四川南部秋季降水变化及相应大气环流异常特征

利用1961—2014年全国756站的降水资料和美国NOAA-CIRES的20CR月平均再分析资料,研究了四川南部秋季(9～11月)降水变化及其相应的大气环流异常特征。结果表明,四川南部秋季降水具有显著的年际和年代际变化特征,其年际周期以2～4 a和准6 a为主,年代际周期以9～15 a为主。它与黄淮流域同期降水存在显著的负相关关系,与四川南部秋季降水关系密切的大气环流结构是北大西洋—俄罗斯西部—蒙古西部—东亚(NRMA)遥相关波列,NRMA遥相关波列在东亚地区激发出一个气旋性环流,与此同时,中南半岛西侧存在一个反气旋性环流,以上环流型有利于北方冷空气和来自孟加拉湾的暖湿气流在四川南部地区汇合,从而容易导致该地区降水的产生,反之亦然。

Variability of Boreal Autumn Rainfall over the Southern Sichuan and the Associated Atmospheric Circulation

The variability of the boreal autumn rainfall over the southern Sichuan and its associated atmospheric circulation during the period 1961-2014 are investigated based on the station rainfall data from the Chinese Meteorological Data Center and atmospheric data from the National Oceanic and Atmospheric Administration-Cooperative Institute for Research in Environmental Sciences (NOAA-CIRES) 20th Century Reanalysis V2c dataset. The results show that rainfall over the boreal autumn rainfall over southern Sichuan is characterized by significantly interannual and interdecadal variability. On the interannual time scale, rainfall variability over the southern Sichuan has significant periodicities of 2-4-years and quasi-6-years, respectively, whereas on the interdecadal time scale, it has a significant periodicity of 9-15-years. Besides, the boreal autumn rainfall over the southern Sichuan has a significantly out-of-phase relationship with the simultaneous rainfall variability over the Yellow River-Huaihe River region. Further analysis shows that the dominant atmospheric circulation pattern associated with the boreal autumn rainfall variability is the North Atlantic-western Russia-western Mongolia-East Asia (NRMA) wave train, which can result in a significantly anomalous cyclone over East Asia. Moreover, there is an anomalous anticyclone over the western Indochina Peninsula. This distribution of atmospheric pattern is favorable for convergence of the warm and moisture southwesterly anomalies from Bay of Bengal and the cold and dry northeasterly anomalies from North China, and thus inducing more rainfall over the southern Sichuan.