2005年6月华南致洪暴雨的大尺度环流特征及成因探讨

Features of the Large-Scale Circulation for Flash-Flood-Producing Rainstorm over South China in June 2005 and Its Possible Cause

摘要:

利用NCEP/NCAR的逐日再分析资料,分析了2005年6月华南致洪暴雨的环流背景及其可能成因。结果表明:2004-2005年经历的一次弱ElNino事件是2005年华南致洪暴雨的气候背景。与2005年夏季相比较,6月17-26日强降水期间,华南地区的视加热<Q₁>和视水汽汇<Q₂>异常强烈,并且<Q₁>和<Q₂>的高值带与该时段降水量分布非常相似,高值中心与雨量中心位置基本一致。阿拉伯海东岸和孟加拉湾地区的异常加热源在其西北侧强迫出的高层异常反气旋性环流,使得南亚高压加强偏西。我国大陆处于异常气旋性环流之下,不利于南亚高压北上,有利于南亚高压在青藏高原南部、华南地区维持,使得华南地区位于高空西风急流南侧的上升运动区,有利于该区域强降水发生和维持,形成洪涝。

关键词:华南;致洪暴雨;大尺度环流;视加热;视水汽汇

Abstract:

Based on the NCEP/NCAR daily reanalysis data,the circulation background of the flash-flood-producing rainstorm over South China in June 2005 and its possible cause are analyzed.The results show that the weak ElNino events during 2004-2005 was the climatic background of the rainstorm.Compared with summer in 2005,the apparent heating source <Q₁>and apparent moisture sink <Q₂>were exceptionally strong over South China during June 17-26,2005.And the center of high value bands of <Q₁>and <Q₂>were basically coincided with that of rainfall.The anomalous heating source over the east coast of Arabian Sea and the Bay of Bengal forced an anomalous anticyclonic circulation over its northwest at the upper level,leading to the strenthening and westward stretching of South Asian High(SAH).An anomalous cyclonic circulation controlled the Chinese mainland,which went against the northward movement of SAH,but favored the maintaining of SAH over the south of the Tibetan Plateau and South China,so South China areas just located in the updraft areas in the south side of the upper level westeries jet,which is frequently in favor of the formation and maintenance of heavy rain,and thus severe flood.

Key words:South China;flash-flood-producing rainstorm;large scale circulation;apparent heating source;apparent moisture sink