reproduced by the participating models, such as the O3 enhancement in the western Pacific Ocean in March and in northeast Asia in July, respectively, although the absolute model values may differ considerably from each other. Large differences are found among models in the southern parts of the domain for all the four periods, including southern China and northern parts of some Southeast Asia countries where the behaviors of chemical components and the ability of these models are still not clearly known because of a lack of observational databases.

Keywords: Chemical transport model; EANET; TRACE-P; Evaluation; Model intercomparison; O3 and relevant species; Seasonality

An Ensemble Kalman Filter (EnKF) data assimilation system was developed for a regional dust transport model. This paper applied the EnKF method to investigate modeling of severe dust storm episodes occurring in March 2002 over China based on surface observations of dust concentrations to explore the impact of the EnKF data assimilation systems on forecast improvement. A series of sensitivity experiments using our system demonstrates the ability of the advanced EnKF assimilation method using surface observed PM10 in North China to correct initial conditions, which leads to improved forecasts of dust storms. However, large errors in the forecast may arise from model errors (uncertainties in meteorological fields, dust emissions, dry deposition velocity, etc.). This result illustrates that the EnKF requires identification and correction model errors during the assimilation procedure in order to significantly improve forecasts. Results also show that the EnKF should use a large inflation parameter to obtain better model performance and forecast potential. Furthermore, the ensemble perturbations generated at the initial time should include enough ensemble spreads to represent the background error after several assimilation cycles.

Results from the Model Intercomparison Study Asia Phase II (MICS-Asia II) are presented. Nine different regional modeling groups simulated chemistry and transport of ozone (O3), secondary aerosol, acid deposition, and associated precursors, using common emissions and boundary conditions derived from a global model. Four-month-long periods, representing 2 years and three seasons (i.e., March, July, and December in 2001, and March in 2002), are analyzed. New observational data, obtained under the EANET (the Acid Deposition Monitoring Network in East Asia) monitoring program, were made available for this study, and these data provide a regional database to compare with model simulations. The analysis focused around seven subject areas: O3 and related precursors, aerosols, acid deposition, global inflow of pollutants and precursor to Asia, model sensitivities to aerosol parameterization, analysis of emission fields, and detailed analyses of individual models, each of which is presented in a companion paper in this issue of Atmospheric Environment. This overview discusses the major findings of the study, as well as information on common emissions, meteorological conditions, and observations.

Keywords: Air quality modeling; Asia air quality; Ozone; Aerosol composition

Eight chemical transport models participate in a model intercomparison study for East Asia, MICS-Asia II. This paper analyzes calculated results for particulate matter of sulfate, nitrate and ammonium through comparisons with each other and with monthly measurements at EANET (the acid deposition monitoring network in East Asia) and daily measurements at Fukue, Japan. To the EANET measurements, model ensemble means better agree with model individual results for sulfate and total ammonium, although total nitrate is consistently and considerably underestimated. To measurements at Fukue, the models show better agreement than for the EANET measurements. This is likely because Fukue is centered in many of the model domains, whereas the EANET stations are mostly in Southeast Asia and Russia. Moreover, it would be important that Fukue is in Northeast Asia, where the emission inventory is more reliable than Southeast Asia. The model–model comparisons are made in view of the total amount in the atmosphere, vertical profile, coefficient of variation in surface concentrations, and transformation changes with distance. All the models show reasonable tendencies

in vertical profiles and composition ratios. However, total amounts in the atmosphere are discrepant among the models. The consistency of the total amount in the atmosphere would influence source–receptor analysis. It seems that model results would be consistent, if the models take into account the primitive processes like emission, advection/diffusion, chemical transformation and dry/wet deposition, no matter the processes are modeled simply or comprehensively.

Through the comparison study, we learned that it would be difficult to find any problems from one comparison (model observation comparison with one data or many but at one station or in a short period). Modelers tend to examine model performances only from model-observation comparisons. However, taking budget in a certain or whole model domain would be important, before the models are applied to source–receptor analysis.

Keywords: Chemical transport models; Model intercomparison; EANET; Sulfate; Nitrate

This study quantifies the seasonality and geographic variability of global pollutant inflow to Asia. Asia is often looked to as a major source of intercontinental air pollution transport with rising emissions and efficient pollutant export processes. However, the degree to which foreign emissions have been imported to Asia has not been thoroughly examined. The Model Inter-Comparison Study for Asia (MICS-Asia) is an international collaboration to study air pollution transport and chemistry in Asia. Using the global atmospheric chemistry Model of Ozone and Related Tracers (MOZART v. 2.4), and comparing results with a suite of regional models participating in MICS-Asia, we find that imported O3 contributes significantly throughout Asia. The choice of upper boundary condition is found to be particularly important for O3, even for surface concentrations. Both North America and Europe contribute to ground-level O3 concentrations throughout the region, though the seasonality of these two sources varies. North American contributions peak at over 10% of monthly mean O3 during winter months in East Asia, compared to Europe’s spring- and autumn-maxima (5–8%). In comparison to observed data from the Acid Deposition Monitoring Network in East Asia (EANET), MOZART concentrations for O3 generally fall within the range of the MICS models, but MOZART is unable to capture the fine spatial variability of shorter-lived species as well as the regional models.

Keywords: MICS-Asia; Inter-comparison; Hemispheric transport; Air pollution; Ozone; Carbon monoxide

Mass concentrations of black carbon (BC) were determined in June 2006 at the top of Mount Tai (36.26° N, 117.11° E, 1534 m a.s.l.), located in the middle of Central East China, using four different instruments: a multi-angle absorption photometer (5012 MAAP, Thermo), a particle soot absorption photometer (PSAP, Radiance Research), an ECOC semi-continuous analyzer (Sunset Laboratory) and an Aethalometer (AE-21, Magee Scientific). High correlation coefficients (R2>0.88) were obtained between the measurements of the BC mass concentrations made using the different instruments. From the range of the slopes of the linear least-square fittings, we concluded that BC concentrations regionally-representative of the area were measured in a range with a maximum-to-minimum ratio of 1.5 (an exception was that the BC (PM2.5) concentrations derived from MAAP were ~2 times higher than the optical measurements (PM2.5) derived from the ECOC analyzer). While this range is significant, it is still sufficiently narrow to better constrain the large and highly uncertain emission rate of BC from Central East China. In detail, two optical instruments (the MAAP and the PSAP equipped with a heated inlet 400°C) tended to give higher concentrations than the thermal EC concentrations observed by the ECOC analyzer. The ratios of optical BC to thermal EC showed a positive correlation with the OC/EC ratio reported by the ECOC analyzer, suggesting two explanations. One is that the optical instruments overestimated BC concentrations in spite of careful cancellation of the scattering effect in the MAAP instrument and the expected evaporation of volatile species by heating the inlet of the PSAP instrument. The other is that the determined split points between OC and EC were too late when a large amount of OC underwent charring during the analysis, resulting in an underestimation of EC by the ECOC analyzer. High ratios of optical BC to thermal EC were recorded when the NOx/NOy ratio was low, implying the coating of the particles became thicker in an aged air mass and thus resulted in the optical instruments overestimating BC concentrations because of the lensing effect.

A challenge for the quantitative analysis of tropospheric nitrogen dioxide (NO2) column data from satellite observations is posed partly by the lack of satellite-independent observations for validation. We performed such observations of the tropospheric NO2 column using the ground-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) technique in the North China Plain (NCP) from 29 May to 29 June, 2006. Comparisons between tropospheric NO2 columns measured by MAX-DOAS and the Ozone Monitoring Instrument (OMI) onboard the Aura satellite indicate that OMI data (the standard product, version 3) over NCP may have a positive bias of 1.6×1015 molecules cm−2 (20%), yet within the uncertainty of the OMI data. Combining these results with literature validation results for the US, Europe, and Pacific Ocean suggests that a bias of +20%/−30% is a reasonable estimate, accounting for different regions.

Citation: Irie, H., Kanaya, Y., Akimoto, H., Tanimoto, H., Wang, Z., Gleason, J. F., and Bucsela, E. J.: Validation of OMI tropospheric NO2 column data using MAX-DOAS measurements deep inside the North China Plain in June 2006: Mount Tai Experiment 2006, Atmos. Chem. Phys., 8, 6577-6586, 2008.

First attempt to correct model bias in a dust transport model using ensemble Kalman

filter (EnKF) assimilation targeting heavy dust episodes during the period of 15 – 24 March

2002 over north China is successfully performed. The uncertainty of dust emissions

and surface wind fields are taken into account individually and simultaneously to correct

their biases. The 24-h surface forecasts are significantly improved with the root mean

square error reduced by more than 45% on 20 March and by 50% on 21 March after

correcting the biases. The results indicate that there are high biases due to the dust

emissions and surface wind fields. These biases converge to the values similar with those

obtained in previous sensitivity analyses indicating that the EnKF can accurately correct

the bias. The corrected total dust emissions are decreased more than 33%. However,

when considered simultaneously, they do not converge to the same results as those

considered individually. This indicates that the two biases can compensate for each other

in terms of predicted surface dust concentration.

The impact of the East Asia monsoon on the seasonal behavior of O3 in the boundary layer of Eastern China and the west Pacific region was analyzed for 2004–2006 by means of full-year nested chemical transport model simulations and continuous observational data obtained from three inland mountain sites in central and eastern China and three oceanic sites in the west Pacific region. The basic common features of O3 seasonal behaviors over all the monitoring sites are the pre- and post-monsoon peaks with a summer trough. Such bimodal seasonal patterns of O3 are predominant over the region with strong summer monsoon penetration, and become weaker or even disappear outside the monsoon region. The seasonal/geographical distribution of the pre-defined monsoon index indicated that the East Asia summer monsoon is responsible for the bimodal seasonal O3 pattern, and also partly account for the differences in the O3 seasonal variations between the inland mountain and oceanic sites. Over the inland mountain sites, the O3 concentration increased gradually from the beginning of the year, reached a maximum in June, decreased rapidly to the summer valley in July or August, and then peaked in September or October, thereafter decreased gradually again. Over the oceanic sites, O3 abundance showed a similar increasing trend beginning in January, but then decreased gradually from the end of March, followed by a wide trough with the minimum in July and August and a small peak in October or November. A sensitivity analysis performed by setting China-emission to zero revealed that the chemically produced O3 from China-emission contributed substantially to the O3 abundance, particularly the pre- and post-monsoon O3 peaks, over China mainland. We found that China-emission contributed more than 40% to total boundary layer O3 during summertime (60–70% in July) and accounted for about 40 ppb of each peak value over the inland region if without considering the effect of the nonlinear chemical productions. In contrast, over the oceanic region in the high monsoon index zone, the contribution of China-emission to total boundary layer O3 was always less than 20% (<10 ppb), and less than 10% in summer.

http://www.atmos-chem-phys.net/8/7543/2008/acp-8-7543-2008.html

Tropospheric NO2 vertical column densities over East Central China (ECC) simulated with a regional air quality model are compared with those measured by the remote sensor SCIAMACHY (SCanning Imaging Absorption Spectrometer for Atmospheric CHartographY). A 3D Eulerian air quality model (Models-3/CMAQ) and a best available emission inventory are employed in the simulations. The objectives are to delve into (i) the suitability of the emission inventory employed, (ii) the reliability of SCIAMACHY observations over ECC, and (iii) the role of model resolution on predictions. The predicted NO2 concentrations are integrated from the bottom to the model top and converted from the model grid to satellite pixel bases. The model reproduces the spatial distribution of SCIAMACHY-observed NO2 vertical column densities satisfactorily with a correlation coefficient of about 0.76, but with a large normalized mean bias −60%. The latter bias is ascribed to the sharp increase of emissions that have occurred in ECC owing to rapid industrialization ever since the compilation of the emission inventory. When the model grid size is larger than the size of a satellite pixel, a decrease of grid size improves the CMAQ predictions when compared with SCIAMACHY, although higher resolutions in general do not necessarily improve CMAQ predictions. A critical cloud fraction of 0.2 is found to give the best comparisons between SCIAMACHY data and simulations.

Aerosol optical properties were continuously measured with the National Institute for Environmental Studies (NIES) compact Raman lidar over Beijing, China, from 15 to 31 December 2007. The results indicated that in a moderate pollution episode, the averaged aerosol extinction below 1 km height was 0.39+/-0.15 km −1 and the lidar ratio was 60.8+/-13.5 sr; in heavy pollution episode, they were 1.97+/-0.91 km −1 and 43.7+/-8.3 sr; in an Asian dust episode, they were 0.33+/-0.11 km −1 and 38.3 +/-9.8 sr. The total depolarization ratio was mostly below 10% in the pollution episode, whereas it was larger than 20% in the Asian dust episode. The distinct characteristics of aerosol optical properties in moderate and heavy pollution episodes were attributed to the difference in air mass trajectory and the ambient atmospheric

conditions such as relative humidity.

