海温异常对东亚夏季风影响机理的研究进展

利用湖北省梅雨监测资料、国家气候中心新百项指数和NCEP/NCAR环流资料，分析了2020年湖北梅雨异常特征及其成因。结果表明：（1）2020年湖北梅雨持续时间异常长，为54 d，仅次于1996年；梅雨量异常多、强度强、雨日率大，均为1961年以来第1位。（2）高空西风急流、副热带高压、夏季风系统的冬夏调整季节性进程早，是造成湖北入梅早的主要原因。西风急流和副热带高压在7月下旬北跳，较常年时间偏晚，导致了出梅晚。入梅早、出梅晚，梅雨持续时间异常长。（3）在前冬El Niño事件、春夏热带印度洋海温偏暖和北大西洋三极子负位相的共同影响下，欧亚中高纬经向环流发展，冷空气活跃，副热带高压强且位置稳定，西侧水汽输送强，冷暖气流在长江中下游交汇，造成湖北省梅雨量异常偏多。

The influence of ENSO on the summer climate change in China and its mechanism

By using Hubei Meiyu monitoring data, NCC new indices and NCEP/NCAR circulation reanalysis data, the characteristics and cause analysis of abnormal Meiyu over Hubei Province in 2020 are analyzed. (1) The results show that Meiyu in 2020 is abnormal with a longer duration and more precipitation. The duration is 54 days, only second to 1996. The anomalous characteristics of Meiyu in 2020 are more precipitation, strong intensity and rainy day rate, all taking the first place since 1961. (2) The early transitions of circulations from winter pattern to summer pattern, such as westerly jet, subtropical high and summer monsoon, result in the early onset of Meiyu. The late outset of Meiyu is induced by the late northward jump of the upper westerly jet and subtropical high in late July. Early onset and late outset lead to abnormal long duration of Meiyu in 2020. (3) The decay of El Niño event appears in the previous winter, while the persistent warming of the Indian Ocean basin-wide mode and negative phase of North Atlantic Triple index appear in spring and summer. With the background of such sea surface temperature anomalies, meridional circulation in mid- and high-latitude develops, resulting in active cold air. The subtropical high is strong and persists, and water vapor transport over its west side is strong too. The abnormally strong water vapor transport intersects with active cold air over the Lower Yangtze Region, resulting in abnormal precipitation of Hubei Meiyu.