中文摘要：

2008年7月6日20时—7日14时,高空低槽前云系产生了一条从广西南宁市到环江县东西宽约80km、南北长达350km的暴雨带,槽前云系南段一个中尺度对流系统在上林县产生了降雨量达265.0mm的特大暴雨。使用常规资料和FY-2C卫星云图、多普勒天气雷达和自动气象站等非常规观测资料进行分析。当高空槽移过青藏高原后,从卫星云图和等熵面分析图上可以检测到槽后有干空气东南下,干空气经云贵高原下沉到桂西和越南北部后,在槽底附近转折向东侵入到桂中,在上林县附近形成一个中尺度涡旋和中尺度负变压中心,中尺度对流系统在中尺度涡旋及中尺度负变压中心上空发生、发展并产生了强降雨,而中尺度涡旋和中尺度负变压中心的出现超前于强降雨约2h。研究表明,中尺度对流系统发生、发展的有利条件是：（1）槽前偏南暖湿气流向桂中暴雨区输送充足的水汽并形成了位势不稳定,为中尺度对流系统的发生发展提供了环境条件;（2）在上林县附近形成的中尺度涡旋辐合上升运动抬升暖湿气流触发对流而形成了中尺度对流系统;（3）对流单体沿低空切变线传播发展并入中尺度对流系统,使中尺度对流系统得以发展和维持。给出了中尺度对流系统发生发展机制的二维概念模型。

英文摘要：

A rainstorm belt of about 80 km and 350 km in the EW and NS direction respectively was generated by a cloud system in front of the upper-level trough from 20：00 BT 6 July to 14：00 BT 7 July 2008,covering from Nanning city to Huanjiang county,Guangxi Province,China.A mesoscale convective system（MCS） in the south of the cloud system triggered a torrential rain with precipitation of 265.0 mm in Shanglin county.The FY-2C cloud images,radar observations,records obtained from automatic weather stations and other irregular observations were used to analysis this process.Based on the cloud image and isentropic analysis charts,the dry air moved down across the Yunnan-Kweichow plateau to the west of Guangxi Province and the north of Vietnam after the upper-level trough passed the Tibet plateau,and it turned eastwards at the upper-level trough bottom to the middle of Guangxi,and then formed a mesoscale vortex and a mesoscale katallobaric center near Shanglin county.After that the MCS developped and generated heavy rain in the mesoscale vortex and katallobaric center.The severe rainfall occurred 2 hours after the mesoscale vortex and katallobaric center occurrence.The results show that the main favorable factors generating the MCS are as follows.Firstly,the sufficient water vapor was transported by the warm and wet southerly flow ahead of the upper-level trough to the middle of Guangxi to form the unstable potential,which provided an advantageous environmental condition for the MCS generation.Secondly,the MCS was generated while the warm and wet airflow was uplifted by the convergence and the ascend motion of the mesoscale vortex.Thirdly,convective cells moved forward along the low level shear line,which made the MCS maintain and develop.Furthermore,a 2D conceptual model of the MCS development mechanism is presented.