利用1981-2013年中国160站逐月降水资料、NCEP/NCAR逐月再分析资料及NOAA海表温度资料,研究了华南前汛期降水年代际异常的时空特征及其可能成因.结果表明:1)华南前汛期降水在1992前后发生由异常偏少转为偏多的显著年代际转折,最显著异常中心位于广西东北部和广东北部.2)1990年代初发生的对流层高层南冷北暖(40°N附近为界)、对流层下暖上冷的年代际转折,使得高低层环流场均出现了有利于北方干、湿冷空气和孟加拉湾、西太平洋暖湿水汽在华南区域交汇并辐合上升的形势,造成华南前汛期降水发生偏少转偏多的显著年代际转折.年代际转折的前后两个时段中,位于热带的孟加拉湾槽、东亚沿岸EAP遥相关型波列中的西太平洋副高、阿拉斯加湾附近的脊,以及中纬度贝加尔湖以西以南脊的强度或位置均具有显著差异,故这些环流系统的年代际异常是华南前汛期降水年代际异常的重要原因.3)南太平洋关键区海温在1990年代初开始呈现增暖趋势,在偏暖(偏冷)时期,华南低空受异常气旋(异常反气旋)环流控制,对流层上层西风急流偏弱偏南(偏强偏北),造成华南地区降水异常偏多(偏少).%Based on the monthly rainfall data at 160 stations of China,the NCEP/NCAR reanalysis dataset,and NOAA sea surface temperature dataset during 1981-2013,this paper investigates the spatial and temporal distributions of interdecadal precipitation anomaly and its possible causes during the first rainy season in South China.Results show that:(1) Precipitation during the first rainy season in South China has an significant interdecadal turning from negative to positive anomalies,which occurs around 1992,and the center of the most evident anomaly locates in northeast Guangxi and north Guangdong.(2)The significant interdecadal changes in 1990s when Southcold-North-warm in the upper troposphere (40°N bounded) and Lower-warm-Upper-cold in the troposphere occur,make the high-low level circulation field presenting a favorable situation,which is favor of the cold air from the north meeting with the warm and wet water vapor from Bay of Bengal and western Pacific and makes a rising situation of convergence in South China.The 500 hPa meridional circulation at mid-latitude enhances,the Bay of Bengal trough deepens in tropics,the East Asia-Pacific (EAP) pattern shows "+-+" anomalies from south to north,the western Pacific subtropical high is strong and southward,the 850 hPa wind field has an abnormal anticyclone(abnormal cyclone) circulation east to the Philippines(from Hetao of China to Japan Sea),South China is controlled by a cyclone circulation,and the subtropical westerly jet at the upper troposphere is weak and southward.These all result in a significant interdecadal turning of precipitation from less to more during the first rainy season in South China.During the two periods before and after the interdecadal turning,there are significant differences in the strength and position of the Bay of Bengal trough over the tropical,the western Pacific subtropical high and the ridge near the Gulf of Alaska in EAP teleconnection wave train,and the ridge to the south and the west of Lake Baikal over the mid latitude,so the interdecadal anomalies of these systems are the important reasons leading to the precipitation anomaly during the first rainy season in South China.(3)The interdecadal anomaly of sea surface temperature in the key region of South Pacific has great effects on the general atmospheric circulation in East Asia and precipitation in South China during the first rainy season.Sea surface temperature in the key area of South Pacific shows remarkable warming trend in the early 1990s.During the warm(cold) period,South China is controlled by the anomalous low altitude cyclone (anticyclone) circulation,and the upper-tropospheric westerly jet is weak and southward(strong and northward),which makes the abundant(lack) of precipitation in South China.
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