内蒙古一次暴雨过程中尺度特征及成因分析

Mesoscale Characteristics of a Rainstorm Process in Inner Mongolia and Its Cause Analysis

利用常规观测资料、NCEP 1°×1°再分析资料、自动气象站资料、FY-2E逐时云顶亮温TBB资料和闪电定位资料,对2013年7月14-16日内蒙古暴雨过程进行分析。结果表明,此次暴雨过程58%的暴雨站点在2 h、3 h或6 h即达到暴雨量级,强降水造成的中尺度雨团和中尺度雨带是暴雨主要表现特征。强降水是冷锋云系或涡旋云系中不断生消的中尺度对流系统（MCS）直接造成的,在MCS发展和成熟阶段,雨团和地闪密度大值区位于TBB≤-52℃冷云区冷空气流入一侧,但MCS移出区域,也有雨团的出现,是由层状云引发的。地闪密度增加,MCS发展,雨强增强,地闪频次锐减,MCS开始消亡,雨强减弱。阻塞形势稳定、南亚高压东伸和西太平洋副热带高压位置偏北是MCS发生的有利行星尺度背景条件,低空急流日变化是造成强降水集中出现在前半夜至凌晨的主要原因。对流层低层高温高湿、位势不稳定层结和风垂直切变对MCS形成提供了有利环境场。地面中尺度＂人＂字形切变线形成的扰动机制先于MCS发生,MCS出现在暖式切变线南侧不稳定区,但对流层高层强辐散中心和低层强正涡度中心滞后于强降水峰值出现时刻3~4 h。

Using conventional observational data,NCEP 1°×1° reanalysis data,automatic weather station data,FY- 2E hourly Temperature of Black Body（TBB）data and Cloud- to- Ground（CG）lightning data,a rainstorm process was analyzed in Inner Mongolia from 14 to 16 July 2013. The results showed：The rainstorm stations about 58% could reach rainstorm magnitude in 2 hours,3 hours or 6 hours,mesoscale rain cluster and mesoscale rain belt were important feature of rainstorm process. Heavy rainfall was caused by mesoscale convective system（MCS）that generated and vanished in cold front clouds and vortex clouds. When MCS was developing and matured,rain cluster and maximum value of CG density were located the coldest of TBB≤- 52 ℃ where the cold air flowed into. But the region where MCS shifted out existed rain cluster caused by stratiform clouds. When CG density increased,MCS developed and precipitation intensified. When CG density decreased,MCS dissipated and precipitation weakened. The blocking maintenance,the eastward extension of South Asia High and the northward position of the West Pacific Subtropical High provided planetary- scale circulation feature for MCS.The main reason that heavy rainfall concentrated form midnight to dawn was caused by diurnal variation of lowlevel jet. It was useful for persistent and development of MCS that there were high temperature and high moisture,geopotential instability layer and vertical wind shear in low- level of troposphere. Disturbance mechanism completed by the surface mesoscale‘people＇-shaded shear line advanced development of MCS. MCS occurred in the area of instability on the south side of warm shear line,but an upper-level divergent center and a low-level positive vorticity advection center lagged peak value of heavy rainfall approximately 3~4 hours.