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夏季北极海冰对1998和2016年中国东部8月降水反向模态的影响

Effect of Summer Arctic Sea Ice on the Reverse August Precipitation Anomaly in Eastern China between 1998 and 2016

[2019-07-03]


【中文介绍】


1997/19982015/2016年爆发了两次超强厄尔尼诺事件,其强度相当,对应次年夏季也都体现为长江流域降水的一致偏多。然而在次季节尺度上,两次事件所对应的降水异常却存在很大的差别:19982016)年8月降水呈现为长江以南偏少(多),长江以北偏多(少)的偶极型模态(图1a1b)。由此引出一个科学问题:两次相似的超强厄尔尼诺事件之后,为何在次年8月,中国东部降水的异常却呈现近乎相反的空间分布?

南京信息工程大学的博士研究生沈海波,与中科院大气所、挪威卑尔根大学的贺圣平博士联合王会军院士,通过对观测数据的统计诊断以及数值试验的分析,发现中国东部8月降水异常的这种偶极型模态与夏季巴伦支-喀拉海的海冰变化存在紧密联系(图1c)。7月巴伦支-喀拉海的海冰异常会在欧亚大陆上激发出一条向东传播的罗斯贝波列,波动传播到东亚在急流的出口区产生平均流向扰动能量的转换,进而在8月引起径向的太平洋-日本遥相关,调制中国东部的环流及降水。

19982016)年夏季巴伦支-喀拉海的海冰偏多(偏少),可能是导致两年8月降水异常反向的原因之一。该文发表于Journal of Climate


【英文介绍】


1997/1998 and 2015/2016 El Niño episodes are regarded as two super El Niño events on record and have exerted profound influence on eastern China summer rainfall, as expected. However, on the sub-seasonal time scale, summer rainfall in these two years shows dramatic diversity, although the characteristics of the two super El Niño are similar. For instance, the rainfall increases (decreases) over central China (approximately 30°−35°N) and decreases (increases) over southeastern China (approximately south of 25°N) in August 1998 (2016) (Figure 1a and 1b). This raises a scientific question: why is the August precipitation anomaly over eastern China reverse under two similar super El Niño conditions?

Based on the observational and model simulated analysis, PhD student Haibo Shen (Nanjing University of Information Science & Technology) together with Dr. Shengping He (from Institute of Atmospheric Physics, Chinese Academy of Sciences and Geophysical Institute, University of Bergen) and Prof. Huijun Wang (Nanjing University of Information Science & Technology) identified a close connection between the summer sea ice variability over Barents-Kara Seas and the August precipitation anomaly over eastern China (Figure 1c). The sea ice area anomaly over the Barents-Kara Seas induces a Rossby wave propagating eastward to East Asia, which causes positive barotropic and baroclinic energy convection near the exit of the Asian jet stream. The accumulation of perturbation energy in East Asia stimulates the formation of the Pacific-Japan teleconnection, which is favorable for the dipole rainfall anomaly pattern over eastern China.

Thus, the positive and negative sea ice area anomaly over the Barents-Kara Seas in 1998 and 2016 may contribute the reverse August precipitation anomaly in eastern China.

The study was published in Journal of Climate.



                                


1. 1998(a)2016(b)8月份中国东部降水异常的空间分布(单位:mm/day);(c) 7月巴伦支-喀拉海的海冰面积指数与8月降水的相关系数(指数乘以-1,因此,负的相关系数对应海冰偏少)


Figure 1. Distribution of August precipitation anomalies (units: mm/day) in China east of 105°E during 1998 (a) and 2016 (b); (c) Correlation maps of the August precipitation anomaly with regard to the July sea ice area index during 1979–2016 (the index is inverted; i.e., the negative correlation coefficients correspond to precipitation anomalies associated with anomalously low sea ice area). Dotted regions indicate that the values are significant at the 90% confidence level, based on the Student’s t test.

 

【引用格式】


Shen, H., S. He, and H. Wang, 2019: Effect of Summer Arctic Sea Ice on the Reverse August Precipitation Anomaly in Eastern China between 1998 and 2016. J. Climate, 32, 3389–3407.   








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