广西前汛期降水变化特征及其与东南太平洋海温变化的因果联系

利用1979—2019年全国160站逐月降水资料、国家气候中心的西太平洋副热带高压特征指数逐月资料、英国Hadley中心逐月海表面温度资料以及NCEP/NCAR逐月再分析资料，结合小波分析、相关分析、信息流以及合成分析方法，分析了广西前汛期降水的变化特征及其与东南太平洋海温变化的因果联系。结果表明:近40 a来广西前汛期降水呈弱增多趋势，在1980年代末至21世纪初存在显著的3~5 a周期。在1980年代至1990年代初为少雨期，而在20世纪末至21世纪初期转为多雨期。东南太平洋是海温影响广西前汛期降水的关键区，同年春季以及同期该区域海温变化是造成广西前汛期降水变化的原因之一，海温升高(降低)能够部分导致降水的减少(增多)。同年春季海温偏冷年，关键区西侧为对流抑制，南太平洋出现异常反气旋环流响应，通过垂直环流引起澳大利亚西北侧上升运动异常，减弱了局地Hadley环流。该异常通过大气桥一方面使得副高增强增大，位置偏西偏南，有利于副高西侧的西南气流向广西输送水汽；另一方面使得广西地区上空局地Hadley下沉支减弱，受异常上升运动控制，对流增强，导致降水正异常。反之亦然。 

VARIATION OF ANNUALLY FIRST RAINY SEASON PRECIPITATION OVER GUANGXI AND ITS CASUAL RELATION WITH SEA SURFACE TEMPERATURE IN THE SOUTHEAST PACIFIC

The variation of annually first rainy season (FRS) precipitation of Guangxi and its casual relation with sea surface temperature (SST) in the Southeast Pacific are studied by using monthly precipitation data from 160 stations in China, National Climate Centre West Pacific Subtropical High (WPSH) indices, Hadley SST data and NCEP/NCAR monthly reanalysis data during 1979-2019, as well as the methods of wavelet analysis, correlation analysis, information flow and composite analysis. The results show that the FRS precipitation is characterized by a weak increasing trend over the past 40 years. The precipitation variation showed a significant 3-5 year oscillation from late 1980s to the early 21st century. During the FRS of Guangxi, there was less precipitation from 1980s to early 1990s while more precipitation from the end of 20th century to the beginning of the 21st century. Southeast Pacific is the key region where SST influences FRS precipitation over Guangxi, and the SST change in previous spring or at the same period contribute to the variations of FRS precipitation. Rise (drop) of SST may partly influence the decrease (increase) of precipitation. In negative SST anomaly years, convection suppression occurs on the west side of the key region, leading to an abnormal response of anticyclonic circulation in the South Pacific, which causes an abnormal upward movement on the northwest side of Australia and weakens the local Hadley circulation by influencing vertical circulation. On the one hand, influenced by this anomaly through the atmospheric bridge, the WPSH becomes stronger and larger, with a more westward and northward position which is conducive to the water vapor transport from South China Sea to Guangxi. On the other hand, this anomaly weakens the local Hadley sinking branch over Guangxi, which is controlled by the abnormal upward movement, enhancing convection, and ultimately causing more precipitation, and vice versa.