江南地区持续性暴雨过程的月内环流异常和形成机制分析

利用1951—2009年NCAR/NCEP再分析资料，使用多种统计分析方法识别出对江南地区持续性暴雨过程发生、发展有重要影响的月内环流异常特征，并结合天气分析方法对其影响机制进行初步分析。结果表明，过程发生前3—1周，环流异常特征在中纬度的欧亚地区、北太平洋和南半球印度洋集中分布，其中欧亚和南半球环流异常特征反映的是沿高空急流东传的Rossby波列。正是上述环流异常特征传播和生消所对应的环流异常调整，使得副热带高压（副高）、阻塞高压、梅雨槽等关键环流系统分阶段逐步发展到位，形成有利于过程发生的大尺度环流背景“锁相”特征。 

AN ANALYSIS ON GLOBAL CIRCULATION ANOMALIES AND FORMING MECHANISM IN THE PRECEDING MONTH OF PERSISTENT HEAVY RAINFALL EVENTS OVER THE SOUTH OF YANGTZE RIVER VALLEY

Based on the NCEP/NCAR reanalysis data for 1951—2009, significant global circulation anomalies leading up to persistent heavy rainfall (PHR) events over the South of Yangtze River valley (with 1-month lag) are investigated, and the mechanism that brought about the events are analyzed. The results show that during 3-1 weeks ahead of the PHR events, circulation anomalies are generally located in the Eurasia, the North Pacific Ocean and the South Indian Ocean, and the anomalies in the Eurasia and the South Indian Ocean are two Rossby wave like chains in the subtropical westerlies of the middle and upper troposphere. The dispersion and disappearance of these circulation anomalies made the major circulation of WPSH, the Okhotsk Blocking High and the Meiyu Trough the condition of a phase-lock, therefore causing the formation of circulation characteristics favoring the PHR events.