2011年湖南一次强暴雨过程中尺度分析

Meso-scale analysis on a heavy rainfall event in Hunan province during 2011

以LAPS局地分析资料为主,综合利用卫星云图、地面自动站资料和NCEP提供的全球分析资料,对2011年6月9—10日湖南一次特大暴雨过程进行了分析,结果表明:降水主要发生在对流云团中亮温TBB<-70℃的区域的偏西一侧,在TBB<-80℃的区域内降水最强;锋前暖区中的对流云团,在中低层是以条件不稳定机制为主的垂直上升运动,而在中高层,是以条件对称不稳定机制为主的垂直上升运动。中尺度对流系统在不断东移南压的过程中,受高层的辐散性流场的抽吸作用和低层的对流不稳定而发展加强。强气旋性切变和正涡度平流触发中尺度气旋发生、发展,β中尺度涡旋是此次特大暴雨过程的直接影响系统。对整层的高度场和流场进行滤波分析发现,此次暴雨过程中的中尺度气旋活跃,强降水雨团与中尺度低层辐合、高层辐散中心基本重合。利用高(低)层中尺度辐散(合)中心位置确定暴雨中心有一定的预报指导作用。

Using satellite cloud data, unconventional automatic observations, FNL and LAPS global analysis data provided by NCEP the evolution characteristics of the meso-scale system and the cause of a heavy rain event occurred in Wunan on 9-10 June, 2011, were analyzed through Barness band pass fil- ter. Results show that the rainfall occurs mainly in the west of the convective clouds with TBB 〈-70 ℃, and that in the area of the TBB〈-80℃, the heaviest rain is available. The formation and development mechanism of the meso-scale convective system（MCS） in prefrontal warm area can be considered to be vertical upward motion characterized by conditional instability at the middle and lower levels, while at the upper level, it is characterized by conditional symmetrical instability. In the process of moving to thesoutheast, the MCS is strengthened by the pumping function of the divergence flow at the high level and by the convective instability at the low level. The B-scale vortex triggered by strong cyclonic shear and positive vorticity advection directly impact the rain process. The filtering analysis on the geographical height and stream at 900 hPa and 200 hPa shows that meso-scale vortexes are active in this process. The highly coincidence of meso-scale convergence center and the meso-scale rain cell indicates that it is abso- lutely important to determine the rainfall center with the help of low level meso-scale convergence center.