A coupled climate model is used to explore the response of the tropical sea surface temperature (SST) to positive SST anomalies in the global extratropics. The main model results here are consistent with previous numerical studies. In response to prescribed SST anomalies in the extratropics, the tropical SSTs rise rapidly and reach a quasi-equilibrium state within several years, and the tropical subsurface temperatures show a slow response. The annual-mean Hadley cell, as well as the surface trades, are weakened. The weakened trades reduce the poleward Ekman transports in the tropical ocean and, furthermore, lead to anomalous positive convergences of heat transport, which is the main mechanism for maintaining the tropical Pacific SST warming.

The process of an extratropical influence on the tropics is related to both the atmospheric and oceanic circulations. The intertropical convergence zone (ITCZ) moves southward and eastward in the Pacific, corresponding to a reduction of the Hadley circulation and Walker circulation. At the same time, convective precipitation anomalies are formed on the boundary of the climatological ITCZ, while the climatological mean convections centered in the Southeast Asia region are suppressed. The largely delayed response of the tropical subsurface temperature cannot be explained only by the strength change of the subtropical cells (STCs), but can be traced back to the slow changing of subsurface temperature in the extratropics. In the extratropical oceans, warming and freshening reduce the surface water density, and the outcropping lines of certain isopycnal layers are moved poleward. This poleward movement of outcropping lines can weaken the positive temperature anomalies, or even lead to negative anomalies, on given isopycnal layers. Displayed on time-dependent isopycnal layers, positive subsurface temperature anomalies are present only in the region after subduction, and are subsequently replaced by negative temperature anomalies in the deep tropics regions. The noticeable features of the density compensation of temperature and salinity indicate that diapycnal processes play an important role in the equatorward transport of the temperature and salinity anomalies from the midlatitude.

A new approach to forecast the middle-lower reaches of the Yangtze River Valley summer rainfall in

June―August (JJA) is proposed in this paper. The year-to-year increment of the middle-lower reaches

of the Yangtze River Valley is forecasted and hence the summer precipitation could be predicted. In this

paper, DY is defined as the difference of a variable between the current year and the preceding year

(year-to-year increment). YR denotes the seasonal mean precipitation rate of the middle-lower reaches

of the Yangtze River Valley summer rainfall. After analyzing the atmospheric circulation anomalies in

winter and spring that were associated with the DY of YR, six key predictors for the DY of YR have been

identified. Then the forecast model for the DY of YR is established by using the multi-linear regression

method. The predictors for the DY of YR are Antarctic Oscillation, the meridional wind shear between

850hPa and 200hPa over the Indo-Australian region, and so on. The prediction model shows a high skill

for the hindcast during 1997-2006, with the average relative root mean square error is at 18%. The

model can even reproduce the upward and downward trends of YR during 1984―1998 and 1998―2006.

Considering that the current operational forecast models of the summer precipitation over the China

region have the average forecast scores at 60%―70% and that the prediction skill for the middle-lower

reaches of Yangtze River Valley summer precipitation remains quite limited up to now, thus this new

approach to predict the year-to-year increment of the summer precipitation over the Yangtze River

Valley (and hence the summer precipitation itself) has the potential to significantly increase the operational

forecast skill of the summer precipitation.

The Climate Variability and Predictability (CLIVAR) program is one of the sub-programs of the World Climate Research Program (WCRP). In this paper, CLIVAR related research in China (2003{2006) is briely reviewed, including four major components, namely, low-frequency intraseasonal oscillations, interannual

variability, decadal variations in East Asia, and global warming simulations.

Relationships between the North Pacific Oscillation (NPO) and the typhoon as well as hurricane frequencies are documented. The correlation between NPO index in June-July-August-September and the annual typhoon number in the western North acific is 0.37 for the period of 1949―1998. The NPO is correlated with the annual hurricane number in the tropical Atlantic at − 0.28 for the same period. The variability of NPO is found to be concurrent with the changes of the magnitude of vertical zonal wind

shear, sea-level pressure patterns, as well as the sea surface temperature, which are physically associated

with the typhoons and hurricanes genesis. The NPO associated atmospheric circulation variability is analyzed to explain how NPO is linked with variability of the tropical atmospheric circulation in the western Pacific and the tropical Atlantic, via the atmospheric teleconnection.

　This paper briefly reviewed the studies of the relationships between the typhoon activity and the atmospheric circulation as well as the sea surface temperature in the first part . Then the authors int roduced some new research result s about the interannual variability and prediction of the typhoon climate,including the f requency of typhoon genesis and landfall , as well as the typhoon climate prediction by using both the numerical climate model and

the dynamical2statistical model. These researches relate the Antarctic oscillation, the North Pacific oscillation, sea ice coverage, and thermal state of the warm pool over the western Pacific. On the prediction aspect , the paper int roduced the first attempt to make the seasonal prediction of the typhoon climate by use of the climate model developed

at the Institute of Atmospheric Physics, Chinese Academy of Sciences, and a new dynamical2statistical model for the

prediction of the typhoon f requency.

Previous atmospheric general circulation model (AGCM) experiments revealed that atmospheric responses

to a tropical Atlantic sea surface temperature anomaly (SSTA) were asymmetric with respect to the

sign of the SSTA. A positive SSTA produced a south–north dipole in geopotential heights, much like the

North Atlantic Oscillation (NAO), while a negative SSTA yielded an eastward-propagating wave train, with

the northern lobe of the NAO absent.

Here these height responses are decomposed into components that are symmetric or antisymmetric with

respect to the sign of the SSTA. The symmetric, or notionally linear, component is a nearly south–north

dipole projecting on the NAO, while the antisymmetric, or notionally nonlinear, component is a different

dipole. Experiments with a diagnostic linear baroclinic model (LBM) suggest that both components are

maintained primarily by transient-eddy forcing. Dynamical mechanisms for the formation of the two components

are explored using the LBM and a nonlinear barotropic vorticity equation model (BVM). Transient-

eddy feedback is sufficient to explain the linear response. The NAO-like linear response occurs when

the initial heating induces transient-eddy forcing in the exit of the Atlantic jet. The structure of the

background absolute vorticity in this region is such that this transient-eddy forcing induces a nearly north–south dipole in anomalous geopotential heights. When the nonlinear self-interaction of this transient induced low-frequency perturbation is included in the BVM, the dipole axis tilts to the east or west,resulting in a response that is nonlinear about the sign of the forcing.

The Atlantic Multidecadal Oscillation (AMO), the multidecadal variation of North Atlantic sea surface

temperature (SST), exhibits an oscillation with a period of 65–80 years and an amplitude of 0.4C. Observational composite analyses reveal that the warm phase AMO is linked to warmer winters in East China, with enhanced precipitation in the north of this region and reduced precipitation in the south, on multidecadal time scales. The pattern is reversed during the cold phase AMO. Whether the AMO acts as a forcing of the multidecadal winter climate of East China is explored by investigating the atmospheric response to warm AMO SST anomalies in a large ensemble of atmospheric general circulation model (AGCM) experiments.

The results from three AGCMs are consistent and suggest that the AMO warmth favors warmer winters

in East China. This influence is realized through inducing negative surface air pressure anomalies in the hemispheric-wide domain extending from the midlatitude North Atlantic to midlatitude Eurasia. These negative surface anomalies favor the weakening of the Mongolian Cold High, and thus induce a weaker East Asian Winter Monsoon.

Relationship between the Antarctic oscillation (AAO) and the western North Pacific typhoon number (WNPTN) in the interannual variability is examined in this research. The WNPTN is correlated with the AAO in June-July-August-September (JJAS) in 1949－1998 at –0.48 for the detrended time series, statistically significant at 99% level. The tropical atmospheric circulation as well as the sea surface temperature variability over the western Pacificassociated with AAO has been analyzed. It follows that a positive phase of JJAS AAO corresponds to the larger magnitude of the vertical zonal wind shear, the anomalous low-lever anti-cyclonic circulation and anomalous high-level cyclonic circulation, and lower sea surface temperature in the major typhoon genesis region in the western North Pacific, thus providing unfavorable environment for the typhoon genesis, and vice versa.

研究了西北太平洋台风生成频次(WNPTN)和南极涛动(AAO)的关系, 发现6~9 月AAO 和西北太平洋台风生成频次(WNPTN)具有显著的反相关关系(1949~1998 年期间年际变化的相关系数为−0.48). 还分析了和AAO 的变化相联系的热带西太平洋大气环流和海温的变化, 结果表明: 当AAO 处于正位相时, 西北太平洋区纬向风的垂直切变幅度加大, 对流层低层为异常反气旋环流并且涡度异常为负值, 而高层为异常气旋环流并且涡度异常为正值, 海表温度降低, 这些变化均不利于台风生成和发展. 反之亦然.

Long-range transport of Asian dust and air pollutants are major environmental concerns of Taiwan during the winter monsoon season when northeasterly winds prevail following passages of cold fronts. Based on hourly measurements of Taiwan Environmental Protection Administration (TEPA) air quality monitoring stations, Lidar and insitu IC, a significant long-range transport dust and air pollutants event on 18 March 2005 has been identified. During this episode, drastically elevated concentrations of PM10, CO and SO2 along with the strong northeasterly on 18 March were observed over background Wanli station, with peaks of about 170μgm−3, 1.0 ppm and 14 ppb, respectively. We have found that air masses of air pollutants and Asian dust are transported separately. Although the mixing takes place on the way to Taiwan, it mixes slightly when they arrived in Taiwan. The major component of the first PM10 peak were air pollutants, evidenced by the consistent peaks of SO2− 4 and NO−3 measured by in-situ IC, while no significant depolarization was measured by Lidar. In contrast, the evident non-spherical particles and hourly PM10 concentration consistently varied with Ca2+ indicating that mineral dust was the major component of the second peak. Trajectory analysis showed that these two peaks come from quite different sources areas. The air masses of the first peak mainly come from anthropogenic area and transport in the low boundary layer (<1500 m) while the masses of the second peak originate from high altitude (>4000 m) of desert areas. Numerical results showed significant agreement of temporal and vertical variation of aerosol concentration with observations. The phenomena of split air parcels between air pollutants and Asian dust transported to Taiwan are strongly associated with the transport paths and stable and dry atmospheric boundary conditions.

The short-lived reactive specimen nitrous acid HONO was generated in the gas phase by the heterogeneous

reaction of gaseous HCl with AgNO2 which can generate higher concentration of HONO than

other methods. We investigated the process from generation to dissociation in the gas phase under

different controlled temperatures, and discussed the ionization and reaction on the solid surface by

combination of the photoelectron spectroscopy and photoionization mass spectroscopy (PES-PIMS)

and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS).

On the basis of three mountain sites (Mount Tai, Hua and Huang) newly founded in east-central China and several other sites from the Acid Deposition Monitoring Network in east Asia (EANET) and WMO World Data Centre for Greenhouse Gases(WDCGG), we investigate seasonal cycle of ozone over east Asia and its budgets in east-central China by using a regional chemical transport model (NAQPMS). The

observations show a striking ozone pattern of two sharp peaks in May-June and September–October at three mountain sites in east-central China which are higher than those observed at other mountain sites in Europe and North America. Ozone budgets analysis by the model confirms that maximum of net photochemical productions reaches 31.8, 15.1, and 11.4 ppbv/d at Mount Tai, Hua, and Huang, respectively. The net photochemical production dominates the formation of ozone maximums at Mount Tai and Hua in June, and the importing transport also plays a comparable importance at Mount Huang. In comparison with those in the western North Pacific, east-central China shows stronger net photochemical productions, which are comparable to

anthropogenic sources regions in Europe and North America.

The transport and mixing of dust aerosols and pollutants in East Asia during March 18 to 22, 2002 was studied using the nested air quality prediction

model system (NAQPMS). Dust was primarily generated in the Gobi desert on 19 March and then swept across several areas of East Asia. The model results were verified with observations of surface weather, TSP/PM10, SO2 and lidar data. The model simulated the right timing and strength of dust events, capturing most of the variation features in dust and SO2. Numerical results showed that the dust aerosols were mainly transported in two layers and mixed with pollutants in different ways. Some of the dust

kicked up in the source region was uplifted to a higher layer (200 - 2000 m layer) and transported downwind faster than dust of the lower level. This

lower-level dust was of greater concentration. The dust arriving at the upper layer began to drop and mixed well with pollutants in the atmosphere during “the first period”. During “the second period”, pollutants were diluted by the dust air mass that was transported along the lower layer. The remaining pollutants mixed well with dust aerosols during this period. The mixed air mass of the higher layer (1500 m) eventually reached the Northwestern Pacific. A large amount of clouds in the upper layers potentially led to an increase in sulfate mass on the surface of dust particles.

