Rossby波和热带对流活动对2010年6月梅雨发生前后我国东部两次强降水过程的影响

基于574台站的逐日降水资料及NCEP/NCAR逐日再分析资料,在比较2010年梅雨期前后(6月7—11日和18—22日)我国东部两次强降水过程的大尺度环流型差异的基础上,从Rossby波活动通量及热带对流活动探讨了这两次强降水过程的异同。结果表明,相同之处在于:两次强降水过程期间中高纬度地区都存在Rossby波向下游传播,中纬度地区呈现双阻型式,低纬度地区西太平洋副热带高压(以下简称西太副高)强度偏强、西伸脊点位置偏西。不同之处在于:1)第一次降水过程中Rossby波的波源位于北欧地区附近,贝加尔湖地区为低槽,使得冷空气南下到36°N左右;同时孟加拉湾活跃的对流系统使西太副高加强西伸到95°E左右,冷暖空气交汇,导致强降水发生;2)第二次降水过程中Rossby波的波源位于北欧地区和中西伯利亚地区附近,东亚地区的低槽较第一次过程明显加深,有利于冷空气到达长江中下游地区(30°N左右),西太平洋暖池地区活跃的对流系统使得西太副高加强西伸到90°E左右,冷暖空气在长江中下游及其以南地区交汇,导致强降水发生。

The impact of Rossby waves and the tropical convection activities on two precipitation events occurring before and during the June 2010 Meiyu period

In this study,using daily data from the NCEP/NCAR reanalysis dataset and precipitation observations recorded at 574 stations,two heavy rainfall processes during the periods of June 7-11 and 18-22,2010 occurring in the middle and lower reaches of the Yangtze River(MLRYR) are compared based on their respective circulations,Rossby wave activity fluxes,and tropical convection activities.The results show that a downstream propagation Rossby wave and double-block high were present in the mid-high latitudes throughout the time when these two processes occurred.During these events,it is shown that the intensity of the western Pacific subtropical high(WPSH) was stronger and the western extension point was more westward than normal in the low latitudes.However,two major differences are observed between the events:1)The source of the Rossby wave was located in northern Europe.Due to a low-pressure trough over the Lake Baikal area,the cold air turned southward to about 36°N.At the same time,the strengthened and westward WPSH were located at about 95°E.Next,the cold and warm air converged,leading to heavy rainfall.2)The source of the Rossby wave was located in northern Europe and central Siberia.The low-pressure trough in East Asia was more prominent than in the first rainfall process,which was conducive to the cold air reaching the MLRYR(about 30°N).In addition,the westward extension of the WPSH was located at about 90°E.The cold and warm air converged in the MLRYR and in its southern area,thereby leading to heavy precipitation in these regions.