川贵渝复杂地形下横槽诱发双涡贵州暴雨过程的数值模拟

Numerical simulation of a torrential rain process in Guizhou triggered by two vortices originating from a transverse trough over the Sichuan-Guizhou-Chongqing complex terrain

青藏高原大地形作用下,西南复杂地形区暴雨天气预报是一个十分重要和困难的科学问题。应用西南区域数值预报业务模式,结合业务常规观测和非常规观测资料,分析了2014年7月15日至17日发生在四川、贵州和重庆复杂地形下的一次由横槽诱发双低涡的贵州暴雨过程,得到:西南区域模式对这次暴雨过程的数值模拟结果与再分析资料有较好的对应关系,尤其是重现了降雨的落区、强度以及盆地涡与贵州涡的发生、发展过程。在暴雨过程中,两低涡垂直发展深厚,上升运动均伸展至对流层顶。涡度收支方面,盆地涡的发展主要源于涡度方程的散度项,而贵州涡的发展除了受散度项的显著影响外,平流项也起着重要作用。由于川渝盆地—云贵高原交界处地形、云贵高原横断山脉延伸区局地地形的作用,区域大气气旋式旋转的加强发展诱发了盆地涡和贵州涡。热力结构上,盆地涡的发生、发展在冷、暖气流交汇辐合区域内,而贵州涡则生成在暖区中,其降雨及加强更多地受到动力过程的影响。川渝盆地—云贵高原特殊的北低南高地形使高纬度干冷气流与低纬度暖湿气流交汇,形成强的上升运动,引发了盆地涡发展及其暴雨天气。云贵高原贵州特殊的西高东低地形导致来自低层的暖湿气流只能沿横断山脉边缘绕流,进入贵州西部的偏南气流与来自盆地涡西侧的偏东北气流汇合作用形成贵州涡,引发贵州暴雨天气。因此,局地地形与环流的相互作用是贵州涡生成及其引发暴雨过程的重要原因。

Under the influence of the Tibetan Plateau topography,torrential rain forecast in complex terrain area of Southwest China is a very important and difficult scientific problem.Based on operational and unconventional observations,the regional modeling system of Southwest China is used to analyze a two-vortex torrential rain event in Guizhou Province from 15 to 17 July 2014,which was caused by a transverse trough over the complex terrain area of Sichuan-Guizhou-Chongqing.Results show that the simulation agrees well with the reanalysis data.In particular,the range and intensity of rainfall and the occurrence and development processes of Basin Vortex in Sichuan-Chongqing Basin and Guizhou Vortex in Yunnan-Guizhou Plateau are well reproduced.During the torrential rain,the two vortices enhanced deeply in the vertical direction and the updraft extended to the top of the troposphere.In terms of the vorticity budget,the development of the Basin Vortex mainly originated from the divergence term.In addition to the significant influence of divergence term for the intensification of the Guizhou Vortex,advective transport also played an important role.Due to the complicated local topography at the junction of Sichuan-Chongqing Basin and Yunnan-Guizhou Plateau and the extension area of Hengduan Mountains in Yunnan-Guizhou Plateau,the intensification of cyclonic rotation in the regional atmosphere induced Basin Vortex and Guizhou Vortex.In terms of thermal structure,the Basin Vortex developed in the convergence area where cold and warm flows encountered.However,the Guizhou Vortex appeared in the warm area,and its rainfall and enhancement were more affected by dynamic processes.The special north-low and south-high terrain of Sichuan-Chongqing Basin and Yunnan-Guizhou Plateau made the dry and cold airflows from high latitudes intersect with the warm and humid airflows from low latitudes,forming strong ascending motions and triggering the development of Basin Vortex and torrential rain.The particular west-high and east-low topography of Yunnan-Guizhou Plateau caused the warm and humid air from low levels to circulate only along the edge of Hengduan Mountains.The southerly airflow entering the west of Guizhou and the northeasterly airflow from the west of the Basin Vortex formed the Guizhou Vortex,producing torrential rain in Guizhou.Therefore,the interaction between local terrain and circulation is an important reason for the formation of the Guizhou Vortex and torrential rain.