2020年秋季我国气候异常特征及成因分析

Features and Possible Causes of Abnormal Climate over China in Autumn 2020

2020年秋季,我国气候总体呈现“暖湿”的特点,但是季节内变率很大,9月降水“南多北少”、10月降水“中间多南北少”,11月降水“北多南少”。环流特征显示,秋季欧亚中高纬度总体为“两脊一槽”型,季节内波动大;西太平洋副热带高压(以下简称副高)持续偏强、偏大,西伸明显,但脊线位置的季节内变化大,9月偏南,10月略偏北,11月明显偏北。外强迫信号影响分析显示,热带印度洋全区一致偏暖有利于副高持续偏强、偏大、偏西;而热带中东太平洋El Nino事件春季结束后于秋季进入La Nina状态的海温演变过程,对热带和副热带环流系统具有重要影响,有利于秋季(尤其是10月)副高偏北。9月降水“南多北少”的异常分布与南海区域对流活动偏弱、偏南导致的副高偏南有关。研究显示,海温外强迫演变以及热带对流活动季内变化的共同作用导致了2020年秋季降水呈现出季节内变率大的特征。

In autumn 2020,China’s climate presented the features of“warmer and wetter”than normal.But the intra-seasonal variability was significant.The distribution of precipitation anomaly shows rainfall was more than normal in south and less than normal in northern part of China in September,and the pattern was reversed in November.The circulation of mid-high latitudes of Eurasia in autumn was in the“+-+”EAP pattern,which also showed obvious intra-seasonal variability.The subtropical high over western Pacific(WPSH)continued to be stronger,larger and more westward,but developed southward to its climate state in September and northward in October-November.Further analysis proves that wide warming in the tropical Indian Ocean Basin was beneficial to the strong,large and westerly features of WPSH in autumn.The evolution of SST over tropical mid-east Pacific,where El Nino event ended in spring and La Nina started in autumn,had an important impact on tropical and subtropical circulations and favorable to the northward of WPSH,especially in October.Convective activity in the western Pacific warm pool was significantly weaker and more southward than normal,which was conducive to the southward WPSH in September.The co-action of SSTA evolution and intra-seasonal variability of tropical convective activity led to the significant intra-seasonal variability of precipitation in autumn 2020.