ENSO事件对云南及临近地区春末初夏降水的影响

Influence of ENSO Event on Rainfall Anomaly over Yunnan Province and Its Neighboring Regions during Late Spring-Early Summer

本文采用合成及相关分析的方法,应用55年中国降水资料、美国NOAA海表温度资料以及NCEP/NCAR再分析资料,研究了ENSO事件对我国云南及其邻近地区春末初夏降水的影响及物理机理。研究结果表明:(1)在ElNin～o(LaNin～a)年,云南大部分地区4～5月降水偏少(多),东部地区相关信号尤其明显;(2)大气环流分析显示在ElNin～o(LaNi～na)年,对流层低层阿拉伯海及孟加拉湾为东(西)风异常,孟加拉湾出现明显的反气旋(气旋)式环流异常,同时西北太平洋副热带高压增强(减弱);(3)水汽输送分析表明,ElNin～o(LaNin～a)年,孟加拉湾对云南水汽输送减弱(增强)且该地区有显著的水汽辐散(辐合);(4)200hPa高度场与云南降水指数相关分析说明云南春末初夏降水异常与印度洋—亚洲(IA)型遥相关的冬、春转变有关,ElNi～no(LaNin～a)年春末初夏大气环流不(有)利降水生成。以上事实表明,ENSO事件对云南春末初夏降水异常的影响与其对华南和江淮流域降水影响有明显的不同,其中孟加拉湾气旋环流异常增强所导致的向云南地区的水汽输送的显著增加,起着决定性的作用。

Using the monthly gridded precipitation data in China,the NOAA extended reconstruction sea surface temperature（SST） data,and the NCEP/NCAR reanalysis data,the authors investigate the impact of the ENSO on the interannual variability of late spring-early summer rainfall in Yunnan Province and the relevant physical mechanism.The analysis of composite and correlation study reveal a strong negative correlation between the rainfall anomaly in Yunnan Province and the Nin^o index.An El Nin^o（La Nin^a） event is concurrent with less（more） precipitation during late spring-early summer（April-May） in Yunnan Province.Further analysis of atmospheric circulation demonstrates that an El Nin^o（La Nin^a） event is coincident with an anomalous easterly（westerly） over the Arabian Sea and the Bay of Bengal in the lower troposphere,a stronger anomalous anticyclone（cyclone） over the Bay of Bengal,as well as a stronger（weaker） subtropical anticyclone in the northwestern Pacific Ocean.The correlation between height at 200 hPa and rainfall anomaly during late spring-early summer（April-May） in Yunnan Province reveals a relevant Indian Ocean-Asia teleconnection（IA） pattern.The water vapor transport indicates that during an El Nin^o（La Nin^a） event there is a stronger water vapor divergence（convergence） over the region.All above evidences demonstrate that,in comparison with the physical processes in controlling the interannual variation of the summer rainfall in southeastern China and the Yangtze River-Huaihe River valley,the conversion of Indian Ocean-Asia teleconnection pattern from winter to spring is dominant in determination of the rainfall anomaly in Yunnan Province during late spring-early summer,and particularly the increased water vapor transport associated with the intensification of the anomalous cyclone over the Bay of Bengal plays an important role.