Abstract:

Based on the monthly precipitation and average temperature at 86 meteorological stations of Southwest China, NCEP/NCAR reanalysis data with 2.5°×2.5° spatial resolution, monthly sea surface temperature from NOAA and OA index from CPC from January 1951 to April 2013, the causes of two continuous severe drought events which occurred in Southwest China from autumn 2009 to spring 2010 and from autumn 2012 to spring 2013 were compared from different aspects. The results showed that the anomalies of large scale atmospheric circulation and divergence of water vapor transport flux of the tropical western Pacific, the Bay of Bengal, the Indo-China Peninsula and the eastern Tibetan Plateau had remarkable influence on the two continuous drought events. Meanwhile, the abnormal impact of sea surface temperature (SST) in the tropical Indian Ocean and the Arctic Oscillation (AO) could not be ignored. The Southwest China controlled by the strong sinking motion, and the abnormal circulation and continuous warming of SST in the tropical Indian Ocean led to a weak water vapor transport from the Bay of Bengal during autumn and winter of 2009 and 2012. In addition, the divergence of water vapor transport flux was stronger. So the dynamic factors and moisture conditions were unfavorable for precipitation. The sustained negative phase of AO played an important role to the two drought processes in Southwest China, which not only made the southern trough weaken and shallow so as to reduce the water vapor transportation of the southwesterly airflow, but also weakened the Lake Baikal ridge and resulted in the moving path of the boreal cold air shifting eastward, which was not beneficial to the intersection of warm and cold air over Southwest China. The anomalies of SST in the tropical Pacific Ocean were not direct reason of the two continuous droughts, and the impacts on the two continuous drought events were different. The continuous drought in 2009/2010 occurred with an El Nino event, while in 2012/2013 it was affected by La Nina event.

Key words: continuous drought, atmospheric circulation, water vapor transportation, tropical sea surface temperature, Arctic Oscillation

摘要：

利用多种资料从不同方面对2009/2010、2012/2013年西南地区秋冬春季持续严重干旱进行对比分析，结果表明：这2次季节连旱都受热带西太平洋、孟加拉湾、中南半岛和青藏高原东部等地区环流异常、水汽输送通量散度异常、热带印度洋海表温度异常以及北极涛动（AO）异常的影响。2009年和2012年秋冬季，西南地区均受较强的下沉运动控制，环流形势异常和热带印度洋海表异常增温，导致来自孟加拉湾的水汽输送偏弱，同时该地区水汽输送通量辐散偏强，动力因子和水汽条件都不利于降水；AO持续负位相是引起持续干旱的重要原因，它不仅使南支槽减弱变浅，西南水汽输送减少，还致使贝加尔湖脊系统偏弱，北方南下冷空气主体偏东，不利于冷暖空气在西南地区上空交汇。热带西太平洋海表温度异常并非2次干旱事件的直接原因，且对这2次干旱的影响有所不同，其中2009/2010年的干旱发生在El Nino Modoki事件背景下，2012/2013年则受到弱的La Nina事件的影响。

关键词: 持续干旱, 大气环流, 水汽输送, 热带海表温度, 北极涛动