近10年海南岛后汛期特大暴雨环流配置及其异常特征

Circulation of Extreme Rainstorm and Its Anomalous Characteristics During Post-Flood Period of the Last Decade in Hainan Island

通过对2000年10月11—14日、2008年10月12—14日和2010年10月1—8日3次持续性特大暴雨典型个例的对比分析,总结了近10年来后汛期特大暴雨的环流配置和异常特征。研究结果表明,近10年后汛期特大暴雨个例的天气系统配置都具有非常相似的特征:在对流层上层,南亚高压位于南海北部上空,高层存在稳定的辐散区。在对流层中、低层,热带低值系统、中纬槽后冷高压和副热带高压三者之间的相互作用,使得南海北部地区南北向和东北—西南向气压梯度加大,海南岛上空锋区结构建立,涡旋增强和维持,同时诱发偏东低空急流;南海北部存在强盛的偏东风低空急流是后汛期特大暴雨的天气学特征中最显著的强信号,其由热带低值系统东北侧的东南风,冷高压前缘的东北风和副热带高压南缘的偏东风汇合而成。最强降水发生前急流核的变化呈现出自东向西移动,高度逐日上升,风速脉动剧烈三个明显的特征。后汛期特大暴雨过程中大尺度环流相对气候同期平均态的异常特征也很显著:北半球亚洲区内热带辐合带(ITCZ)异常活跃,南海季风槽和印度季风槽南撤速度缓慢,比常年平均异常偏北偏强。南亚高压的位置比常年同期明显偏东偏南,东亚中纬槽,副热带高压的强度也比常年明显偏强。异常偏强的天气系统配置为强天气的发生提供了有利的环流背景;造成暴雨增幅的水汽主要来自大陆冷高压东南侧的东北气流和副热带高压南侧的偏东气流。

With daily precipitation observation data in Hainan compiled by National Climate Centre of CMA and NCEP/NCAR reanalysis data,the atmospheric circulation of extreme rainstorm and its anomalous characteristics during post-flood period late rainy season in Hainan Island in the last ten years are investigated.Results show that the circulation configurations of extreme rainstorm cases have many similar characteristics.In the upper level,South Asia high is located in the north of South China Sea(SCS) and provides strong divergence.In the middle and lower levels,increasing pressure gradient induced by the interactions among tropical disturbances,the Northwest Pacific subtropical high(NWPSH) and East Asia middle-latitude trough are helpful to the formation of frontal zone,maintenance and reinforcement of tropical disturbance and induction of easterly low-level jet.The presence of strong low-level jet in north-central South China Sea is the most significant feature of extreme rainstorm cases in late rainy season,which consists of the southeast wind from the northeast side of tropical disturbance,the northeast wind from the front of cold high and the easterly wind from the south side of NWPSH.The core of low-leve jet shows three obvious characteristics of moving from east to west,daily gradual rising and strong wind speed fluctuation before the torrential rain occurs.The distinct characteristics are also manifested mainly in the anomalies of synoptic scale circulation of extreme rainstorm cases in comparison with the same period climatological mean;the Pacific intertropical convergence zone(ITCZ)is exceptionally active,SCS summer monsoon trough and Indian summer monsoon trough are stronger and retreat more slowly in comparison with the normal climatological means.The location of South Asia high is abnormally eastern and southern,and the intensities of middle-latitude trough and NWPSH are stronger than usual.The water vapor causing the enhancement of precipitation is transported by the northeast wind from the front of cold high and the easterly wind from the south side of NWPSH.