Elevated ozone concentration is one of the current major environmental concerns in Taiwan. The spatial distribution and seasonal variations of ground level ozone over Taiwan are investigated by using air quality network stations of Taiwan Environmental Protection Administration (TEPA). Data shows that high ozone episodes frequently occur over southwest Taiwan during autumn. In this season, shallow northeasterly winds prevail after frontal passage and are diverted by the Central Mountain Range (CMR) because of its mean altitude of about 2.5 km. The windward side in northern Taiwan is usually associated with cloudy days, whereas sunny days with weak wind speeds usually occur on the lee side of the CMR over southwest Taiwan due to topographical blocking. Numerical results indicate that anthropogenic emissions from the north of Kaohsiung could contribute as much as 41% of ozone for the Kaohsiung metropolitan area and 24% for the inland rural Pingtung area during the northerly flow. It is concluded that the contribution of the emissions from the north of Kaohsiung is significant and cannot be ignored. The northerly air masses, which flows over the western plain during daytime, picks up ozone and its precursors which are transported to southwestern Taiwan. After a sea breeze develops, strong onshore flow transports significant amounts of ozone and precursors to the inland rural areas resulting in the high ozone episodes that frequently occur over southwestern Taiwan during the autumn season.

In this paper, the impacts of the atmospheric circulation during boreal winter-spring on the western North Pacific (WNP) typhoon frequency (WNPTF) are studied. Several new factors in winter-spring in-fluencing the typhoon frequency were identified, including the sea ice cover in the North Pacific and the North Pacific oscillation. Based on these results, the multi-linear regression was applied to establishing a new forecast model for the typhoon frequency by using the datasets of 1965―1999. The forecast model shows a high correlation coefficient (0.79) between the model simulated and the actual typhoon frequencies in the period of 1965―1999. The forecast model also exhibits reasonable hindcasts for the typhoon frequencies for the years 2000―2006. Therefore, this work demonstrates that the new pre-dictors are significant for the prediction of the interannual variability of the WNPTF, which could be potentially used in the operational seasonal forecast of the typhoon frequency in the WNP to get a more physically based operational prediction model and higher forecast skill.

In this research, the zonal asymmetry of the southern

annular mode, or the Antarctic Oscillation (AAO), is

studied. It is indicated that apparent zonal asymmetry

exists in the normalized sea level pressure differences

between the middle and high latitudes during the boreal

summer, among different longitudes, especially between

the Western and Eastern Hemispheres. Results show that

the Southern Oscillation (SO) is responsible for part of

the zonal asymmetry in AAO. The Western Hemisphere

and the Eastern Hemisphere parts of AAO are correlated

at 0.23 and 0.52 respectively for the period of 1959–

1998 before and after the linear regressions on the

Southern Oscillation Index (SOI) have been removed

from the time series. The paper also discusses the

relationship between the precipitation in the East Asia and

the AAO before and after removing the linear regressions on

SO index (SOI), indicating the stable relationship between

the East Asian precipitation and the zonal symmetric

component of AAO

The relationship between the sea ice cover in the North Pacific and the typhoon frequency has been

studied in this paper. It follows that the index for the sea ice cover in the North Pacific (ISA) both in

December-January-February (DJF) and in March-April-May (MAM) is negatively correlated with annual

typhoon number over the western North Pacific (TNWNP) during 1965―2004, with correlation coefficients

of −0.42 and −0.49 respectively (above 99% significant level). Large sea ice cover in the North

Pacific tends to decrease TNWNP. Positive ISA (MAM) is associated with the tropical circulation and

SST anomalies in the North Pacific, which may lead to unfavorable dynamic and thermal conditions for

typhoon genesis over WNP from June to October (JJASO). The variability of the atmospheric circulation

over the North Pacific, associated with the ISA anomaly in MAM is connected to the tropical atmospheric

circulation variability in MAM via the teleconnection wave train. Besides, as the tropical

circulation has strong seasonal persistency from the MAM to JJASO, thus, the ISA in MAM-related

variability of the tropical atmospheric circulation as well as the SST can affect the typhoon activity over

the western North Pacific.

Relationships between the North Pacific Oscillation (NPO) and the typhoon as well as hurricane frequencies

are documented. The correlation between NPO index in June-July-August-September and the

annual typhoon number in the western North Pacific is 0.37 for the period of 1949―1998. The NPO is

correlated with the annual hurricane number in the tropical Atlantic at − 0.28 for the same period. The

variability of NPO is found to be concurrent with the changes of the magnitude of vertical zonal wind

shear, sea-level pressure patterns, as well as the sea surface temperature, which are physically associated

with the typhoons and hurricanes genesis. The NPO associated atmospheric circulation variability

is analyzed to explain how NPO is linked with variability of the tropical atmospheric circulation in

the western Pacific and the tropical Atlantic, via the atmospheric teleconnection.

The East Asian climate at the Last Glacial Maximum (LGM, 21,000 years B.P.) has been simulated using a regional climate model (RegCM2) nested in an atmospheric general circulation model of the Institute of Atmospheric Physics (IAP-AGCM).

Boundary conditions for the LGM simulations are consistent with the Paleoclimate Modelling Intercomparison Project (PMIP). The results show that the nested regional model reproduces well the colder LGM climates over East Asia. The simulated annual mean surface temperature is 2 °C–4 °C colder than the present over the East Asian continent, with the coldest anomaly of about 8 °C in the vicinity of current coastal areas, where land is exposed due to lowering sea level at the LGM. The precipitation changes are complex, with general features of drier conditions over eastern China and its neighborhood and wetter conditions over western China than the present. Compared with the driving IAP-AGCM, the RegCM2 results display better agreement with geological reconstructions over East Asia. Especially in the mideastern and southern China, the simulated warming changes by the IAPAGCM disagree with cooling in paleodata, whereas the RegCM2 reproduces realistic cooler LGM climate. Thus the current work proves that the high-resolution RegCM2 can capture additional regional details in the LGM simulation, produced by improved representation of topography and physics.

The relationship between the Pacific

Decadal Oscillation (PDO) and the Arctic Oscillation (AO) on decadal timescale in the extended winter (November－March) is investigated in this study. The results indicate that AO plays an important role in the low frequency variability of PDO. When AO leads PDO by 7－8 years, the lagging correlation between them becomes the strongest with correlation coefficient

0.77. The leading decadal variability of AO provides a valuably precursory signal for predicting the variability of PDO. The results of regression and lagging

correlation reveal the possible mechanism for the AO-PDO coupling: A strong AO ould lead to an enhanced Aleutian Low that is linked to PDO by ocean-atmosphere interaction in the North Pacific, and vice versa.

This paper reports the first real—time climate numerical experiment aiming at the prediction of the typhoon frequency in the western North Pacific(W NP)for the current year 2006．The prediction results show that the convective activities are reduced，the magnitude of the vertical zonal wind shear is increased，and there are anomalous high level convergence and low-level divergence during the June-October in the WNP．The predicted sea sur

face temperature anomalies in W NP are very smal1．Therefore，the results suggest that there maybe less typhoon

genesis in W NP compared to the normal years．However，there are uncertainties in the prediction because of the

complexity in the typhoon genesis and development in the region.

Based on the observational data of 23 stations in Northeast China during 1951-2000, the temporalspatial distributions of summer air temperature (SAT) are investigated. It is found that the variabilities of SAT are different in the north and south of Northeast China on the interannual and decadal time scales, besides the same variability in the whole region. And the SAT in the north exhibits a significantly abrupt climate change in

19871988. Except for the years with the same variability, the relationships between the SAT in the two areas and atmospheric general circulation as well as sea surface temperature (SST) are revealed as follows: before the abrupt climate change, the main features of the atmospheric general circulation and SST associated with the two areas’ SATs are different. The key sea regions which have influence on the SAT in the south area (SA) are the mid-latitude western Pacific and parts of the Indian Ocean. On the other hand, the main factor for the north

area (NA) is ENSO events. After the abrupt climate change, the variabilities of the SATs in the two areas and

the corresponding atmospheric circulation and SST anomalous patterns become imilar. In addition, the NA SAT has a significant correlation with the East Asian Summer Monsoon (EASM) during 19512000, but the high correlation does not exist in the SA.

The leading pattern of Northern Hemisphere winter height variability exhibits an annular structure, one

related to tropical west Pacific heating. To explore whether this pattern can be excited by tropical Pacific SST variations, an atmospheric general circulation model coupled to a slab mixed layer ocean is employed. Ensemble experiments with an idealized SST anomaly centered at different longitudes on the equator are conducted. The results reveal two different response patterns—a hemispheric pattern projecting on the annular mode and a meridionally arched pattern confined to the Pacific–North American sector, induced by the SST anomaly in the west and the east Pacific, respectively. Extratropical air–sea coupling enhances the annular component of response to the tropical west Pacific SST anomalies.

A diagnosis based on linear dynamical models suggests that the two responses are primarily maintained by transient eddy forcing. In both cases, the model transient eddy forcing response has a maximum near the exit of the Pacific jet, but with a different meridional position relative to the upper-level jet. The emergence of an annular response is found to be very sensitive to whether transient eddy forcing anomalies occur within the axis of the jet core. For forcing within the jet core, energy propagates poleward and downstream,inducing an annular response. For forcing away from the jet core, energy propagates equatorward and downstream, inducing a trapped regional response. The selection of an annular versus a regionally confined tropospheric response is thus postulated to depend on how the storm tracks respond. Tropical west Pacific SST forcing is particularly effective in exciting the required storm-track response from which a hemispherewide teleconnection structure emerges.

The coupled ocean-atmosphere response to Indian

Ocean warmth is studied. It is shown with atmospheric

models that Indian Ocean warmth forces a positive polarity phase of the North Atlantic Oscillation(NAO), confirming results of previous studies. Coupled model experiments show that this NAO response forces a local air-sea feedback over the North Atlantic Ocean, which intensifies the NAO

response. This enhancement is realized through a positive feedback between the NAO atmospheric circulation anomaly and a tripolar North Atlantic SST pattern,consistent with other studies on North Atlantic air-sea interactions. It is concluded that the North Atlantic and European climate response to Indian Ocean warming may be considerably greater than hitherto judged from the analyses of atmospheric model experiments alone.

The Southern Hemisphere (SH)atm ospheric circulation is both an important compo nent of the global general circulation and a key factor influencing the global climate change and Asian monsoon systems． In early times，Chinese meteorologists focused the role of SH in the East Asia summer monso n and obtain important resuits．Studies of the SH clima te variability are currently paid much attention by meteorologists in the world．In recent years，meteorologists have been doing researches on the SH interannal variability and its association with East Asian Climate，with special focus on the Antarctic Oscillation(AAO)and the subtropical high pressure systems in SH．Besides，studies of the relationship between SH and bo th Ea st Asian clima te and dust during bo real winter and spring have been paid much attention as wel1．This paper introduces recent studies including the relationship between the interannual variability of AAO and dust weather frequency(DW F)in North China and Ea st Asian climate during boreal winter and spring ；central North China precipitation based on the reconstructed data from the Qing Dynasty；the summer rainfall over the Yang tze River valley，as well as the reproducibility of variability of AAO．

Potential future research focuses are also discussed in the paper．Recent results show that the interannual variation of AAO plays a significant role in the dust-related atmospheric circulation during bo real spring． AAO and DWF correlate well，with po sitive AAO tending to decrease DW F in North China. Two possible mechanisms for the AAO-DWF couDling are identified：one is related to a meridional telecormection pattern the other lS related tO a regional

circulation pattem over the Pacific Ocean．The positive AAO anomaly decreases the cold activity over East Asia during boreal winter and spring． AAO-related barotropic meridional teleconnection from Antarctic to Arctic is found through analysis of mean meridional circulations． This meridional teleconnection is remarkable over Eurasia area during bo real wimer and over the Pacific Ocean during boreal spring． Based on analysis of the long -term central North China precipitation(CNCP)time series reconstructed from the Qing Dynasty official document，it is found that the AAO is negatively correlated with the CNCP during June-July．It follows that AAO-related variability of convergence and convection over the tropical western Pacific can exert impact on the circulation condition and precipitation in north China(actually，the precipitation in the Yangtze River valley as well through atmospheric teleconnection known as the East Asia-Pacific(or Pacific Japan teleconnection wave pattern．Researches show that the interannua1 of Mascarene high(M H)and Australian high(AH)in bo real spring may provide some useful informationfor the Ea st Asian summer monsoon precipitation． With the intensification of MH during bo real spring through summer，the Meivu rain tends to increase while the effect of AH on summer rain is COnfined to southern China． Its physical mechanisms are related to change of convection near the Philippines．The reproducibility of variability of AAO iS another foCUS．Using the NCAR CAM2 model forced with the historical Sea surface temperature covering the period of 1950—2000，there would be some predictability to the AAO．The reproducibility is greater during the austral summer than winter. and the source of much of reproducibility iS the tropical Pacific SST．Besides, Sea temperatureat high latitudes of SH may force the AAO during bo real spring using IAP9L-AGCM model. However, the issues on the relationships between the So uthern Hemisphere circulation and Ea st Asian climate still need be studied further．

Rlationship between the Southern Hemisphere upper troposphere zonal wind variability and the East Asian summer monsoon was studied. The mean zonal wind difference in 150 hPa between 60°S and 30°S is defined as an index (ISH). The re-search reveals that ISH is negatively correlated with the East Asian summer monsoon (EASM) circulation in the interannual scale. It is also suggested that the meridional teleconnection in the zonal wind field, with the main part in Eastern Hemisphere, from mid-and-high latitudes in the Southern Hemisphere to the tropical region is responsible for the ISH-EASM linkage. The teleconnection may result in changes of the wind fields and pressure system changes causing variability of the East Asian monsoon. In addition, the anomalous teleconnection pattern in Eurasia is likely to be another mechanism. ISH and EASM circulation are found to have both simultaneous and lag correlations, thus, the relationship has implications for sea-sonal climate prediction over East Asia.

