厄尔尼诺次年广西前汛期降水量差异成因分析

Analysis of the causes of precipitation differences during the first rainy season of Guangxi in the following year of El Nino

利用1981年以来广西前汛期降水量、NCEP/NCAR再分析资料、英国Hadley中心海表面温度资料以及国家气候中心的大气环流指数、海温指数和积雪指数等资料,采用合成、相关计算方法,分析了厄尔尼诺次年广西前汛期降水量差异的成因。结果表明,厄尔尼诺次年广西前汛期降水偏多时,500hPa副热带高压更强更大更偏西,乌拉尔山高压脊偏强但东亚槽偏弱,西西伯利亚分裂西风槽东移,引导冷空气主要从西路、中路南下影响广西。外强迫因子中,NINO3.4、IOBW、青藏高原积雪面积和西太副高强度、脊线和西伸脊点正相关,NAT则为反相关;IOBW、SIOD对东亚槽强度作用相反,IOBW正位相有利于东亚槽偏弱,SIOD正值则东亚槽偏强;TIOD、SIOD负值有利于贝湖至巴湖高度值低,不断分裂西风槽东移南下。因而不同的海温关键区分布形态和高原积雪面积配置引起500hPa影响系统的差异,从而造成厄尔尼诺次年广西前汛期降水量的差别。

Based on the precipitation data during the first rainy season(FRS)in Guangxi since 1981,NCEP/NCAR reanalysis data,the sea surface temperature(SST)data of the Hadley Center in the UK,the atmospheric circulation index,SST index,and snow cover index from the National Climate Center,the causes of the precipitation difference during FRS in Guangxi in the following year of El Nino were analyzed by using synthesis and correlation calculation methods.The results show that the Western Pacific subtropical high(WPSH)at the level of 500hPa is stronger,larger and more westward when there is more precipitation in FRS of Guangxi and it occurs in the following year of El Nino,and the Ural Mountains high-pressure ridge(UMH)is stronger,but the East Asian trough is weaker,and the westerly trough is split from the western Siberian which guides cold air southward from the west or middle route affecting Guangxi.Among the external forcing factors,NINO 3.4,IOBW,snow cover of Tibetan Plateau is positively correlated with the intensity,ridge lines,and western extension ridge points of WPSH,which are negatively correlated with NAT.Moreover,the effects of IOBW and SIOD on the strength of the East Asian trough are opposite,with positive IOBW phase favoring a weak East Asian trough and positive SIOD favoring a strong East Asian trough.Additionally,negative values of TIOD and SIOD are conducive to low geopotential height values from Lake Balkhash to Lake Baikal,which continuously split the westerly trough and moving eastward and southward.Therefore,different configurations of key SST zones and plateau snow cover areas cause the differences in the 500hPa impact systems,resulting in differences in precipitation during FRS of Guangxi in the following year of El Nino.