2018年7月5日江淮暴雨发生发展机制的模拟及诊断

利用WRF中尺度模式对2018年7月5日江淮地区一次局地暴雨过程进行模拟,拟通过真实模拟降水过程降水落区、强度及大值中心等,深入分析此次暴雨及其中尺度系统的发生、发展机制。结果表明:高低空急流耦合、低层辐合高层辐散加之整层正涡管产生探至对流层顶的强烈上升运动为强降水及落区飑线系统的发生发展提供有利的动力条件;显著湿区、西南水汽输送与汇聚提供了充沛的水汽条件;假相当位温等温线在暴雨落区的密集分布提供了热力条件。湿位涡分析中,淮河流域的湿位涡正压部分(MPV1)低层负值、中层正值的形势使低层不稳定能量持续积蓄。湿位涡分析展现了本次江淮暴雨的特殊性:一是不稳定能量积蓄位置较低,二是对流系统发展区的东西两侧均处于相反值区域,在不稳定能量受到两侧稳定能量夹击时,系统发展剧烈,但趋于稳定的时间变快,使系统留存时间缩短;同时由于这样的牵制,系统移动较为缓慢,导致降水中心停留在苏皖一带,解释了本次江淮暴雨来势迅猛、降水集中的原因。

Numerical simulation and diagnostic analysis on the generation and development of rainstorm in Yangtze-Huaihe River basin on July 5,2018

A rainstorm occurred in Yangtze-Huaihe River basin on July 5, 2018, was simulated with the mesoscale model of Weather Research and Forecast (WRF). Results show that the location of the precipitation area, intensity, and large value centers successfully, which could describe the occurrence and development of the rainstorm and mesoscale system. The fine grid data output from the model was used for diagnostic analysis. Results indicate that the coupling of high and low air jets, the convergence of lower layer, the divergence of upper layer, and the strong ascending motion to the tropopause caused by the whole positive vorticity tube provide favorable dynamic conditions for the occurrence and development of heavy precipitation and squall line system in rainfall area. The significant wet region, the southwest moisture transport with convergence, the potential instability along with the high energy region provide the vapor and thermal conditions. The analysis of the moist potential vorticity shows the particularity of this rainstorm. One is the unstable atmosphere is mainly concentrated at low altitude. In addition, both barotropic part (MPV1) and baroclinic part of moist potential vorticity (MPV2) were stuck in the middle of low value regions on the east and west sides, which was the reason why the rainstorm developed violently and maintained a short time.