2020年江淮流域超强梅雨年际异常的驱动因子分析

利用观测诊断和数值模拟相结合的方法，研究了2020年江淮流域6～7月超强梅雨年际异常的环流特征和驱动因子。结果表明:（1）2020年梅雨期长度和江淮流域总降水量均为1961年以来第一位，超强梅雨主要与西北太平洋异常反气旋（WNPAC）的异常偏强和异常西伸有关，WNPAC为江淮流域梅雨期持续的强降水提供了充沛的水汽来源；（2）2019年11月至2020年3月，赤道中东太平洋发生一次弱的中部型El Ni?o事件，本次事件持续时间短、强度偏弱，不足以激发和维持2020年梅雨期异常偏强的WNPAC，而春、夏季热带印度洋和热带北大西洋海温异常持续偏暖是WNPAC异常偏强和西伸的主要驱动因子；（3）热带印度洋暖海温在其东部的西太平洋激发出大气Kelvin波响应，造成了纬向风变化的不均匀分布，通过埃克曼抽吸，抑制了局地对流活动，驱动了WNPAC的生成；而热带北大西洋暖海温则引起局地对流活动增强，导致热带北大西洋上空上升运动和热带中部太平洋下沉运动增强，在西北太平洋上空激发异常的低空反气旋；热带印度洋和热带北大西洋暖海温对2020年6～7月WNPAC异常偏强均有显著的正贡献。

What Drives the Super Strong Precipitation over the Yangtze–Huaihe River Basin in the Meiyu Period of 2020?

During the Meiyu Period (June–July, JJ) of 2020, the Yangtze–Huaihe River basin (YHRB) in China experienced record-breaking rainfalls, resulting in severe floods and disasters. These rainfall anomalies were closely related to the extremely strong anomalous anticyclone developed over the western North Pacific (WNPAC), which favored convergence of water vapor over YHRB. The aim of this study is to determine the cause of the record-breaking rainfalls and WNPAC in the Meiyu period of 2020. It was found that a weak Central-Pacific El Ni?o rapidly decayed in spring and developed to a La Ni?a in late summer, whereas sea surface temperature (SST) in the tropical Indian Ocean (TIO) and tropical northern Atlantic (TNA) was considerably and persistently high from the previous winter to summer. The results showed that the weak decaying El Ni?o alone was insufficient to sustain the strong WNPAC in JJ of 2020, whereas the long-lasting warm SST anomalies in the TIO and TNA significantly contributed to the enhancement and westward shift of the WNPAC. The TIO warming intensifies the WNPAC by propagating Kelvin waves eastward and/or modulating the Hadley circulation. The TNA warming can force a westward-extending overturning circulation over the Pacific–Atlantic Oceans, with a sinking branch over the central tropical Pacific, which suppresses the convection activity over there and gives rise to the WNPAC. The TIO and TNA warming significantly contributed to the extremely strong WNPAC in JJ of 2020.