【中文介绍】

自1979年以来，北极海冰快速减少，其气候效应受到广泛关注。以往的研究更多地集中在近几十年前期秋季海冰减少与北半球冬季气候的联系，但是其与夏季气候之间是否存在显著联系鲜有研究涉及。本研究揭示了秋季海冰和东亚夏季降水之间存在显著关联，并进一步探讨了这种跨季节尺度的联系发生的可能机制，可为延长东亚夏季降水预测时效提供新的科学依据。

本研究发现：秋季喀拉海-拉普捷夫海海冰面积偏少时，东北地区降水偏多、中国东部和日本以南降水偏少（“北多南少”）。这一联系仅在90年代后期以后变得显著：秋季海冰偏少时，同期海平面气压场表现为西伯利亚中部和中国东北地区上空的正、负异常中心，对应“西伯利亚中部降水偏少、东北地区降水偏多”的分布型，进而导致中西伯利亚土壤偏干。由于冷季中高纬地区的陆气相互作用非常弱，上述西伯利亚土壤偏干信号可从冬季持续到春季，到夏季这种异常信号通过陆气相互作用影响大尺度环流，引起东亚地区高度场北负南正的空间异常分布型，对应“北多南少”的降水格局。另一方面，秋季海冰偏少时，东北地区冬、春季积雪偏多，到夏季积雪融化可以通过改变陆气水热通量影响大气环流变化，产生“北多南少”的降水分布。数值模拟试验结果可从一定程度上再现上述秋季海冰与夏季环流之间的联系。

【英文介绍】

This study explored the interannual relationship between autumn Arctic sea ice concentration (SIC) and the subsequent summer precipitation over East Asia (EASP). Since the late-1990s, the declining SIC in the Kara-Laptev Seas has been significantly correlated with EASP as well as extremely positive anomalies in northern China and intensely negative anomalies in central-eastern East Asia. However, there was a weak correlation between autumn SIC and EASP before the late-1990s. Furthermore, the anomalous precipitation pattern in summer and its connection with autumn SIC variability can be explained by the seasonal persistence of continental processes (snow depth and soil moisture) into the spring. In particular, a decreasing SIC was connected with simultaneously positive and negative precipitation anomalies over northeastern China and the Siberian region, respectively, since the late-1990s and tends to produce corresponding soil moisture anomalies over the Eurasian continent. Declining SIC also favors increased snow depth anomalies in winter over northeastern East Asia. These anomalous signals of surface processes can persist from winter into the subsequent spring, making the connection between the autumn SIC and EASP possible. The Community Earth System Model Large Ensemble simulations further verified these physical processes. More detailed mechanism for this relationship needs to be stressed in further work by numerical simulations. The results have important implications for extending the seasonal prediction validity of EASP. Moreover, before the late-1990s, SIC-related circulation anomalies shifted westward and northward as negative precipitation anomalies developed over west Siberia in autumn. As a result, anomalous dry soil conditions in Siberia persisted into the subsequent spring and then led to wetter-than-normal conditions through locally negative soil moisture-precipitation feedback before the late-1990s.

                          图1. 秋季喀拉海-拉普捷夫海海冰与东亚夏季降水的奇异值分解第一模态空间分布及时间系数。

Fig. 1. First SVD mode of autumn SIC and subsequent summer precipitation for the period 1979/80−2016/17. (a) The spatial pattern of SVD1-SIC; (b) the spatial pattern of SVD1-precipitation; (c) the corresponding time series.

【引用格式】

Liu, Y., Zhu, Y., Wang, H., et al., 2019: Role of autumn Arctic Sea ice in the subsequent summer precipitation variability over East Asia. International Journal of Climatology, https://doi.org/10.1002/joc.6232.