“泰利”台风低压大暴雨过程冷空气与地形的作用

Cold Air Activities and Topographic Forcing in Severe Torrential Rainfall in Landing Typhoon Depression(Tailim)

利用常规观测和地面加密资料、自动站资料、闪电定位资料、雷达资料以及NCEP再分析资料,对"泰利"台风低压引发的异常强暴雨事件中纬度冷空气的影响及地形的作用进行了分析。结果表明:在华西地区大陆高压与副热带高压形成对峙的背景条件下,中纬度冷空气从850 hPa以下低层不断侵入台风低压的北部,增强了其北侧的东北气流,它与来自东部海面上的东风气流在台风低压北部形成汇合;随着中纬度冷空气主体进入江淮地区,台风低压的正压结构缓慢向东暖西冷的斜压结构转换,总能量的水平分布也由螺旋型涡旋逐渐演变为NE—SW向的椭圆型结构,斜压能量的补充有利于台风低压长时间维持;湿位涡正压项的分析表明,随着台风低压进入消亡期,其上空大气变为对流不稳定。行星边界层能量锋区的加强,触发了β中尺度对流系统,导致在台风低压消亡时出现强雷暴天气;强降水主要分布在大别山东麓和九岭山脉迎风坡上,地形对偏东气流的抬升作用有利于暴雨的增幅。

The influence of middle-latitude cold air and topographic forcing on the abnormally severe rainfall event induced by a typhoon depression in Jiangxi Province on 2 to 4 September 2005 is analyzed by using the conventional and intensive observational data, the new atmospheric probing data （including automatic weather station data, lightning localization data, radar images, satellite images）, and NCEP re-analysis data. The results show that under the background condition of the subtropical high confronting the land high in the Western China, the middle-latitude weak cold air invading the northern part of the typhoon depression from below unceasingly at the 850 hPa level led to the strengthening of the NE current on its north side; with the main cold air entering the area south of Jiangsu and Anhui provinces from the middle latitude, its barotropic structure transformed slowly into the baroclinic state of ＂warm in the east and cold west＂, and the horizontal distribution of the total energy also changed from spiral vortex to NE-SW structure, which confirms that the supplement of baroclinic disturbance energy is advantageous to the long- time maintenance of the typhoon low; the analysis of the barotropic part of wet potential vorticity indicates that it changed from the convective stability to the convective instability during the disappearing period of the typhoon low; the strengthening of the energy front in the planet boundary-layer triggered the generation of the meso-β scale convection system, which produced the severe thunderstorm weather; the severe precipitation mainly distributed on the windward slope east of the Dabie and Jiuling mountains, which demonstrates that the orographic lifting and convergence effect contributed greatly to precipitation enhancement.