The interannual variability of Antarctic Oscillation (AAO) and its influence on East Asian climate during both boreal winter and spring are addressed. The results show that the positive AAO anomaly decreases the cold activity over East Asia during both boreal winter and spring. AAO-related barotropic meridional teleconnection from Antarctic to Arctic is found through analysis of mean me-ridional circulations. This meridional teleconnection is remarkable over Eurasia during boreal winter and over the Pacific Ocean during boreal spring. The results also show that zonal mean zonal wind at high latitudes in Southern Hemisphere has well positive correlation with that of Eurasia during boreal winter and has negative correlation with Pacific North American teleconnection (PNA) during boreal spring, which again display the meridional teleconnection. Thus, local meridional teleconnection is a possible linkage for interaction of circulations at mid-high latitudes between both hemispheres.

The long-term relationship between the tree-ring-reconstructed annual precipitation in northeastern

Mongolia (PRM) and the Northern Hemisphere Zonal Circulation (NHZC)§defined as the normalized

zonal mean sea-level pressure at 60N in May-June-July, is examined in this study. A significant correlation

coefficient (0.31) was found between the NHZC indices and PRM based on the dataset for the

period of 1872–1995. The mechanisms responsible for the relationship are discussed through analyses of

the atmospheric general circulation variability associated with NHZC. It follows that NHZC-related atmospheric

circulation variability provides an anomalous southeast flow from the ocean to Northeast Mongolia

(northwest flow from Northeast Mongolia to the ocean) in the middle and low troposphere in positive

(negative) phase of NHZC, resulting in more (less) water vapor transport to the target region and more

(less) precipitation in Northeast Mongolia.

Geological research has illustrated the transition of palaeoenvironmental patterns by the earliest Miocene from a planetary-wind-dominant type to a monsoon-dominant type, indicating that the East Asian monsoon became markedly intensified and played a leading role in the East Asian climate. From a modeling point of view, the pioneering research using the reduced number of scenarios had demonstrated that both the Tibetan Plateau uplift and the Paratethys Sea retreat were important for understanding the Asian monsoon evolution. However, the sensitivity of the Paratethys retreat to the East Asian climate still needs further studies based on the more detailed scenarios. Thirty numerical experiments under the six Paratethys Sea and the five Tibetan Plateau conditions illustrate the shifts from zonal climate to the monsoon climate in East Asia. The results confirm again that both the Paratethys retreat and the Tibetan plateau uplift play important roles in the formation of the monsoon-dominant environmental pattern, and show that the Paratethys retreat can strengthen the East Asian monsoon and greatly increase humidity and aridity respectively in the monsoon areas and Northwest China, which is similar to the impact of the Tibetan Plateau uplift on the East Asian climate. Furthermore, the fact that the Paratethys Sea retreats to the Turan Plate is found to be the key criterion for the palaeoenvironmental patterns' transition in China. The shrinkage of Paratethys Sea leads to the reconstructions of the pressure system and the atmospheric circulations, which result in the variations of precipitation and the transition of palaeoenvironmental patterns.

A high O3 episode was observed during 23–25 May 2004 at two high-mountain sites reflecting the regional pattern of air pollutants over East China. This episode lasted about three days with the maximum hourly O3 mixing ratios reaching 111 and 114 ppbv at Mt. Tai and Huang, respectively. Backward trajectories and meteorological analysis indicated that regional transport, associated with a weak high pressure system over the East China Sea, might play an important role in the formation of this high ozone episode. The nested air quality prediction modeling system (NAQPMS) was applied to investigate the formation and evolution of this high O3 event. The comparison of model results with observations showed that NAQPMS successfully reproduced the main observed patterns of O3 and meteorological parameters during the simulated period. The model results with emission over the Yangtze Delta and the East Central China switched on/off clearly showed that ozone and its precursors transported from the Yangtze Delta and the East Central China enhanced the high ozone episode at two sites, with a contribution of 20% –50% during the episode. In addition, based on process analysis with the model, chemical production and regional transport appeared to be the main causes of high ozone episode involving a large amount of high-ozone air masses and precursors transported from the surrounding areas. The horizontal transport is more active during the period of high ozone episode than that during the non-episode at Mt. Tai as well as Mt. Huang.

The relationship between long-term variation of Asian dust and climate indices was studied using a regional scale dust-transport model. Simulation results were examined using visibility-based observations by Chinese and Japanese Meteorological Agencies. Those results showed that the model reasonably captured interannual variations of Asian dust during 1972–2004. The long-term trend of dust days in the Gobi desert region showed a remarkable declining trend from the early 1980s–1997; the increasing trend of recent years (2000–02) was more conspicuous in Japan. Analyses of time variation of meteorological parameters in the Gobi region showed that the decreasing trend of dust days in this region is explained by the decreased frequency of strong winds. Additionally, anomaly analyses for dust and meteorological parameters in the Gobi region indicated that invasion of polar cold air played an important role in increasing dust phenomena. To clarify climate factors that affect dust emission and transport, regional climate indices that are appropriate for the scale of Asian dust storms were newly introduced. Correlation analyses between climate indices and simulated dust emissions showed that the dominant climate indices, which are closely correlated with dust emissions, were different in March and April. In March, the climate indices related to divergence of cold air from the polar region to mid-latitudes displayed a strong correlation with dust emissions, but during April, the climate index related to the south-north pressure gradient over the Gobi region exhibited a strong correlation with dust emission. Analyses of correlation between simulated surface dust concentrations and the Southern Oscillation Index (SOI) suggest that the El Niño/Southern Oscillation (ENSO) affects the dust transport path. Analyses of average dust transport flux at 130°E clarified variation of the transport path between La Niña years and El Niño years.

An intercomparison study involving eight dust emission/transport models over Asia

(DMIP) has been completed. Participating dust models utilize a variety of dust emission

schemes, horizontal and vertical resolutions, numerical methods, and different

meteorological models. Two huge dust episodes occurred in spring 2002 and were used

for the DMIP study. Meteorological parameters, dust emission flux and dust concentration

(diameter < 20 mm) are compared within the same domain on the basis of PM and NIES

lidar measurements. We found that modeled dust concentrations between the 25% and

75% percentiles generally agreed with the PM observations. The model results correctly

captured the major dust onset and cessation timing at each observation site. However, the

maximum concentration of each model was 2–4 times different. Dust emission fluxes

from the Taklimakan Desert and Mongolia differ immensely among the models, indicating

that the dust source allocation scheme over these regions differs greatly among the various

modeling groups. This suggests the measurements of dust flux and accurate updated land use

information are important to improve the models over these regions. The dust vertical

concentration profile at Beijing, China, and Nagasaki, Japan, has a large scatter (more than

two times different) among the models. For Beijing, the scaled dust profile has a quite similar

vertical profile and shows relatively good agreement with the lidar extinction profile.

However, for Nagasaki, the scaled dust profiles do not agree. These results indicate that

modeling of dust transport and removal processes between China and Japan is another

important issue in improving dust modeling.

Citation: Uno, I., et al. (2006), Dust model intercomparison (DMIP) study

Because concentrations of fine particulate matter (PM) and ozone in Beijing often exceed

healthful levels, China is to taking steps to improve Beijing’s air quality for the

2008 Olympic Games. In this paper the Models-3 Community Multiscale Air Quality

(CMAQ) 5 Modeling System was used to investigate a heavy air pollution episode in Beijing

during 3–7 April 2005. The modeling domain covered from East Asia with four

nested grids with 81 to 3km horizontal resolution focusing on urban Beijing. This was

coupled with a regional emissions inventory with a 10 km resolution and a local 1 km

Beijing emissions database. The trend of predicted concentrations of various pollutants

10 agreed reasonably well with the observations and captured the main features of this

heavy pollution episode. The simulated column concentration distribution of PM was

correlated reasonably with the MODIS remote sensing products. Control runs with and

without Beijing emissions were conducted to quantify the contributions of non-Beijing

sources (NBS) to the Beijing local air pollution. The contributions of NBS to each

15 species differed spatially and temporally with the order of PM25>PM10>SO2>SOIL for

this episode. The percentage contribution of NBS to fine particle (PM2.5) in Beijing was

averaged about 40%, up to 80% at the northwest of urban Beijing and only 10–20% at

southwest. The spatial distribution of NBS contributions for PM10 was similar to that for

PM2.5, with a slightly less average percentage of about 30%. The NBS contributions for

20 SO2 and SOIL (diameter between 2.5 μm and 10 μm) were only 10–20% and 5–10%.

In addition, the pollutant transport flux was calculated and compared at different levels

to investigate transport pathway and magnitude. It was found that the NBS contribution

correlated with the transport flux, contributing 70% of PM10 concentration in Beijing

at the time of transport flux peak during a strong episode with a transport path from

25 southwest to northeast.

Long-range transport of Asian dust and air pollutants are major environmental concerns

of Taiwan during the winter monsoon season when northeasterly winds prevail

following passages of cold fronts. Based on hourly measurements of Taiwan Envi-

5 ronmental Protection Administration (TEPA) air quality monitoring stations, Lidar and

in-situ IC, a significant long-range transport dust and air pollutants event on 18 March

2005 has been identified. During this episode, drastically elevated concentrations of

PM10, CO and SO2 along with the strong northeasterly on 18 March were observed

over background Wanli station, with peaks of about 170 μgm−3, 1.0PPM and 14 ppb,

10 respectively. We have found that air masses of air pollutants and Asian dust are transported

separately. The major component of the first PM10 peak were air pollutants,

evidenced by the consistent peaks of SO2− 4 and NO−3 measured by in-situ IC, while no

significant depolarization was measured by Lidar. In contrast, the evident non-spherical

particles and hourly PM10 concentration consistently varied with Ca2+ indicating that

15 mineral dust was the major component of the second peak. Numerical results showed

significant agreement of temporal and vertical variation of aerosol concentration with

observations. The phenomena of split air parcels between air pollutants and Asian

dust transported to Taiwan are strongly associated with the transport paths and stable

and dry atmospheric boundary conditions.

Systematic analyses of interannual and seasonal variations of tropospheric NO2 vertical

column densities (VCDs) based on GOME satellite data and the regional scale

chemical transport model (CTM), Community Multi-scale Air Quality (CMAQ), are presented

over 5 eastern Asia between 1996 and June 2003. A newly developed yearby-

year emission inventory (REAS) was used in CMAQ. The horizontal distribution of

annual averaged GOME NO2 VCDs generally agrees well with the CMAQ results. However,

CMAQ/REAS results underestimate the GOME retrievals with factors of 2–4 over

polluted industrial regions such as Central East China (CEC), a major part of Korea,

10 Hong Kong, and central and western Japan. For the Japan region, GOME and CMAQ

NO2 data show good agreement with respect to interannual variation and show no

clear increasing trend. For CEC, GOME and CMAQ NO2 data show good agreement

and indicate a very rapid increasing trend from 2000. Analyses of the seasonal cycle

of NO2 VCDs show that GOME data have systematically larger dips than CMAQ NO2

15 during February–April and September–November. Sensitivity experiments with fixed

emission intensity reveal that the detection of emission trends from satellite in fall or

winter have a larger error caused by the variability of meteorology. Examination during

summer time and annual averaged NO2 VCDs are robust with respect to variability of

meteorology and are therefore more suitable for analyses of emission trends. Analysis

20 of recent trends of annual emissions in China shows that the increasing trends of 1996–

1998 and 2000–2002 for GOME and CMAQ/REAS show good agreement, but the rate

of increase by GOME is approximately 10–11% yr−1 after 2000; it is slightly steeper

than CMAQ/REAS (8–9% yr−1). The greatest difference was apparent between the

years 1998 and 2000: CMAQ/REAS only shows a few percentage points of increase,

25 whereas GOME gives a greater than 8%yr−1 increase. The exact reason remains unclear,

but the most likely explanation is that the emission trend based on the Chinese

emission related statistics underestimates the rapid growth of emissions.

