西南地区秋季干湿时空变化特征及其成因分析

THE SPATIO-TEMPORAL VARIATION OF AUTUMN DRY-WET CONDITION IN SOUTHWEST CHINA AND THE ANALYSIS OF ITS POSSIBLE CAUSES

利用西南地区97站1960—2009年的日平均气温、降水量资料计算干湿指数,分析了西南地区秋季干湿、降水、气温的时空变化特征,并使用再分析资料探讨其异常的大气环流特征。结果表明:西南地区秋季在1980年代末期出现干旱化趋势,21世纪初干旱化趋势明显,其中以东部干旱化趋势显著。西南地区秋季干湿变化存在全区域一致和东、西部相反变化两个主要异常模态,而且干湿异常的空间模态主要由降水异常决定,其演变则受气温的影响更明显一些。全区域一致变化的模态与前期夏季西太平洋暖池附近海温以及同期西太平洋副高、东亚大槽、南支槽有关,并且此模态对应的偏干年基本上均是高温和少雨共同作用造成的,而偏湿年则有低温偏湿和多雨偏湿两种类型。东、西部相反变化的模态与垂直运动和东部低层的南、北风异常有关。

Based on the daily precipitation and daily mean temperature data of 97 stations in Southwest China （SW China） form 1960 to 2009, a dry-wet index is calculated. The spatiotemporal variation characteristics and their circulation characteristics of the autumn dry-wet index, precipitation and temperature are studied. The results show that the trend of drought appears in the late 1980s and becomes significant in the early 2000s. The drying trend is significant in the eastern SW China. There are two main modes of autumn dry-wet variation in SW China. One is consistent across the whole region and the other is a dipole in the latitudinal direction. The spatial distribution of dry-wet variation is mainly affected by precipitation and its evolution is largely affected by temperature. The former mode is affected by the anomalies of the precedent SST near the Western Pacific Warm Pool, the Western Pacific Subtropical High, the East Asian Trough and the South Trough. The latter mode is related to the wind anomalies in the eastern SW China and the vertical movement in the western and eastern SW China. These are the main influencing factors for the autumn dry-wet variation in SW China, which have a great significance on the prediction of drought.