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中文摘要：
采用1961～2012年中国气象局753站降水和温度资料、NCEP/NCAR全球大气再分析资料、NOAA海表温度资料等,应用观测统计分析和全球大气环流模式NCAR CAM5.1数值模拟,基于标准化降水蒸散指数（SPEI）,对我国西南秋季干旱的年代际转折及其可能原因进行了分析。观测分析结果表明：（1）西南秋季干旱的主要分布型为全区一致型;西南秋季SPEI在1994年发生年代际突变,突变后（前）为偏旱（涝）期。（2）西南秋季偏旱期的主要环流特征是,西太平洋副热带高压位置偏西、面积偏大、强度偏强,南支槽偏弱,西南地区存在下沉运动。（3）热带东印度洋—西太平洋的海表温度年代际升高对西南秋季SPEI在1994年发生年代际突变有重要作用,该关键海区海表温度异常升高,一是会使秋季西南地区500 h Pa高度场偏高,南支槽减弱;二是产生偏强的Hadley环流,使得我国西南地区存在下沉运动;三是会在西太平洋激发气旋性环流,使我国西南地区被偏北气流控制,削弱了向我国西南地区的水汽输送,容易造成该地区的秋季干旱。应用NCAR CAM5.1全球大气环流模式进行了关键海区海表温度年代际变化的敏感性试验,验证了观测分析结果,即秋季关键海区海表温度年代际升高对西南秋季年代际变旱有重要作用。
英文摘要：
Based on the precipitation and temperature data of 753 observation stations in China for the period 1961–2012, as well as National Centers for Environmental Prediction/National Center for Atmospheric Research（NCAR） reanalysis and National Oceanic and Atmospheric Administration Extended Reconstructed Sea Surface Temperature v3 b data, this study uses the Standardized Precipitation Evapotranspiration Index（SPEI） to discuss the decadal shift of autumn drought in Southwest China and its possible causes through observational analysis and NCAR Community Atmosphere Model, version 5.1（CAM5.1） numerical simulations. The observational results show that the main distribution for the entire district of autumn drought in Southwest China is in the same phase, and the drought has been getting worse since 1994. It is also found that when the western Pacific subtropical high is positioned further west, and is larger and stronger than usual, it is drier in Southwest China. A weak Indo-Burmese trough and local vertical subsidence movement are also key atmospheric circulation factors for autumn drought in Southwest China. The autumn drought in Southwest China is significantly correlated with the sea surface temperature anomaly（SSTA） over the eastern Indian Ocean and western Pacific（EIWP） region, which is the key region for the cause of Southwest China experiencing more drought since 1994. The positive SSTA in this key region enhances the 500 h Pa geopotential height over Southwest China in autumn. It also induces cyclonic circulation around the western Pacific, and an enhanced Hadley cell. In such cases, Southwest China is controlled by both northerly wind and subsidence motion, reducing the amount of water vapor transported to Southwest China. A series of numerical simulations using NCAR CAM5.1 confirm the above observational results and show that the autumn positive SSTA in the EIWP region plays an important role in causing the autumn drought in Southwest China on the decadal scale.
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