TSP and PM2.5 aerosol samples were synchronously collected at six sites along the

transport pathway of dust storm from desert regions to coastal areas in the spring of

2004. The aerosol concentration and composition were measured to investigate the

5 regional characteristics of spring Asian dust and its impact on aerosol chemistry over

northern China. Based on the daily PM10 concentrations in 13 cities, the northern

China could be divided into five regions, i.e., Northern Dust Region, Northeastern Dust

Region, Western Dust Region, Inland Passing Region, and Coastal Region. Northern

Dust Region was characterized by high content of Ca and Northeastern Dust Region

10 was characterized by low one instead. Northeastern Dust Region was a relatively

clean area with the lowest concentrations of pollutants and secondary ions among

all sites. Inland Passing Region and Coastal Region showed high concentrations of

pollutants, of which As and Pb in Inland Passing Region, and Na+, SO2− 4 , and NO−3 in

Coastal Region were the highest, respectively. The impact of dust on air quality was

15 the greatest in the cities near source regions, and this impact decreased in the order of

Yulin/Duolun > Beijing > Qingdao/Shanghai as the increase of transport distance. The

spring Asian dust was inclined to affect the chemical components in coarse particles

near source regions and those in fine particles in the cities far from source regions.

Dust storm could mix significant quantities of pollutants on the pathway and carry them

20 to the downwind cities or dilute the pollutants in the cities over northern China. Each

dust episode corresponded to a low ratio of NO−3 /SO2− 4 with the lowest value appearing

after the peak of dust storm. Asian dust played an important role in buffering and

neutralizing the acidity of atmosphere in the cities over northern China, which could

lead to the pH in the aerosols increase 1 in spring.

The relationship between long-term variation of Asian dust and climate indices was studied using a regional scale dusttransport

model. Simulation results were examined using visibility-based observations by Chinese and Japanese

Meteorological Agencies. Those results showed that the model reasonably captured interannual variations of Asian dust

during 1972–2004. The long-term trend of dust days in the Gobi desert region showed a remarkable declining trend from

the early 1980s–1997; the increasing trend of recent years (2000–02) was more conspicuous in Japan. Analyses of time

variation of meteorological parameters in the Gobi region showed that the decreasing trend of dust days in this region is

explained by the decreased frequency of strong winds. Additionally, anomaly analyses for dust and meteorological

parameters in the Gobi region indicated that invasion of polar cold air played an important role in increasing dust

phenomena. To clarify climate factors that affect dust emission and transport, regional climate indices that are appropriate

for the scale of Asian dust storms were newly introduced. Correlation analyses between climate indices and simulated dust

emissions showed that the dominant climate indices, which are closely correlated with dust emissions, were different in

March and April. In March, the climate indices related to divergence of cold air from the polar region to mid-latitudes

displayed a strong correlation with dust emissions, but during April, the climate index related to the south-north pressure

gradient over the Gobi region exhibited a strong correlation with dust emission. Analyses of correlation between simulated

surface dust concentrations and the Southern Oscillation Index (SOI) suggest that the El Nin˜ o/Southern Oscillation

(ENSO) affects the dust transport path. Analyses of average dust transport flux at 1301E clarified variation of the transport

path between La Nin˜ a years and El Nin˜ o years.

The Models-3 Community Multi-scale Air Quality (CMAQ) modeling system with meteorological fields calculated by

the Regional Atmospheric Modeling System (RAMS) was applied to East Asia to investigate the transport and

photochemical transformation of tropospheric ozone during the Transport and Chemical Evolution over the Pacific

(TRACE-P) field campaign. Modeled concentrations of hydroxyl radical, hydroperoxyl radical, nitric oxide, nitrogen

dioxide, ethene, ethane, carbon monoxide, and ozone were compared with observations obtained onboard of two aircrafts

in order to evaluate the model performance. Comparison indicates that the model reproduced the tempo-spatial

distributions of ozone and its related chemical species reasonably well, and most model results were within a factor of 2 of

the observations.

A ten-year simulation of present climate over East Asia was conducted with the RegCM2 which is

nested in a gridpoint general circulation model (IAP-AGCM) developed by IAP/CAS (Institute of Atmospheric

Physics, Chinese Academy of Sciences) in one-way mode, and model results are tested and analyzed. It shows that the RegCM2 has a reasonable ability to simulate spatial distributions and seasonal cycles of surface air temperature and precipitation, due to its high resolution and perfect physics course. Compared with the IAPAGCM, the RegCM2 achieves much improvement. The spatial correlation coefficient (SCC) of annual surface air temperature increases from 0.92 to 0.94 and SCC of annual precipitation increases from 0.5 to 0.7 over China. One of the reasons is that the nested RegCM2 can capture mesoscale signals caused by sub-GCM grid scale forcings, which exist in observations but not in the IAP-AGCM.

Key words Regional climate model, One-way nesting, Simulation over East Asia, Mesoscale signals

The Circum-Pacific Teleconnection Pattern (CPTP) is revealed in the meridional wind in the high troposphere via an emprirical orthogonal function (EOF) and correlation analysis on NCEP/NCAR reanalysis data. The CPTP is found to be composed of the North Pacific–North American teleconnection pattern (PNA), the South Pacific–South American teleconnection pattern (PSA), and the teleconnection patterns over the tropical western Pacific and the tropical eastern Pacific (or, Central America, or, tropical Atlantic). There is substantial interannual variability of the CPTP and a typical CPTP can be detected in some years. It is speculated that the zonal wind anomalies over the equatorial region in the western and eastern sides of the Pacific may play a role in linking the two hemispheres. The anomalous convection activities in the Tropics are plausible triggering factors for the zonal wind anomalies that are responsible for the composition of the CPTP.

　This is a very preliminary work on detection of seasonal climate predictability arising from the internal atmosphere. Generally speaking, seasonal climate predictability is mostly determined by the external forcing that has larger scale of temporal variation, namely, the sea surface temperature, snow cover, soil wetness, and so on. Based on analyzing the persistence of monthly mean wind anomalies and the East Asian monsoon-related global-scale atmospheric circulation anomalies, the inner-atmosphere-originated seasonal climate predictability is discussed. The results show that the wind anomalies in spring in many key regions like upper troposphere and lower stratosphere in the tropics, which isclosely related to the East Asian monsoon , may persist for up to 4 to 5 months. Thus, climate predictability may be partly originated by the internal processes of the atmosphere.

Based on the reanalysis data throughout 1948―2002 as derived from the United States National Centers for Environmental Prediction and National Center for Atmos-pheric Research, it is revealed that East Asian summer mon-soon (EASM) intensity weakens on an interdecadal timescale since the mid-1960s, and twice interdecadal jumps are re-corded in the EASM intensity index series in the late 20th century, respectively occurring in the mid-1960s and mid- to late 1970s. Six globally coupled atmosphere-ocean models’ outputs under the SRES A2 greenhouse gas and aerosol emission scenario, provided by the IPCC Data Distribution Center and the Hadley Center for Climate Prediction and Research, are then systematically examined. It follows that the above EASM weakening is not closely related to synchro-nizing anthropogenic global warming, and, therefore, it should be qualitatively natural change process. Over the 21st century, the EASM intensity is likely increased slightly by continually intensified greenhouse effect relative to the late 20th century.

Based on the long-term Central-north China precipitation (CNCP) time series reconstructed from the Qing Dynasty Official Document, the relationship between

CNCP and the Antarctic Atmospheric Oscillation (AAO) in June-July is examined. The analysis yields a (significant) negative correlation of 0.22. The signal of AAO in CNCP is further studied through analyses of the atmospheric general circulation variability related to AAO. It follows that AAO-related variability of convergence and convection over the tropical western Pacific can exert impact on the circulation condition and precipitation in north China (actually, the precipitation in the Yangtze River Valley as well) through atmospheric teleconnection known as the East Asia-Pacific (or Pacific–Japan) teleconnection wave pattern. There is also an AAO-connected wave train in the vorticity field at high troposphere over Eurasia, providing an anti-cyclonic circulation in central-north China favorable to the decline of precipitation in positive phase of AAO.

In this paper, the temporal variation characteristics of the dust storm in North China are investigated. Based on power spectrum analysis and wavelet analysis, 1956－1970 and 1985－1999 are chosen as the high-frequency and low-frequency dust storm decades respectively. Analysis results clearly show that the spring and wintertime anomalous atmospheric circulation between these two dec-ades are significantly different. Compared with the former decade, there are a strengthened polar vortex, enhanced westerlies near 50°N, and a weak East Asian major though in the winter of the latter decade. The north and center parts of the Siberian high and the Aleutian low become weak. The southerly and easterly wind anomalies appear over the north and east parts of China, which implies the weakening of East Asian winter monsoon. Meanwhile, northern China experiences warmer winters and wetter springs, which are in favor of the weakening of dust storm intensity in North China. There are significant out-of-phase relationships between dust frequency and wintertime westerly intensity, as well as between dust frequency and Arctic Oscillation. It is also found that the frequency of dust weather is strongly re-lated to winter-springtime East Asian monsoon intensity.

A new climate simulation for the middle Pliocene (ca. 3 Ma BP) is performed by a

global grid-point atmospheric general circulation model developed at the Institute of

Atmospheric Physics (IAP AGCM) with boundary conditions provided by the U. S.

Geological Survey’s Pliocene Research, Interpretations, and Synoptic Mapping (PRISM)

group. It follows that warmer and slightly wetter conditions dominated at the middle

Pliocene with a globally annual mean surface temperature increase of 2.60
C, and an

increase in precipitation of 4.0% relative to today. At the middle Pliocene, globally annual

terrestrial warming was 1.86
C, with stronger warming toward high latitudes. Annual

precipitation enhanced notably at high latitudes, with the augment reaching 33.5% (32.5%)

of the present value at 60–90
N (60–90
S). On the contrary, drier conditions were

registered over most parts at 0–30
N, especially in much of East Asia and the northern

tropical Pacific. In addition, both boreal summer and winter monsoon significantly

decreased in East Asia at the middle Pliocene. It is indicated that the IAPAGCM simulation

is generally consistent with the results from other atmospheric models and agrees well with

available paleoclimatic reconstructions in East Asia. Additionally, it is further revealed

that the PRISM warmer sea surface temperature and reduced sea ice extent are main factors

determining the middle Pliocene climate. The simulated climatic responses arising from the

PRISM reconstructed vegetation and continental ice sheet cannot be neglected on a

regional scale at mid to high latitudes (like over Greenland and the Qinghai-Tibetan

Plateau, and around the circum-Antarctic) but have little influence on global climate.

A new element tracer technique has firstly been established to estimate the contri-butions of mineral aerosols from both inside and outside Beijing. The ratio of Mg/Al in aerosol is a feasible element tracer to distinguish between the sources of inside and outside Beijing. Mineral aerosol, inorganic pollution aerosol mainly as sulfate and nitrate, and organic aerosol are the major components of airborne particulates in Beijing, of which mineral aerosol accounted for 32%―67% of total suspended particles (TSP), 10%―70% of fine particles (PM2.5), and as high as 74% and 90% of TSP and PM2.5, respectively, in dust storm. The sources from outside Beijing contributed 62% (38%―86%) of the total mineral aerosols in TSP, 69% (52%―90%) in PM10, and 76% (59%―93%) in PM2.5 in spring, and 69% (52%―83%), 79% (52%―93%), and 45% (7%―79%) in TSP, PM10, and PM2.5, respectively, in winter, while only ~20% in summer and autumn. The sources from outside Beijing contributed as high as 97% during dust storm and were the dominant source of airborne particulates in Beijing. The contributions from outside Bei-jing in spring and winter are higher than those in summer, indicating clearly that it was related to the various meteorological factors.

A nested regional meteorology/dust-transport model was applied to an Asian region including the

Taklimakan Desert. A three-grid system with a resolution of 81 km, 27 km and 9 km was designed and

model calculation was conducted over the whole period of April 2001 to examine the typical springtime

meteorology and some dust episodes over the Taklimakan Desert region. The performance model was

examined based on meteorological observation at WMO SYNOP station surrounding the Taklimakan

Desert and ADEC special observation site at Qira. The model results reproduced complicated airflows

within the Tarim Basin, strong down slope winds from the Tianshan Mountains when meteorological

disturbances crosses over the Taklimakan region, and a strong easterly flow from the Hexi Corridor side.

