中文摘要：

利用1960～2011年广西西北部16个气象观测站逐月降水资料、NCEP/NCAR再分析月平均资料、NOAA向外长波辐射资料和国家气候中心提供的环流特征量资料,分析了广西西北部地区以往盛夏干旱年的中高纬环流、西太平洋副热带高压和水汽输送特征,重点探讨了2011年盛夏（7～8月）广西西北部特大干旱大气环流的异常特征。结果表明,2011年是1960年以来广西西北部盛夏降水最少的年份。广西西北部2011年盛夏大气环流与以往盛夏干旱年明显不同的是,西太平洋副热带高压较常年异常偏弱偏东,脊线位置明显偏北,中高纬环流平直,乌拉尔山地区和东北亚区域没有明显阻塞高压形势,冷空气活动比常年弱;印缅槽活动较常年偏弱,由南向北的水汽输送明显偏弱,广西西北部上空存在有弱的水汽通量辐散,垂直运动和对流活动均较常年偏弱,这些环流特征均不利于产生降水,造成2011年盛夏广西西北部地区出现特大干旱。

英文摘要：

On the basis of the NCEP/NCAR monthly mean reanalysis data, NOAA outgoing long-wave radiation data, circulation feature data given by the National Climate Center, and the monthly precipitation data of the 16 stations in northwestern Guangxi from 1960 to 2011, the characteristics of the middle–high latitude circulation, the western Pacific subtropical high（WPSH）, and the moisture transport for all the drought years are studied. In particular, the anomalous atmospheric circulation of the extremely severe drought occurring from July to August 2011 is examined. The results show that the midsummer precipitation in 2011 was the least since 1960. The extremely severe drought of northwestern Guangxi in midsummer 2011 is obviously different from other drought events. The WPSH was weaker and was eastward and shifted northward, and the straight flow prevailed over mid-high latitude region. In addition, no obvious blocking high over the Ural Mountains and Northeast Asia was noted. Moreover, the cold air activities, the activities of the India–Burma trough, water vapor transport from south to north with weak positive moisture flux divergence, vertical movement, and convective activities in midsummer 2011 were all weaker than normal. All of these features are not conducive to precipitation and jointly resulted in the extremely severe drought event in northwestern Guangxi.