影响华南后汛期季风持续性暴雨和热带气旋持续性暴雨的大尺度环流背景分析

COMPARED ANALYSIS CHARACTERISTICS OF IMPACT OF LARGE SCALE CIRCULATION ON THE PERSISTENT HEAVYRAINS IN POST-FLOOD SEASON IN SOUTH CHINA ASSOCIATED WITH MONSOON AND TROPICAL CYCLONE

利用1961—2008年NCEP逐日、逐月再分析资料和全国和华南各省台站逐日降水资料,得到华南后汛期持续性暴雨74例,其中热带气旋(TC)引起的持续性暴雨(TCR)有54例,季风引起的持续性暴雨(MSR)有20例。TCR主要发生在8月,占TCR总数的52%,MSR主要发生在7月,占MSR总数的70%。两类持续性暴雨的出现次数具有明显的年代际变化特征,自1980年代以来发生的次数明显增加。通过对比分析得到,MSR主要由前期和同期热带中东太平洋异常海温持续偏暖所致,其一方面加强了南海夏季风环流、水汽辐合异常增强;另一方面增强了菲律宾海的对流,使得高空西风急流位置偏北;在两者的共同作用下,大气环流激发出"-、+、-"的EAP遥相关型波列分布,为7月持续性暴雨的发生提供有利条件。相比之下,TCR主要由于8月局地海温-黑潮区海温异常偏冷致使高空西风急流位置偏北所致。此外,叠加在这种尺度背景下,导致MSR和TCR发生的关键是10~20天季节内振荡导致系统由东南向西北传播。

Based on the NCEP daily and monthly reanalysis data and the daily rainfall records from 743 stations and South China stations in China during 1961--2008, it is found that there exist 74 persistent heavy rainscases in post-flood season in South China, including 54 cases caused by tropical cyclones （TCR） and 20 cases caused by monsoon （MSR）. For the TCR mode, it mainly occurred in August, which accounts for about 52 percent of the total numbers of TC persistentheavy rains.For the MSR mode,it mainly happened in July, which account for about 70 percent of the total numbers of monsoon persistentheavy rains. It illustrates obvious interdecadalincreasing variation characteristics since 1980 for both two modes. When the continuous warm surfaces sea temperature anomalies （SSTA） in the Middle and East tropical Pacific happened in the preceding and simultaneous period,the South China Sea summer monsoon circulation canbe strengthened, which resulting in the water vapor abnormal convergence. In addition, the SSTA may lead to the westerly jet positionmore northwardthroughenhancing the convection of the Philippine Sea.Such environmental conditions favor ＂-, ＋, -＂ Meridional wave train anomalies teleconnection pattern for MSR in July. By contrast, TCRinAugust is attributed to the westerly jet more northward position, caused by local cold SST anomalies such as like the kuroshio area SST. Superimposed on the large scale circulation, 10-20-day intraseasonal oscillation propagation characterized by a northwest-southeast oriented wave train pattemis mainly responsible for MSR and TCR.