Composite analysis when the Tazhong site simulated an easterly wind was conducted and showed that

the percentage of the occurrence of this condition was approximately 50% of the full simulation period.

The scale of the easterly wind zone is 400 km in the Y direction, 1000 km in the X direction and 2–3 km

vertically. Simulated high dust concentration shows a good correlation with this easterly wind zone. The

model’s averaged dust concentration fields showed that the surface concentration ratio was approximately

0.6 between the eastern and western side of the Tarim Basin. However, the modeled ratio

showed an opposite relation with the SYNOP visibility, thereby indicating that the current high wind

type dust emission scheme may be insufficient to simulate the suspended dust phenomena in the western

part of the Tarim Basin.

Aerosol particle samples collected in spring 2002 in Beijing were analyzed to

investigate the impact of transport pathways on chemical composition of Asian dust

storms (DSs). The dust storms were divided into two episodes (i.e., DS I and DS II), which

were transported along different pathways identified by back-trajectory and PM10

concentrations. The transport pathway from the westerly direction could be seen as the

‘‘polluted’’ pathway and the north-northwesterly direction as the relatively ‘‘less-polluted’’

one. Dust storms not only delivered large amounts of mineral elements but also

carried significant quantities of pollutants. The source regions and transport pathways

were two vital factors affecting chemical composition of dust storms. Ca/Al could be used

as elemental tracer to identify the sources of Asian dust storms owing to the difference in

Ca content in different source regions. DS I of the ‘‘polluted’’ pathway carried more

pollution elements than DS II of the ‘‘less-polluted’’ one, and the pollution elements were

either from dust soil (such as Zn), the mixing of dust soil with pollution aerosol on the

pathway (such as As and Pb in DS I), the ‘‘pollution’’ dust resuspended on the pathway

and Beijing local area (such as S in DS I, As and Pb in DS II), or the reactions on the

surface of dust particles.

This paper uses a Modified Soil-Plant-Atmosphere Scheme (MSPAS) to study the interaction between land surface and atmospheric boundary layer processes. The scheme is composed of two main parts: atmospheric boundary layer processes and land surface processes. Compared with SiB and BATS, which are famous for their detailed parameterizations of physical variables, this simplified model is more convenient and saves much more computation time. Though simple, the feasibility of the model is well proved in this paper. The numerical simulation results from MSPAS show good agreement with reality. The scheme is used to obtain reasonable simulations for diurnal variations of heat balance, potential temperature of boundary layer, and wind field, and spatial distributions of temperature, specific humidity, vertical velocity, turbulence kinetic energy, and turbulence exchange coefficient over desert and oasis. In addition, MSPAS is used to simulate the interaction between desert and oasis at night, and again it obtains reasonable results. This indicates that MSPAS can be used to study the interaction between land surface processes and the atmospheric boundary layer over various underlying surfaces and can be extended for regional climate and numerical weather prediction study.

A series of sensitivity tests are performed to test the stability and sensibility of the Modified Soil-Plant-Atmosphere Scheme (MSPAS), which was wholly introduced in a previous paper. The numerical simulation results from the experiments show good agreement with physical reality. Besides, some of the results are illuminating. Together with the first paper, it is concluded that MSPAS is a simple but effective model, and it is practically valuable in the research work of desertification control and reforestation in China.

Both the observed background circulation and the northwest Atlantic sea surface temperature anomalies (SSTA) associated with the circulation anomaly over the Ural Mountains during early winter (October–December) are investigated, and it is shown that a positive height anomaly over the Urals is remotely linked to a positive SSTA by an upper wave-train-like anomaly chain across the North Atlantic and coastal Europe. To investigate whether and how the SSTA affects the circulation over the Urals,large-ensemble atmospheric general circulation model (GCM) experiments are conducted, and the results show that the SSTA forces a similar wave-train-like anomaly chain, resulting in a positive geopotential height anomaly over the Urals.

The mechanism that maintains the response is diagnosed by investigating the roles of anomalous diabatic heating, and transient vorticity forcing, via a linear baroclinic model (LBM). The results suggest that the two upstream anomalies in the chain are largely maintained by anomalous transient vorticity forcing, although it is modulated by anomalous diabatic heating. In contrast, the Ural response is largely maintained by anomalous diabatic heating. To mimic the initial mechanism of the response, an idealized heating representing the initial SSTA-induced heating is prescribed. The LBM response to the idealized heating is obtained, and then transient feedback to the heating-induced anomalous flow is simulated, via a linear storm track model (STM). The LBM responses to the anomalous transient vorticity forcing resulting

from the idealized heating resembles the GCM simulation upstream, but is not significant over

the Urals. This suggests further that the Ural response is triggered, and maintained, by anomalous diabatic heating.

The linkage between the Antarctic Oscillation (AAO) to the dust weather frequency (DWF) in North China is addressed. Here DWF denotes the number of days of dust weather events including dust haze, blowing dust and dust storm in one year. It is found that the interannual variation of AAO plays a significant role in the dust-related atmospheric circulation during boreal spring. AAO and DWF correlate well, with positive AAO tending to decrease DWF in North China. Two possible mechanisms for the AAO-DWF coupling are identified, one is related to a meridional teleconnection pattern; the other is related to a regional circulation pattern over the Pacific Ocean.

Based on the reanalysis data from NCEP/NCAR and other observational data, interannual variability of the Mascarene high (MH) and Australian high (AH) during boreal summer from 1970 to 1999 is examined. It is shown that interannual variability of MH is dominated by the Antarctic oscillation (AAO), and MH tends to be intensified with the development of the circumpolar lows in high southern latitudes. On the other hand, AH is correlated with AAO as well as El Nino and Southern Oscillation (ENSO), and tends to be intensified when El Nino occurs.

Since AH, especially MH, is positively correlated with AAO, composite analysis on the difference between the positive and negative MH is performed to reveal the physical mechanism responsible for the East Asian summer monsoon anomalies associated with AAO. The result shows that, with the intensification of MH, the Somali jet, and Indian monsoon westerlies, tend to be strengthened. Accordingly, AH and the associated cross-equatorial flow, become stronger whereas the trade wind over the tropical western and middle Pacific become weaker. In association with the above changes, convective activities near the Philippine Sea are largely suppressed, as a consequence, exciting a negative convection anomaly, and a Rossby wave train from East Asia via the North Pacific to the western coast of North America (a negative Pacific-Japan pattern). Corresponding to the negative Pacific-Japan pattern, an anomalous rainfall pattern appears in East Asia.

Correlation analysis between AAO and sea level pressure, 500 hPa geopotential height further indicates that AAO is a strong signal influencing the climate anomaly in both hemispheres, including East Asia. Due to the seasonal persistence, AAO and the related MH and AH in boreal spring, may provide some useful information for the East Asian summer monsoon prediction. With the intensification of MH during boreal spring through summer, the Meiyu/Baiu rainfall from the Yangtze River valley to the Japan Islands tends to increase, while less rainfall is found outside of this region. In contrast with MH, the effect of AH on summer rainfall is confined to southern China.

Aiming at the future development，the authors analyzed the present situation of the atmospheric science．Based on the an alysis，the strategy and the main tasks of the future research in China are proposed．The authors also an alyzed the existing problems in the atmospheric research in China and provide some suggestions for the policy makers.

Dust storms that occurred in East Asia during the spring of 2002 and

2003 were simulated by a regional dust deflation and transport model. Particular

focus was placed on dust incursion events over Taiwan. Two of the

events were analyzed in detail to give a complete picture of the three dimensional

transport patterns. The general characteristics of dust incursion

events were summarized, including the source locations, transport route

and distribution pattern in three dimensions, traveling time, duration of

incursion, and the seasonal spatial distribution of dust concentration. Significant

differences were also found in these characteristics between the

two years, the main cause of which was a change in regional climate patterns.

The performance of the model developed for this study was evaluated against

other dust forecast models, and found to have superior capability for forecasting

in the Taiwan area.

A numerical simulation of a sea-breeze front (SBF) is carried out to investigate the nocturnal frontogenesis

(FG) phenomenon that occurs as the SBF propagates inland during the nighttime. At first,

we reproduce the FG event of the nighttime SBF based on high-resolution numerical modeling. Then,

to reveal its formation mechanism, the FG equation is used, and contributions of each term in the FG

equation are estimated for explaining this nocturnal FG event. The results show that the nocturnal FG

event of the nighttime SBF: (1) is mostly attributed to the confluence effect due to the horizontal velocity

convergence and intensification of the horizontal potential temperature gradient at the front; (2) is

partly attributed to the no significant tendency of the turbulence effect associated with the surface

cooling.

Aerosolsampl es of PM2.5 and PM10 were collected in both summer and winter seasons from 2002 to 2003

synchronously at a traffic site, an industrial site, and a residential site in Beijing, which could basically be the

representatives over Beijing. Twenty-three elements and 15 ions together with organic carbon and elemental carbon

were analyzed systematically for characterization of Beijing aerosol. PM2.5 was the major part of the inhalable particles

(PM10), as the ratios of PM2.5/PM10 were 0.45–0.48 in summer and 0.52–0.73 in winter. SO4 2
, NO3
, NH4

+, organic

matter, crustal matter, and element carbon were the six dominant species, which totally accounted for 85.8–97.7% of

PM2.5. Secondary aerosol(SO 4

2
, NO3
, and NH4

+), road dust or/and long-range transported dust from outside Beijing,

industry and motor vehicles emission, coal burning were the major contributors to the air-borne particulate pollution in

Beijing. Overall, coal burning and the traffic exhausts, plus the dust from the long-range transport, could be the major

sources of the aerosol pollution at Beijing. A relatively even spatial distribution of chemical species in PM2.5 was found

while in PM10 a significant variation with the highest concentrations at the industrialsite in summer and at the

residentialsite in winter was observed. The concentrations of PM10, PM2.5 as well as various chemical species were

higher in winter than in summer. The contributions of mineralaerosolfrom outside Beijing were first estimated with a

newly developed element tracer technique, which accounted for 79% and 37% of the total mineral in PM10 and PM2.5

in winter, and 19% and 20% in summer, respectively. During the dust storm period from 20 to 22 March, it reached up

to 97% in TSP, 79% in PM10 and 76% in PM2.5. This is the technique, firstly, developed for estimating the relative

contributions of sources from inside and outside Beijing to the totalmineralaerosoland it could provide the basic

information in controlling the air-borne particulate pollution at Beijing.

r 2004 Elsevier Ltd. All rights reserved.

The regional-scale aerosol transport model Chemical Weather Forecasting System

(CFORS) is used for analysis of large-scale dust phenomena during the Asian Pacific

Regional Characterization Experiment (ACE-Asia) intensive observation. Dust modeling

results are examined with the surface weather reports, satellite-derived dust index

(Total Ozone Mapping Spectrometer (TOMS) Aerosol Index (AI)), Mie-scattering lidar

observation, and surface aerosol observations. The CFORS dust results are shown to

accurately reproduce many of the important observed features. Model analysis shows

that the simulated dust vertical loading correlates well with TOMS AI and that the dust

loading is transported with the meandering of the synoptic-scale temperature field at the

500-hPa level. Quantitative examination of aerosol optical depth shows that model

predictions are within 20% difference of the lidar observations for the major dust episodes.

The structure of the ACE-Asia Perfect Dust Storm, which occurred in early April, is

clarified with the help of the CFORS model analysis. This storm consisted of two

boundary layer components and one elevated dust (>6-km height) feature (resulting from

the movement of two large low-pressure systems). Time variation of the CFORS dust

fields shows the correct onset timing of the elevated dust for each observation site, but

the model results tend to overpredict dust concentrations at lower latitude sites. The

horizontal transport flux at 130
E longitude is examined, and the overall dust transport

flux at 130
E during March–April is evaluated to be 55 Tg.

On the basis of the recently estimated emission inventory for East Asia with a resolution of 1
11, the transport and

chemicaltransformation of sulfur compounds over East Asia during the period of 22 February through 4 May 2001 was

investigated by using the Models-3 Community Multi-scale Air Quality (CMAQ) modeling system with meteorological

fields calculated by the regional atmospheric modeling system (RAMS). For evaluating the model performance

simulated concentrations of sulfur dioxide (SO2) and aerosolsul fate (SO4 2 ) were compared with the observations on

the ground level at four remote sites in Japan and on board aircraft and vessel during the transport and chemical

evolution over the Pacific and Asian Pacific regional aerosol characterization experiment field campaigns, and it was

found that the modelreproduces many of the important features in the observations, including horizontal and vertical

gradients. The SO2 and SO4 2  concentrations show pronounced variations in time and space, with SO2 and SO4 2 

behaving differently due to the interplay of chemical conversion, removal and transport processes. Analysis of model

results shows that emission was the dominant term in regulating the SO2 spatialdistribution, while conversion of SO2 to

SO4 2  in the gas phase and the aqueous phase and wet removal were the primary factors that controlled SO4 2  amounts.

