中文摘要：

利用西南地区5省市126个气象站1961―2009年逐月降水资料以及NCEP/NCAR月平均资料,分析了西南地区2009年秋季特大旱灾降水变化特征以及同期的环流特征。结果显示：（1）2009年秋季,来自孟加拉湾地区、南海地区暖湿水汽与来自内蒙古水汽均减弱;西南地区大部分地区水汽净获得减少或者由水汽净获得转换为水汽净失去。（2）2009年9―10月份西风带纬向环流较往年增强,西风槽偏东,东亚大槽西翼偏北;11月份西风带经向环流较强,但内蒙古西部、宁夏、甘肃、青海东部南下偏北风经向分量较往年减弱,西风槽偏北。（3）2009年9月份副高偏西偏强,西南在副高控制下,辐合上升水汽减少;10月份云南、贵州、广西大部分地区受控副高;11月份副高西伸至孟加拉湾地区,偏南风只存在17.5°N以北的孟加拉湾地区,这削弱了孟加拉湾地区向我国西南地区输送的水汽量。

英文摘要：

Monthly precipitation data of the 129 stations in Southwest China and the NCEP/NCAR data from 1961 to 2009 are used to analyze the rainfall anomaly and the atmospheric circulation features in autumn 2009. The results show that （1）both the warm moisture flux from the Bay of Bengal and the South China Sea and the cold moisture flux from Inner Mongolia decreased in autumn 2009,that made the interaction between cold and warm moisture flux weaken. （2）Moisture convergence reduced in Southwest China in September, and increased in November, when the moisture flux from the Bay of Bengal and the South China Sea decreased, that made rainfall decrease. （3）Zonal westerly circulation enhanced in September and October. In November, meridional westerly circulation became stronger, but the 700-500hpa meridional wind vector over the western Inner Mongolia, Ningxia, Sichuan weakened. （4）The West Pacific Subtropical High became stronger and moved west in September, and Southwest China was under its control, that made water vapor convergence reduced. In October,the West Pacific Subtropical High was over Yunnan,Guizhou and Guangxi. In November, the High stretched toward the Bay of Bengal, southerly wind only existed to the north of 17.5N, that made moisture flux from the Bay of Bengal weaken. Based on the above analysis, the authors think that water vapor flux anomaly, westerly circulation anomaly and the West Pacific Subtropical High being stronger and moving west are important factors affecting the autumn rainfall of 2009 in Southwest China.