2010年梅雨期间我国东部地区降水异常的成因

Analysis of precipitation anomalies in the middle and lower reaches of the Yangtze River during June—July of 2010

基于我国台站的逐日降水观测资料,根据2010年梅雨期间(6—7月)我国东部地区雨带的落区,将该年梅雨期间的降水划分为3个主要阶段:第一阶段为6月7—11日,雨带主要集中在长江中下游地区;第二阶段为6月18—22日,雨带中心南压至江南地区;第三阶段为7月7—17日,此时雨带北抬重回到长江中下游地区.结合NCEP/NCAR逐日的再分析资料,分析了上述3个阶段的环流特征,结果表明:1)雨带出现南北摆动的现象与强冷空气南下有关;2)在第一阶段和第三阶段,长江中下游地区分别处在暖式切变和弱的暖式切变的控制之下,是造成降水的主要原因;3)6—7月西太平洋副热带高压脊点位置明显偏西,脊线位置明显偏南,二者与长江中下游降水存在显著的负相关,3次强降水过程的发生时间都对应着西太平副热带高压位置偏西,降水发生的位置正好位于西太平洋副热带高压的北侧.

The precipitation anomalies during June-July 2010 in east China were divided into three stages according to the distribution of rain bands during Meiyu period,based on the daily precipitation dataset archived in meteorological stations in China. Rain bands concentrated in the middle and lower reaches of the Yangtze River （ MLYR） during the first stage（ June 7—11） ,then the rain center moved southward to regions south of the Yangtze River during the second stage（June 18—22）,while there still had precipitation peaks in the MLYR.Finally,rain band center moved back to the MLYR during the third stage（July 7—17）.The relationship between the circulation features and the west Pacific subtropical high anomalies during the three stages were analyzed using NCEP/NCAR reanalysis data.Results showed that the north-south migration of rain belt was closely related with strong cold air in-vasion from north during the second stage. The warm shear line and weak warm shear line appeared in the MLYR during the first stage and the third stage,respectively,which was the main cause of these two precipitation processes. Moreover,the water vapor flux convergence and plentiful vapor resources in the MLYR also favored the three heavy rains.A significant negative correlation is found between the west ridge point index of the western Pacific subtropical high and the precipitation processes in MLYR during June-July 2010.Thethree heavy precipitation processes are in correspondence with the westward of west Pacific subtropical high, while the precipitation just occurred in areas north of the western Pacific subtropical high.So we concluded that the western Pacific subtropical high anomaly is one of the main reasons of heavy rainfall from June to July in the MLYR.