一次高原涡东移引发江淮强降水的动热力机制分析

Analysis of Dynamic and Thermal Mechanism of Heavy Precipitation over the Yangtze-Huaihe River Basin Caused by a Qinghai-Xizang Plateau Vortex Moving Eastward

利用ERA5(0.25°×0.25°)逐小时再分析资料,TRMM卫星降水资料和FY-2E卫星黑体亮温(TBB)资料等,探讨了2017年7月7-9日的一次移出高原涡形成发展的环流背景和移动特征,以及引发江淮流域强降水的动热力机制,并应用HYSPLIT4模式追踪江淮流域强降水的水汽源地。结果表明:此次高原涡生成于高原中部,先向东南方移动,到达四川中部后转为东北向移动,生命史为39 h。200 hPa南亚高压和高空急流强度较强,低涡位于高空急流入口区右侧的辐散区,促使低涡形成和发展。500 hPa低涡前部的负变高中心以及西太平洋副热带高压边缘的西南气流引导低涡的东移和转向。低涡移出高原后处于高空槽前正涡度平流造成的减压区,加之大地形背风坡有利于气旋性涡度增强,低涡得以发展。低涡下高原后沿江淮切变线移动,槽后的冷空气与携带孟加拉湾和南海水汽的偏南气流汇合,在锋生作用下低涡发展为江淮气旋,降雨量迅速增强达到大暴雨标准。高低空急流的耦合和低层对流不稳定的发展加强了动力抬升作用,有利于江淮强降水的形成。强降水的水汽源地主要为南海和孟加拉湾,降水最强时段对应辐合上升运动最强,对流云发展旺盛使降水得以维持。

Using ERA5(0.25°×0.25°)hourly reanalysis data,TRMM satellite precipitation data and FY-2E satellite black-body temperature(TBB)data,the circulation background and movement characteristics of the formation and development of a Qinghai-Xizang Plateau vortex(QXPV)moving out of the Tibetan Plateau from July 7 to July 9,2017,as well as the dynamical and thermal mechanism of the heavy precipitation in the Yangtze-Huaihe River Basin were discussed,and the HYSPLIT4 model was used to track the water vapor source of the heavy precipitation in the Yangtze-Huaihe River Basin.The results show as follow:The QXPV was generated in the central part of the Tibetan Plateau,first moved to the southeast and then to the northeast after reaching the central part of Sichuan,with the life history of 39 h.At 200 hPa,the South Asian High and the upper-level jet stream were strong,and the vortex was located in the divergence region on the right side of the upper-level jet inlet area,which promoted the formation and development of the QXPV.The negative height center in the front of the vortex and the southwest airflow at the edge of the West Pacific Subtropical High lead the eastward movement and turn of the QXPV at 500 hPa.After the QXPV moved out of the Qinghai-Xizang Plateau,it was in the decompression area caused by positive vorticity advection in front of the high trough.In addition,the leeward slope of the large terrain was conducive to the enhancement of cyclonic vorticity,so the QXPV developed.The QXPV moved along the Yangtze-Huaihe shear line after it moved out of the Tibetan Plateau,and the cold air behind the trough merged with the southerly airflow carrying water vapor from the Bay of Bengal and the South China Sea.Under the action of frontogenesis,the QXPV developed into a Yangtze-Huaihe cyclone,and the rainfall rapidly increased to the standard of heavy rain.The coupling of upper-level jet and low-level jet,and the development of low-level convective instability strengthened the dynamic uplift,which was conducive to the formation of heavy precipitation over the Yangtze-Huaihe River Basin.The water vapor source of heavy precipitation was mainly the South China Sea and the Bay of Bengal.The convergence upward movement was the strongest during the period of the strongest precipitation,and the convective clouds developed vigorously to maintain the precipitation.