北京“7.21”特大暴雨过程中尺度系统的模拟及演变特征分析  

Simulation and Evolution Characteristics of Mesoscale Systems Occurring in Beijing on 21 July 2012

作　　者：周玉淑[1] 刘璐[1,2] 朱科锋[3] 李建通 

机构地区：[1]中国科学院大气物理研究所,北京100029 [2]中国科学院大学,北京100049 [3]南京大学大气科学学院,南京210093 [4]厦门市气象局,厦门361012

出　　处：《大气科学》2014年第5期885-896,共12页Chinese Journal of Atmospheric Sciences

基　　金：国家重点基础研究发展计划项目2009CB421505;国家自然科学基金资助项目41275065;41375054;41075044

摘　　要：在2012年7月21日北京特大暴雨过程天气尺度环流背景分析的基础上,主要用WRF模式对该次暴雨过程进行了高分辨率的模拟。利用模拟资料分析了影响此次北京特大暴雨的辐合线及辐合线上生成的中尺度低涡的热动力结构及其演变。从热力场来看,来自于西北和东北方向的强冷空气与西南和东南暖湿气流的长时间对峙形成的辐合以及中低层冷空气从西北和东北方向向西南的入侵迫使整层暖湿空气抬升,以及低空急流的暖湿平流与低空弱冷空气之间形成的"西冷东暖"的结构,对对流不稳定的触发有一定作用,有助于该次特大暴雨的发生。对流层低层的西(东)南风与西北风之间形成了一条持续时间长的辐合切变线,切变线上不断有中尺度低涡生成并沿切变线发展移动,模拟资料分析表明,低涡不断沿切变线生成并移动经过北京从而对该次暴雨造成影响,这与"列车效应"现象类似。切变线上生成的中尺度低涡位置也同时处于急流左前侧和山前,低涡加强和发展时对应有暴雨的明显增强,是直接造成北京特大暴雨的中尺度系统,其生成与低层辐合、低空急流及地形均有关系。低层辐合引发的垂直运动在地形迎风坡附近得到加强,低层辐合及地形抬升共同导致了强垂直运动的发展和维持,是暴雨持续的重要原因。大气中层有下沉气流与低层上升气流相互作用,在大气中低层形成一系列中尺度环流,房山附近一直有中尺度环流的垂直上升支维持,也是暴雨中心出现在房山的原因之一。Abstract On the basis of synoptic circulation pattern analyses of the torrential rain occurring in Beijing on July 21,2012, the thermal and dynamical structure of the convergence line and the mesoscale vortex above it was analyzed by using output data of the high-resolution Weather Research and Forecasting （WRF） model. A convergence line formed between the strong, cold air from the northwest and northeast and the warm, moist air from southwest and southeast. The latter was lifted by mid-low-level invasion of the northern cold air, which triggered convective instability. The mesoscale vortex was generated and appeared continuously along the persistent convergence shear line in the low-level troposphere, which is similar to the influence of the train effect in torrential rain. The mesoscale vortices were generated at the left of low-level jet, which was located near mountain, and became the direct reacting system for the torrential rain. The precipitation was amplified with the enhancement of the vortices. This vortex formation was related to the low-level convergence line, the low-level jet, and the terrain. The vertical motion caused by the low-level convergence was enhanced by orographic lift, which is attributed to the persistence of the heavy rain. The lifted air appeared in upward and downward branches when contacting the western air flow at middle levels, and a series of the cyclonic mesoscale secondary circulation at lower levels was triggered when the downward branch mingled with the upward air current at those levels. An updraft was persistent above Fangshan district was the main cause for the torrential rain in that location.

关 键 词：暴雨 数值模拟 结构分析 中尺度低涡 

分 类 号：P445[天文地球—大气科学及气象学]