The gas phase and the aqueous phase have the same importance in oxidizing SO2, and about 42% sulfur compounds

(25% in SO2) emitted in the modeldomain was transported out, while about 57% (35% by wet removalprocesses)

was deposited in the domain during the study period.

r 2004 Elsevier Ltd. All rights reserved.

The seasonal variation of boundary layer ozone over

East Asia is investigated using a regional scale chemical

transport model, with the initial and boundary conditions of

chemical species obtained from a global chemistry model.

Comparisons with observations indicate that the model

reproduces the main daily and seasonal features of ozone

over eastern Asia. The seasonal variation of ozone has a

summer maximum and winter minimum at Waliguan station

(on the northeastern edge of the Tibetan Plateau), rather

than the spring maximum and summer minimum seen at

many other observational sites in the East Asian Pacific rim

region. Model results suggest that there is band of a high

ozone between 35
N
45
N from the western boundary

(70
E) to 130
E in the summertime. It is concluded that the

seasonal transitions associated with the Asian monsoon

system and transport from eastern/central China, Central/

South Asia and even Europe are significantly responsible

for the distinct ozone seasonal cycle at Waliguan. INDEX

TERMS: 0343 Atmospheric Composition and Structure: Planetary

atmospheres (5405, 5407, 5409, 5704, 5705, 5707); 0365

Atmospheric Composition and Structure: Troposphere—

composition and chemistry; 0368 Atmospheric Composition and

Structure: Troposphere—constituent transport and chemistry.

Citation: Zhu, B., H. Akimoto, Z. Wang, K. Sudo, J. Tang,

and I. Uno (2004), Why does surface ozone peak in summertime

at Waliguan?, Geophys. Res. Lett., 31, L17104, doi:10.1029/

2004GL020609.

The sea-surface temperature (SST) tripole, with warm anomalies off the east coast of the United States and cold anomalies north of 40N and south of 25
N, is the leading mode of interannual variability in wintertime North Atlantic SST. Its influence on

northwest African rainfall is investigated by using a large-ensemble of GCM simulations. Firstly the modeled basin-scale rainfall impact is displayed, and the results suggest: in early-mid winter (November–January), a positive SST tripole causes a

reduced rainfall extending from the tropical North Atlantic northeastward to Mediterranean while a negative SST causes a south-north increased rainfall across the central Atlantic from the subtropics to the midlatitude. In late winter (February–April) a

positive SST tripole causes a reduced rainfall in the central Atlantic from the subtropics to the midlatitude while a negative SST tripole induces a zonal increased rainfall from the subtropics to Mediterranean. The asymmetry and seasonal dependence of the SST influence on the basin-scale rainfall is consistent with the nonlinear response of the largescale atmospheric circulation. Under the large-scale impact background, northwest Africa regional rainfall response is also nonlinear and seasonally dependent. In early-mid winter a positive SST tripole causes reduced rainfall, while a negative SST has little effect. In late winter a negative SST tripole induces increased rainfall, while a positive tripole has little effect. A similarly large-scale asymmetric association between SST and rainfall circulation exists in observations in late winter, while the observed seasonal dependence of this association is relatively weak. Also, a similar SST tripole association with the regional rainfall over the northwest coast of Africa exists in observations.

The response of an atmospheric general circulation model (GCM) to the North Atlantic SST tripole exhibits

both symmetric and asymmetric components with respect to the sign of the SST anomaly. The symmetric part

of the response is characterized by a North Atlantic Oscillation (NAO)–like dipole with an equivalent barotropic

structure over the Atlantic. The asymmetry is manifested in a weaker and smaller-scale dipole response to the

positive SST tripole in contrast to a stronger and more zonally elongated dipole response to the negative tripole.

Mechanisms for developing and maintaining these GCM responses are elucidated through diagnostic experiments

using a linear baroclinic model and a statistical storm track model based on GCM intrinsic variability.

The NAO-like symmetric response is primarily maintained by a dipolar anomalous eddy forcing that results

from interactions between the heating-forced anomalous flow and the Atlantic storm track, as expected from an

eddy-feedback mechanism. To account for the asymmetry of the responses about the sign of the SST tripole, a

nonlinear eddy-feedback mechanism is proposed that extends the previous mechanism to include the nonlinear

self-interaction of the heating-forced anomalous flow and its effects on transient eddy feedbacks. The results of

idealized model experiments demonstrate that, due to its nonlinear self-interaction, the tripole heating induces

a much weaker response in the positive phase than in the negative phase. Interactions of these nonlinear heatingforced

anomalous flows with the Atlantic storm track result in asymmetric eddy vorticity forcings that in turn

sustain asymmetric eddy-forced anomalous flows in the two cases.

With the boundary conditions appropriate for the Last Glacial Maximum (LGM), including ice sheets, sea surface temperatures, sea-ice distribution, atmospheric CO2 concentration, the Earth’s orbital parameters, topography, and coastline, the atmospheric general circulation model of the Institute of Atmospheric Physics (IAP-AGCM) computes colder and drier conditions than for present day. Global annual-average surface temperature decreased by 5.3°C, and terrestrial precipitation was down by 29%. It is shown that IAP-AGCM LGM simulation compares favorably to results from other AGCMs, and/but generally shows a weak terrestrial cooling when compared to paleoclimatic reconstructions in tropics. The 21 ka (ka: thousands of years ago) vegetation reconstruction is introduced into the model to study the regional climate response to the changes in vegetation and associated soil characteristics over China. The additional cooling due to these two changes reduces, to a certain degree, the model-data discrepancies. In addition, under the precondition of continental ice existing over part of the Tibetan Plateau at the LGM, the authors examine the regional climate response to the continental ice. It follows that the glacial-age environment over the Tibetan Plateau is a very important factor for 21 ka climate simulation in East Asia.

The monthly reanalysis data set and the analyzed precipitation data set are used to study the interannual variability of Somali Jet (SMJ) and its influences on the interhemispheric water vapor transport and on the East Asian summer climate.

It is indicated that SMJ plays a key role in the water vapor transport between the two hemispheres. SMJ transports water vapor through the equator from the southern hemisphere to the northern hemisphere during boreal summer time, and from northern hemisphere to the southern hemisphere during boreal winter time.

The interannual variation of SMJ is found to be linked with the many changes around the globe, including the wave pattern along East Asia coast, the South Asian high, and dipole pattern to the southeast of Australia. The results also reveal that interannual variation of SMJ at boreal spring has significant influences on the East Asian summer rainfall and atmospheric circulation. Since the changes of SMJ precede the changes of East Asian summer climate, these findings may help to improve the summer climate prediction in East Asia.

Features of an extra-strong warm winter event in North Asia in 2002 and its accompanying anomalous atmospheric circulation were studied through diagnosis on the atmospheric reanalysis data set. Results show that the winter of 2002 is of the warmest in the recent 54 years in North Asia, which was caused by both decadal scale and interannual scale variability. The interannual variability is proved to be as the main cause for the event, and it is related to the global scale atmospheric circulation anomalies, with the strongest of them in the Eastern Hemisphere and in the middle and high latitude region of the Southern Hemisphere.

　This paper reports the first GCM - based prediction experiment results on the winter climate and spring dust climate several months ahead of the time. The ensemble prediction shows that the forthcoming winter will have normal precipitation in the North and slightly more precipitation in the South, and normal temperature in the countrywide. Therefore, it will not be the warm winter in China. In comparison, the

North Eurasia will have a warm winter. Precipitation will be normal in Northwest , Central North, and Northeast in the next spring, and other parts will have a little more precipitation. The temperature will be normal in most areas. In accordance, North China will face normal, instead of stronger, dust storm occurrence. However, due to the recent enhancement tendency, strong dust storm occurrence will be still possible.

Using the nine-level Atmospheric General CirculationModel developed at the Institute of Atmospheric Physics (IAP9L-AGCM) under the Chinese Academy of Sciences, 30-year extraseasonal short-term ensemble hincast of winter climate is performed, with integrations starting from annual autumn during 1969-1998. Winter climate predictability over China is then evaluated for the first time. It follows that the predictability is higher in tropics than in extratropics.

Also, it is higher over ocean compared with land, especially for surface air temperature. With height increasing in troposphere, the predictability of geopotential height slightly changes zonally, but for weakening of band-ship distribution and dropping near the date line. Of all analyzed variables, the prediction skill of air temperature and geopotential height (precipitation) is the highest (smallest).

In addition, the predictability of winter climate over China and even East Asia enhances obviously during ENSO cycle, especially during La Niña phase. Simulation comparison against verifying analysis for surface temperature anomaly exhibits the model’s skill in predicting surface temperature’s interannual variation trend in winter.

Features of an extra-strong warm winter event

in North Asia in 2002 and its accompanying anomalous atmospheric circulation were studied through diagnosis on the atmospheric reanalysis data set. Results show that the winter of 2002 is of the warmest in the recent 54 years in North Asia,

which was caused by both decadal scale and interannual scale variability. The interannual variability is proved to be as the main cause for the event, and it is related to the global

scale atmospheric circulation anomalies, with the strongest of them in the Eastern Hemisphere and in the middle and high latitude region of the Southern Hemisphere.

In this paper, the authors define the spring monsoon in South China, and study the climatology and the interannual variation through analysis of the precipitation and the related atmospheric circulation, as revealed by the NCEP/NCAR reanalysis data. The results indicate that the spring monsoon season in South China occurs climatologically in April and May, which is supported by both seasonal and interannual variation of the atmospheric circulation and precipitation. The related atmospheric circulation is different from that during the East Asian summer or winter monsoon season. The interannual variation of the spring monsoon rainfall in South China relates primarily to the anomalous circulation over the North Pacific, which is linked with the westerly jet over North Asia and with the polar vortex. It is also connected with sea surface temperature anomalies in the Pacific. Changes in the Asian tropical atmospheric circulation have little influence on the spring monsoon in South China according to this research.

The instability in the relation between the East Asian summer monsoon and the ENSO cycle in the long term variation is found through this research. By instability, we mean that high inter relation exists in some periods but low inter relation may appear in some other periods. It is reveals that the interannual variation of the summer atmospheric circulation during the ‘high correlation’ periods (HCP) is significantly different from that during the ‘low correlation’ periods (LCP). Larger interannual variability is found during HCP for trade wind over the tropical eastern Pacific of the Southern Hemisphere, the low—level air temperature over the tropical Pacific, the subtropical high pressure systems in the two hemispheres, and so on. The correlation between summer rainfall over China and ENSO is as well different between HCP and LCP.

Acid rain and its neutralization by yellow sand in East Asia were investigated numerically by an Air Quality Prediction Modeling System (AQPMS). AQPMS consists of advection, diffusion, dry and wet deposition, gas-phase chemistry and the liquid-phase chemistry. A new deflation module of the yellow sand (Asian soil dust) was designed to provide explicit information on the dust loading. Different from the previous ones for Sahara and Australian deserts, this new one includes three major predictors, i.e., the friction velocity, the surface humidity and the predominant weather system, while this module was linked to the AQPMS. For model validation, the predicted pH values and sulfate- and nitrate-ion levels of precipitation, together with the surface concentrations of gaseous pollutants, were compared with the measured values at atmospheric monitoring stations, and a reasonable agreement was obtained. Firstly, the trend of the acid rain in East Asia due to the rapid increase of Chinese pollutants emission was investigated, and a remarkably rapid increase of acid rain area was predicted in the period from 1985 to 1995, the monthly mean pH values showing the decrease of 0.3–0.8 in the area from the center to northeast in China, and 0.1–0.2 even in Japan and Korea. Secondly, the simulation results of April 1995 exhibited a strong neutralization of the precipitation by the yellow sand. The monthly mean pH values in the northern China showed a remarkable increase of 0.6–1.8 by neutralization effect of the yellow sand, while the increases in the southern China were less than 0.1. Even in Korea and Japan the yellow sand caused the increase of the pH value of rain by 0.1–0.2.

