2019/2020年冬季我国暖湿气候特征及成因分析

Characteristics and Causes Analysis of the Warm and Wet Winter in China in 2019/2020

2019/2020年冬季,我国大部分地区气温显著偏高,降水异常偏多,气候总体表现为"暖湿"的异常特征。异常成因分析表明:2019/2020年东亚冬季风强度较常年同期偏弱,西伯利亚高压异常偏弱,季节内冬季风强度阶段性变化特征显著;北极极涡收缩于极地,强度偏强,AO为异常偏强的正位相,乌拉尔山阻塞高压活动偏弱,东亚槽偏弱,欧亚中高纬以纬向环流为主;西太平洋副热带高压强度偏强、位置偏西偏北,印缅槽阶段性活跃,二者有利于太平洋和印度洋水汽向我国输送。受北半球环流异常的影响,我国冬季出现了"暖湿"的异常特征。进一步对东亚冬季风偏弱的可能原因分析表明:2019年秋冬季赤道中太平洋暖海温发展,2019年10月至2020年1月Nino3.4指数均大于0.5℃,这种类中部型El Nino海温异常有利于激发偏强、偏北的西北太平洋反气旋,进而抑制了东亚冬季风的发展和南下;此外,冬季北半球极涡收缩于极地,强度偏强,AO持续异常偏强的正位相,均不利于乌拉尔山阻塞高压的发展,且东亚大槽明显偏弱,共同导致了欧亚中高纬地区以纬向环流为主,东亚冬季风偏弱。

The temperature in most areas of China was significantly higher than normal,and the precipita-tion was more than normal in the 2019/2020 winter.The main causes are as follows.The East Asian winter monsoon(EAWM)and Siberian high were both weaker than normal during the 2019/2020 winter,with significant intraseasonal variation of EAWM.The Arctic polar vortex(APV)was contracting in the polar region,with a strong intensity.The Arctic oscillation(AO)was in a positive phase with a strong intensity.The activity of Ural blocking high and the East Asian trough were all weak.The Euro-Asia was controlled by zonal circulation.The West Pacific subtropical high(WPSH)was significantly stronger than normal with westward and northward position.India-Burma trough(IBT)was active periodically.The WPSH and IBT were beneficial to water vapor transportation from Pacific Ocean and Indian Ocean to China.Diagnostic analysis of possible mechanism for weak EAWM in the 2019/2020 winter indicates that the warm SST in the equatorial Pacific in the fall and winter of 2019 and aroused strong and northward anticyclone in the northwestern Pacific, suppressing the development and southward invasion of the EAWM. In addition, the strong APV, and positive AO were not conducive to the development of Ural blocking high. And the East Asian trough was obviously weak. All these elements jointly lead to the zonal circulation in the middle and high latitudes of Euro-Asia and the weak EAWM.