2012年4月华南地区降水异常事件及成因诊断分析

基于实时、历史观测资料和NCEP/NCAR 再分析资料,采用气候统计和气候事件机理诊断分析方法,对2012 年4 月华南地区降水异常事件及其成因机制开展总结分析。结果表明:2012 年4 月华南大部地区降水异常偏多,强降水频发。华南地区降水异常事件的主要成因为:异常的高低纬环流形势配合,为华南地区降水异常偏多提供有利的环流背景,利于北方冷空气南下与西南暖湿气流在华南地区交汇;同期华南地区为异常偏强的上升气流控制,高低空辐散、辐合环流配置利于华南地区降水异常偏多;源自孟加拉湾、南海和西太平洋的异常水汽输送为华南地区提供良好的水汽条件,是华南地区降水异常事件的重要影响因子。

Abnormal Precipitation Event and Its Possible Mechanism over South China in April 2012

Based on the daily real-time, historical observation data and NCEP/NCAR reanalysis data, the characteristics of abnormal precipitation event and possible mechanism in South China during April 2012 were analyzed by the climatic statistics and climate event diagnostic methods. Results showed that the cumulative precipitation amounts were observed evidently more than normal in most South China during April 2012, with the regional averaged precipitation amount ranking as the maximum value for the same period since the year of 2001. Moreover, the abnormal precipitation event caused rainstorm and flooding disasters in parts of South China. Taking above precipitation event as a case study from monthly time scale, key factors affecting the variation of precipitation in the pre-summer flood season of South China were explored. The author analyzed systematically the possible formation mechanism for the abnormal precipitation event in South China from the perspective of atmospheric circulation system anomaly and moisture transport. The major findings are as follows: Firstly, The abnormal rainfall over South China during April 2012 was a direct result of contemporary atmospheric circulation anomalies. The favorable atmospheric circulation pattern with positive anomaly of geopotential height over the Ural mountain area and negative anomaly of geopotential height over most China and Mongolia, meanwhile, the South China Sea and northwest Pacific region controlled by abnormal anticyclonic circulation in the lower troposphere, benefited the cold air moving to South China and converging with the southly warm-wet air on South China. Thus the coordinated atmospheric circulation anomalies in higher latitude and lower latitude area provided favorable circulation backgrounds for the occurrence of abnormal precipitation event during April 2012. Meanwhile, most of South China was controlled by the atmospheric upward motions over the study period, with concomitantly divergence in upper-troposphere and convergence in lower- troposphere, thus vertical circulation system gave rise to the anomaly of precipitation in South China. Moreover, the stronger southwestly moisture was transported from Bay of Bangal, the West Pacific and South China Sea to South China, which was the center of convergence of moisture flux transport during April 2012, especially in the central and eastern parts of South China. The abnormal southwestly water vapor transporting from ocean to South China provided material conditions for the occurrence of abnormal precipitation event. All above mentioned have caused the abnormal precipitation event in South China during April 2012．