中文摘要：

利用常规观测资料、卫星云图、雷达回波反演资料、自动气象站降水量以及NCEP/NCAR再分析资料,对2007年6月12—13日发生在华南西部的一次低涡切变特大暴雨过程的中尺度特征进行了分析,结果表明：（1）500 hPa高空槽经向度加大并东移南压,中低层低涡沿切变线东移,低空西南急流建立以及地面浅薄冷空气活动等天气系统相互作用触发了中尺度对流系统（MCS）的发展,造成暴雨。（2）地面降水时空分布具有明显的中尺度特征。大暴雨中心水平尺度都小于200 km,雨团持续时间5—7 h。（3）特大暴雨中心主要是由MCS移入造成的。柳江特大暴雨中心由两个MCS产生,一个沿低涡切变南侧的偏南气流移到暴雨中心上空;另一个沿切变线东移到暴雨中心上空。沿海暴雨中心则由一个MCS发展引发的。降水主要出现在MCS的中部冷云区内或云团边缘TBB梯度最大处。与MCS的生消过程对应,柳江暴雨区包含两次中尺度降水过程,第1次降水以热对流云团造成为主,第2次降水以低涡云系激发的MβCS产生强降雨为主;而沿海暴雨区是1次短时间持续性的MβCS强降水产生。暴雨主要由不断发展旺盛的对流单体引起,暴雨发生伴随着低空西南急流的建立,2—3 km高度上低空急流风速脉动增强了MCS的发展。（4）暴雨发生在高相当位温舌中,湿层厚度超过400 hPa,暴雨区层结具有位势不稳定或中性层结。（5）中尺度对流系统具有深厚的垂直环流结构,低层涡度柱在暴雨发生过程明显抬升,增强低层水汽辐合,锋区的动力强迫上升运动加强低层能量和水汽的往上输送,高层辐散气流增强MCS的发展。同时,暴雨区地形的作用增强了锋面强迫上升运动。

英文摘要：

Based on the conventional observational data,satellite images,retrieval data of radar echo,automatic observational precipitation and NCEP/NCAR reanalysis data,the mesoscale features of an excessive rainfall triggered by low-vortex shear in the western part of South China on 12-13 June 2007 were analyzed.The major conclusions are as follow：（1） the conventional observational data analysis indicated that the rainstorm event occurred under favorite synoptic conditions,which was closely related with activities of some synoptic systems,including the upper-level trough at 500 hPa east of Tibet Plateau being enlarged longitudinally and moving quickly southeastwards,the low vortex at 850 hPa moving eastwards along the shear line,the developing of the southwest jet on lower levels,and shallow cold air movement on the ground with their interaction causing a favorable circulation and motivating the mesoscale convective system development;（2） in the whole process of rainstorm event,the surface rainfall obviously showed meso-scale spatial and temporal distribution features with the horizontal scale of precipitation centers less than 200 km and the duration of approximate 5-7 hours which is distinguished from meso-β-scale features;（3）the mesoscale convective system invasion was the pivotal cause of the severe torrential rainstorm：the center of the severe torrential rainstorm in Liujiang was composed of two developing MCS clusters,one of them generated in afternoon and moved northeastwards to the place over the rainstorm center along the southwest air flow,and the another cluster occured on the western side of the shear line and moved eastwards to the place over the rainstorm center along the shear line,but the rainstorm center in the coastal area was triggered and developed by a single MCS cloud cluster;the precipitation emerged mainly in the central cloud cluster area or edge of MCS with the cloud brightness temperature less than -52℃and the black boby temperature（TBB） gradient maximized;corresponding to