近40年我国暴雨的年代际变化特征

利用1961—2019年华南192个地面气象观测站逐日降水资料，定义华南区域性暴雨过程的标准，客观定量评估华南区域性暴雨过程，确定华南年和前、后汛期暴雨过程强度序列，分析其次数和综合强度指数的气候特征及变化。利用NCEP/NCAR再分析资料，采用相关和合成分析方法研究华南前、后汛期暴雨过程强弱年的大气环流特征。结果表明，近59 a来华南共出现1 196次区域性暴雨过程，平均每年20.3次，有82.3%出现在汛期4—9月。
华南区域性暴雨过程年发生次数以0.45·（10 a）^-1的速率上升，而年强度指数以1.148·（10 a）^-1的速率显著增加，特别是后汛期增加最明显。在华南前汛期，高层西风急流加强，东亚大槽日本南段明显加强，副高加强西伸，低层华南位于南北气流的交汇处，有利于前汛期暴雨偏强。在华南后汛期，高层西风急流加强，中层中低纬东亚位势高度增加，低层南海和西太平洋气旋环流增强，中低纬北太平洋海平面气压降低，有利于南海和西太平洋台风的生成，有利于后汛期暴雨偏强。

Objective assessment and analysis of abnormal causes of regional rainstorm events in South China

Based on the daily precipitation data at 192 surface meteorological stations in South China from 1961 to 2019, the standard for regional rainstorm events in South China is defined, and all regional rainstorm events in South China are objectively and quantitatively assessed. The intensity series of rainstorm events in South China during a whole year, the first and the second flood seasons are determined. The climatic characteristics and changes of its frequency and comprehensive intensity index were analyzed. Based on NCEP/NCAR reanalysis data, the characteristics of atmospheric circulation in strong and weak years of rainstorm events in the first and second flood season in South China are studied by using correlation and composite analysis methods. The results show that there are 1196 regional rainstorms in South China in recent 59 years, with an average of 20.3 events per year. 82.4% of them occurred in the flood season from April to September. The number of annual regional rainstorm events in South China increased by 0.
45/(10a)^-1. The annual intensity index of regional rainstorm in South China increased significantly at a rate of 1.148·(10 a)^-1, especially in the second flood season. In the first flood season in South China, the westerly jet in upper levels intensifies, East Asian Trough in the southern part of Japan strengthened, and the subtropical high strengthened westward. Additionally, the low level South China was located at the intersection of the North-South airflow, so the rainstorm intensity in South China increased in the first flood season. In the second flood season of South China, the westerly jet in upper levels intensifies, the geopotential height of East Asia in the middle and middle latitudes increases, and the cyclonic circulation in the South China Sea and the Western Pacific increases. The sea level pressure in the North Pacific decreases in the middle and low latitudes, which is conducive to the formation of typhoons in the South China Sea and the Western Pacific. The rainstorm intensity in South China increases in the second flood season.