引发暴雨的西南低涡特征分析

Feature Analysis on Southwest Vortex of Triggering Rainstorm

利用NCEP1°×1°再分析资料、逐时卫星云图资料和自动站资料,分析了与4次暴雨过程密切相关的中尺度系统西南低涡。结果表明,引发暴雨的西南低涡相对于环境场是湿涡,南边界是主要水汽输送方向。在西南低涡形成阶段,整层均为正涡度,一般维持深厚的上升气流,具有较为深厚的暖心结构。在其发展旺盛阶段,正涡度呈上升趋势,对流层中低层转为冷心结构,中高层则以暖心结构为主。当西南低涡在原地反复生消或长时间维续,高低层低涡中心位置趋于垂直且移速缓慢时,对流单体通常独立于上游斜压系统发展成中尺度对流辐合体或接近于中尺度对流辐合体的中尺度对流云团系统;当低涡中心移动较快时,对流单体发展不旺盛,通常并入上游斜压云系且向东移。

Using NCEP reanalysis data,conventional observation data,hourly satellite image and automatic station data,the characteristic of mesoscale system-southwest vortex are analyzed,which is closely related to four rainstorm processes.The results show that：（1） The southwest vortex that triggered heavy rainstorm is wet vortex relatived to the environmental field,the south boundary is the main direction of moisture transport.In the formation stage of southwest vortex,the whole levels are positive vorticity,and generally keep deep updraft,and have a deep warm-cored structure.In the strong development stage of southwest vortex,the positive vorticity is rising,the lower-level of the tropospher change to cold-cored structure,and its upper-level is warm-cored structure mainly.（2） When the southwest vortex repeatedly generat and disappear in situ or last longer,vortex centers in the upper-and lower-level are tend to vertical and its speed is slow,the convective cells are usually independent of the upstream baroclinic system and develop into MCC or MCS closed to MCC.When the southwest vortex center quickly move,the convective cells weakly develop and often incorporate into the upstream baroclinic cloud system eastward.