“7·21”北京特大暴雨成因分析(Ⅱ):垂直运动、风垂直切变与地形影响  

Analysis on the cause of a torrential rain occurring in Beijing on 21 July 2012(Ⅱ):vertical motion,wind vertical shear and terrain effect

作　　者：孙明生[1,2] 杨力强 尹青 牛震宇 高黎明 

机构地区：[1]北京军区空军气象中心 [2]中国气象科学研究院国家灾害天气重点实验室 [3]93420部队52分队气象台

出　　处：《暴雨灾害》2013年第3期218-223,共6页Torrential Rain and Disasters

基　　金：中国气象科学研究院灾害天气国家重点实验室开放课题(2012lasw-B07LASW)

摘　　要：本文是"北京7·21特大暴雨成因分析"的第二部分,从上升运动、风垂直切变以及地形影响等方面进一步探讨暴雨成因。所用资料包括常规、加密自动气象站、多普勒雷达观测以及NCEP 1°×1°再分析资料。分析表明:1)高空急流辐散与低层低涡切变线、地形辐合线、地形强迫抬升等共同作用构成的强烈上升运动触发和增强了暖区强降水;低涡东移、锋面系统进一步增强了上升运动,触发形成锋面降水过程。2)较强的风垂直切变是"7·21"特大暴雨区别一般暴雨的另一个环境场特征。3)对流层中层西南引导气流加强、地面辐合线呈西南—东北向、云团移向前方存在上升运动中心、水汽通量辐合中心以及位势不稳定中心。这些因素造成对流云团在辐合线附近一个个生成,并向前方辐合和位势不稳定中心移动而形成"列车效应",造成特大暴雨灾害天气。4)地形对"7·21"暴雨存在迎风坡、喇叭口地形、地形中尺度辐合线等多种增幅作用,使得北京西南部山区成为对流云团的触发和加强区域。This paper is the second part of ＂Analysis on the cause of a torrential rain occurring in Beijing on 21 July 2012＂. The vertical mo- tion, wind vertical shear and terrain effect of this torrential rain have been investigated by using conventional observation data, intensive auto- matic weather station observations, Doppler-Radar data and 1°×1°NCEP reanalysis data. The conclusions are as follows. 1） The activities of the divergence in high-level jet, the wind shear line in low-level, the upward of the vertical circulation near low-level-jet, the convergence line of terrain and the terrain forcing jointly acted to trigger the intense upward movement, thus activated and maintained the convective pre- cipitation. The eastward movement of vortex and the frontal system further enhanced the vertical motion and the frontal precipitation. 2） The strong wind vertical shear was a unique environmental feature of the ＂7.21＂ event. 3） Factors, including the south-west-jet at mid-level, the southwest-northeast direction convergence line at surface level, the cloud clusters moving to the upward motion region, moist flux conver- gence region and the potential instability region, have resulted in a series of convective cloud clusters emerging, moving along the jet direc- tion, which acted as a ＂train effect＂, and lead to torrential rain weather. 4） The terrain played an important role in producing torrential rain. The windward slope, flared terrain and mesoscale convergence line make the mountain area in west-south Beijing become a region prone to form and enhance cloud clusters.

关 键 词：特大暴雨 列车效应 风垂直切变 地形 

分 类 号：P458.121.1[天文地球—大气科学及气象学]