2009/2010年我国西南秋冬春连旱特征及其大气环流异常分析

利用中国逐日站点降水资料、逐日季风监测指数及逐日副热带高压指数、74项环流指数及NCEP/NCAR再分析资料, 分析了2009年秋季至2010年春季的秋冬春西南特大干旱过程中各指数及大气环流异常特征.结果表明: 自2009年10月底东亚冬季风建立以来, 至2010年春季, 东亚冬季风强度持续偏强, 加之西太平洋副热带高压较常年偏西偏南, 西南地区长期受副高控制, 气温持续偏高, 加之冷空气虽然总体偏强, 但主要控制我国北方地区, 造成冷暖空气在西南地区少有交汇, 致使降水偏少, 干旱发生发展. 印缅槽强度较常年偏弱, 来自印度洋、孟加拉湾以及南海的水汽条件不足, 向西南地区输送的来自南海和孟加拉湾两条水汽通道的水汽通量均较常年偏弱很多, 加之西南地区、特别是云南地区自2009年秋季以来, 长期处于下沉运动的正距平区, 造成这段时间西南地区干旱少雨, 旱情持续. 2009年9月El Niño事件全面爆发, 南海-西太平洋地区形成异常反气旋流场, 该反气旋流场较常年偏西偏南, 造成副高位置偏西偏南, 从而使得云贵高原及其周边的印度季风区的降雨量明显偏少;高原地区及南海、菲律宾附近及热带辐合带地区OLR异常对西太平洋副热带高压的变化有一定影响, 进而影响西南地区降水, 其内在机制还有待深入研究.

The Features of Continuous Heavy Drought from Autumn, 2009 to Spring, 2010 in Southwest China and Analysis of Its Atmospheric Circulation Anomalies

In order to study the features and causes of the drought disasters, the drought events and their atmospheric circulation anomalies in Southwest China from autumn, 2009 to spring, 2010 was examined by using observed daily precipitation data, daily East Asia monsoon index, daily subtropical high index, 74 atmospheric circulation indices and NCEP/NCAR reanalysis data. The results show that: 1) The continuous stronger East Asia monsoon and western Pacific subtropical high by west by north led to Southwest China controlled by western Pacific subtropical high and higher air temperature due to East Asia monsoon established from the end of October, 2009. A stronger cold air controlled northern China, precipitation occurred mainly in the North China and East China, so less cold air and warm air intersected over Southwest China and drought disaster occurred and developed. 2) The India-Burma trough was weaker than mormal, so moisture from the Indian Ocean and the Bay of Bengal was not enough. Both water vapor fluxes from the Bay of Bengal and from the South China Sea were under the normal. The Southwest China was located in a sinking motion anomaly region since autumn of 2009, causing continuous drought. 3) In September, 2009, an El Niño event took place, triggering atmospheric circulation anomalies, which resulted in an anomalous anticyclonic flow field in the South China Sea and the western Pacific. The anticyclonic flow field shifted to west and south of normal position, so the western Pacific subtropical high position shifted to west and south of normal position. At the same time, cold air was difficult to move southwards, affecting the Southwest China;the India monsoon was decline, the warm moist air flows from the Indian Ocean decreased with less vapor, so the rainfall in Indian monsoon regions of the Yunnan-Guizhou Plateau and its surrounding was less. 4) The OLR anomalies on the Tibetan Plateau and the South China Sea, near the Philippines, and the intertropical convergence zone had a close relationship with the western Pacific subtropical high and precipitation in Southwest China.