中国西南秋季旱涝的诊断分析

为了分析中国西南秋季旱涝情况,利用西南地区东部1961~2012年的降水资料和区域旱涝指数对该地区秋季旱涝等级进行了评定,并运用NCEP/NCAR再分析资料与英国气象局海温资料对典型旱涝年的成因进行了探讨。结果表明,西南地区东部降水呈显著减少趋势,并在1990年左右发生了突变。旱年秋季,低层在南中国海附近为显著的气旋性环流异常,西南地区上空存在显著的下沉运动,涝年则相反。进一步分析发现,当西太平洋海温偏高时,可以激发罗斯贝波环流异常,对应在南中国海附近存在异常的气旋性环流,临近的西南地区东部处于异常的下沉气流控制,容易发生干旱,涝年则相反。此外,热带西太平洋海温于20世纪80年代中后期发生了由冷转暖的突变,这与随后西南地区东部秋季降水的突变密切相关。

Diagnosis of drought / flood events in Southwest China in autumn

Based on the precipitation data of the Southwest from 1961 to 2012 and a regional drought index,the drought/flood level of the eastern Southwest(ESW)in China was assessed; and then based on the NCEP / NCAR reanalysis data and British Bureau global SST data, the causes for severe drought/flood events were investigated. The results show that the autumn rainfall of the eastern Southwest China appears an obvious decline trend, and has undergone significant mutations around 1990. In drought year autumn, there exists significant subsidence with anomalous cyclonic circulation around the South China Sea at lower levels,and vice versa.Further analysis finds that anomalous warm sea surface temperature(SSTA)in Western Pacific can stimulate Rossby wave-like circulation anomalies with an anomalous cyclonic circulation near the South China Sea and its jacent region.ESW is controlled by the abnormal downward motion, which is conducive to the formation of the drought; and the opposite situation occurs in the wet years.Moreover,SSTA of western tropical Pacific changes abruptly from cooling to warming near mid-to-late 1980s, which is closely linked to the subsequent mutation of autumn rainfall of the eastern Southwest China.