Simulations of monthly mean nitrate concentrations in precipitation over East Asia

Atmospheric Environment, Volume 36, Issue 26, September 2002, Pages 4159-4171

Junling An, Hiromasa Ueda, Zifa Wang, Kazuhide Matsuda, Mizuo Kajino and Xinjin Cheng

A comprehensive Air Quality Prediction Modeling System is applied to simulate the

pH values in precipitation and to investigate neutralization by soil aerosols and their

influence on the distribution of acid rain over east Asia. A modified deflation module is

designed to provide explicit information on the soil aerosol loading. Numerical simulation

was performed for 1 year, from 15 December 1998 to 31 December 1999. Wet deposition

monitoring data at 17 sites of the Acid Deposition Monitoring Network in east Asia in

addition to State Environmental Protection Agency data were used to evaluate the model,

and a reasonable agreement was obtained. Observed evidence clearly shows that in

northern China acid deposition is heavily influenced and buffered by natural soil dust from

desert and semiarid areas. The observed mean rainwater pH value in northern China is the

highest, between 6.0 and 7.2, while in southern China, where many areas severely

impacted by acid precipitation are located, the pH value is much lower, between 3.5 and 5.

In Japan the mean pH value is 4.7, significantly higher than that in southern China, while

in South Korea the pH value is intermediate between those in northern China and Japan.

The model is capable of reproducing this geographical distribution of rainwater pH over

east Asia. The simulation results for 1999 demonstrated strong neutralization of

precipitation by soil aerosols over northeast Asia, and the distribution pattern of acid rain

was also altered. The annual mean pH values in northern China and Korea show a

remarkable increase of 0.8–2.5, while the increase in mean pH values over southern China

and Japan are less than 0.1. The neutralization effects vary by season, with the greatest

influence in spring, when pH values increased by 0.1–0.4 in Japan, 0.5–1.5 in Korea, and

more than 2 in northern China.

The tropical heating and transient activity features

during the period of the persistent anomaly of summertime circulation over the Ural Mountains are studied,and a possible mechanism responsible for formation and maintenance of persistent anomalies is proposed. The mechanism can be summarized as a kind of self-sustaining through a two-way interaction of stationary wave with transient eddies under the consistent forcing of abnormal heating in the tropics.

The transition of the global atmospheric circulation in the end of 1970’s can clearly be detected in the atmospheric temperature, wind velocity, and so on. Wavelet analysis reveals that the temporal scale of this change is large than 20 years. Studies in this work indicate that the trend of the transition over the mid-latitude Asia is opposite to that of global average for some variables at the middle troposphere. Another finding of this research is that the African-Asian monsoon circulation is weaker and the trade wind over the tropical eastern Pacific is weaker as well after this transition. Such a signal may be found in the summer precipitation over China as well.

The atmospheric intraseasonal oscillation(ISO) and its interannual variability are simulated by the atmospheric circulation mode, which was developed at the Institute of Atmospheric Physics. Two numerical experiments were performed, corresponding to the AMIP-I and AMIP-II simulations, respectively. The model reasonable reproduces the majao aspects of the ontraseasonal oscillation, including the propagating property and the seasonal differences in the tropics, the wavenumber structure of ISO in the globe,and the globle coincidence in the interannual variation of ISO. Comparison of the results between the two experiments suggests that improvement of the boundary forcing or condifering the air-sea interaction may help to improve the simulation on the ISO and its interannual variability.

Based on a 200 year simulation and reanalysis data (1980 1996), the general characteristics of East Asian monsoon (EAM) were analyzed in the first part of the paper. It is clear from this re-search that the South Asian monsoon (SAM) defined by Webster and Yang (1992) is geographically and dynamically different from the East Asian monsoon (EAM). The region of the monsoon defined by Webster and Yang (1992) is located in the tropical region of Asia (40 110°E, 10 20°N), including the Indian monsoon and the Southeast Asian monsoon, while the EAM de-fined in this paper is located in the subtropical region of East Asia (110 125°E, 20 40°N). The components and the seasonal variations of the SAM and EAM are different and they characterize the tropical and subtropical Asian monsoon systems respectively. A suitable index (EAMI) for East Asian monsoon was then defined to describe the strength of EAM in this paper. In the second part of the paper, the interannual variability of EAM and its relationship with sea surface temperature (SST) in the 200 year simulation were studied by using the composite method, wavelet transformation, and the moving correlation coefficient method. The summer EAMI is negatively correlated with ENSO (El Nino and Southern Oscillation) cycle represented by the NINO3 sea surface temperature anomaly (SSTA) in the preceding April and January, while the winter EAM is closely correlated with the succeeding spring SST over the Pacific in the coupled model. The general differences of EAM between El Nino and La Nina cases were studied in the model through composite analysis. It was also revealed that the dominating time scales of EAM variability may change in the long-term variation and the strength may also change. The anoma-lous winter EAM may have some correlation with the succeeding summer EAM, but this relation-ship may disappear sometimes in the long-term climate variation. Such time-dependence was found in the relationship between EAM and SST in the long-term climate simulation as well.

An effective method was proposed for correcting the seasonal—interannual prediction of the summer climate anomaly. The predictive skill can be substantially improved by applying the method to the seasonal—interannual prediction carried out by a coupled ocean—atmosphere model. Thus the method has the potential to improve the operational summer climate predictions.

Based on the analysis of the sea surface temperature anom aly (SSTA) and the atmospheric general circulation for three flood years (1954, 1998, 1991) in China, it is revealed that the SSTA may not be the necessary condition for the flood in China.

Meanwhile, the anomaly of the atmospheric circulation over the high latitude Eurasia during spring is crucial to the summer monsoon circulation and precipitation over East Asia. Therefore, it is suggested that the study on the dynamics and variability of the atmospheric circulation over Eurasia should be enhanced.

The mid—Holocene climate about 6000 years ago was simulated by using the atmospheric general circulation model. The orbital parameters for 6 ka BP (before present) were prescribed and other forcing factors were set in the modern conditions. Results show that the large—scale climate change in the African—Asian monsoon areas during the summer—time is strongly compared to the present climate, while the changes in other seasons and regions are generally weak. The results also revealed the change of the low frequency oscillation in the atmosphere.

Sets of numerical hindcast experiments were carried out to study the excessive rain that happened over China in 1998 by using an atmospheric general circulation model. The monthly sea surface temperatures for 1998 were prescribed as the model boundary conditions. The initial atmospheric conditions for each of the 30 member simulations were obtained from the daily reanalysis data for 00 UTC from April 1 to April 30, 1998. The initial conditions for snow mass, soil temperature, and soil wetness were prescribed as those of the model climatology.

The ensemble averages of the 30 member hindcast experiments captured the positive rainfall anomaly occurred over China in the summer of 1998, with 5 degree of northward shift. The observed patterns of summer geopotential anomalies were qualitatively reproduced as well. It was revealed that initial atmospheric anomalies in April have apparent impacts on the simulated flow patterns over Eurasia and the North Pacific, and rainfall anomalies over China during the summer of 1998. However, the overall results suggest that tropical sea surface temperature anomaly played a key role in heavy rainfall over China in 1998.

A deflation module of soil and sand dust loading,especially for Asian dust(called yellow sand or Kosa),has been designed to provide explicit information on emission intensity for use in modeling long-range transport of yellow sand over East Asia.In contrast to previous modules for Sahara and Australian deserts, it includes three major predictors,the friction velocity,the surface humidity,and the dominant weather system.Comparison of the deflation module results,using these three parameters together or separately,with observed data on dust deflation in April and july 1988,shwos that the best estimate can be obtained by considering the three predictors together when we take the minimum of the total error ratio as the selection criteria.It indicates that last two predictors provide a limitation for deflation and can desreasse the number of false declarations from 23 to 7%,especially in the wet season.Aregional long-range transport model for Kosa is introduced,which considers various parameters such as particle size,transport,diffusion,and removal in detail.The model results show a reasonable agreement with the observations during Kosa episodes in April 1988.A size-resolved analysis explains the peculiar multi layered vetrical distribution of dust at large distancel from the source areas;that is,for fine particles on peak appears close to the ground,while the other is in the middle troposphere.

An air pollution perdiction model system (APOPS)is developed and applied to northern Taiwan with complex terrain and local thermal circulations,It consists of a nonhydrostatic mesoscale meteoro-logical model system(MMPMS)and a gas/aerosol transport and air quality model(GATAM),The basic processes relevant to modeling the urban air pollution problems such asmeteorology,dispersion,chemistry and deposition are solved at the same timc on practically the same grid.The APOPS was tested on a high-ozone event in northern Taiwan on 16 November 1998 Comparison with observed surface winds shows able to predict local flow patterns such as sea/land breezes and mountain-valley wind in this high air pollution episode.The predicted surface concentrations of ozone and other pollutants are compared with measured values,and a fairly good agreement with the mean normalized biases of -6%,-11%,forone-day simulation and for daytime ,respectively,is obtained for ozone Thus,it is confirmed that the APOPS can be utilized to predict urban air quality in complex terrain area.

El Nin˜o and the related phenomenon Southern Oscillation (ENSO) is the strongest signal in the interannual variation of ocean-atmosphere system. It is mainly a tropical event but its impact is global. ENSO has been drawing great scientific attention in many international research programs. There has been an observational system for the tropical ocean, and scientists have known the climatologies of the upper ocean, developed some theories about the ENSO cycle, and established coupled ocean-atmosphere models to give encouraging predictions of ENSO for a 1-year lead. However, questions remain about the physical mechanisms for the ENSO cycle and its irregularity, ENSO-monsoon interactions, long-term variation of ENSO, and increasing the predictive skill of ENSO and its related climate variations.

There was significant difference between vegetation cover in mid-Holocene and that at present over China based on various evidences as concludes by Shi et al [1992]. These changes were introduced to the climate model to study the role of the changing vegetation and associated soil to the simulated climate of mid-Holocene at 6000 years before present (BP) with bigger seasonal cycle of insolation than present (caused by the change of orbital parameters). Results show that the changes in vegetation and soil could further strengthen the monsoon rainfall over China. We found that replacing the today’s seasonal cycle of insolation by that of mid-Holocene increases the summer (June-August) precipitation by 20% in eastern China (100-120E,18-42N); while considering both the effect of changing orbital forcing and the vegetation and soil, the total summer precipitation increase in 29% in the same region. Compared with the reconstructed precipitation over China, the results of that including changing vegetation and soil is quantitatively better.

Based on a set of systematic hindcast experiments by IAP and OSU AGCMs and theoratical analysis the uncertainty of short-term climate prediction were studied preliminarily. The paper stressed on the uncertainties induced by atmospheric internal dynamics. The conceptual model of short-term climate predictabililty were concluded and the preliminary dynamical mechanisms were analysed. Future suggestions of research wre proposed in the last.

The interannual variabilities of the climatological simulation (V1) and the AMIP (Atmospheric Model Intercomparison Project) simulation (V2) by the IAP 9-Level Atmospheric General Circulation Model are studied and discussed in this paper. Based on the analysis of ratio of variability (R) of above two simulations the predictability of the model on the interannual climate variation are studied as well. Results show that V2 is bigger than V1 generally and V2 is more comparable to the real variability of the atmosphere, the major difference of V1 and V2 is in the tropics, for temperature and geopotential height the predictability is higher in the tropics while in the extra-tropics there is almost no predictability and the predictability is bigger in higher level than in lower level. The predictability for precipitation is generally low in the globe, and generally the predictability is high in the tropical eastern Pacific for the lower level. This study suggests that the possible way of increasing the model predictability is the improvement of land surface process modelling and the inclusion of the interannual variations of the land surface conditions (snow cover, albedo, soil moisture, etc.) as the forcing factor for climate modelling and prediction.

A three-dimensional regional Eulerian model of sulfur deposition and transport is developed. Processes treated in the model include emission, transport, diffusion, gas-phase and aqueous-phase chemical process, dry deposition, rainout and washout or sulfur. A “looking up table” method is provided to deal with the gas-phase chemical process including sulfur transfer. Dry-depositon velocity considers the influence of underlying surface, wind, degree of stabil-ity by parameterization. Model calculated values reasonably agrees with observation. Distribution of sulfur deposi-tion and transport in East Asia are also analyzed in this paper. Some amount of sulfur emission of different countries transport across boundaries, but the main origin of sulfur deposition in each country in East Asia is from itself. Furthermore, some transport paths on different layers and outlet or inlet zones are found. According to sulfur bal?ance and budget we concluded that sulfur outlets are bigger than inlets across boundary and emissions are more than deposition in most places of East Asia.

A three dimensional regional Eulerian model of sulfur deposition and tranport has been developed. It includes emission, transport, diffusion, gas-phase and aqeous-phase chemical process, dry depostion, rainout and washout process. A looking up table method is provided to deal with the gas-phase chemical process including sulfur transfer. Calculated values have reasonable agreement with observations. Distribution of sulfur deposition and transport in East Asia are also analyzed in the paper. Simulation shows that sulfate (SO 4 2– ) is the main substance to transport in long range transport. Some amount of sulfur emission of different countries transport across boundaries, but the main origin of sulfur deposition in each country in East Asia is from herself. Furthermore, some transport paths on different layers and outlet or inlet zones are found.