Statistical Analysis And Simulation Diagnostic Study Of Vortex Rainstorm In Hebei Province

With statistical and synthetic analysis on the examples of low eddies rainstorm weathers between 1991-2000 of Hebei Province, it is indicated that the low eddies system of rainstorm is primarily for the Northwest eddies, to the next is for east-Mongolia cold eddies, the influence of southwest eddies is lighted. Northwest eddies affect mostly at south department of Taihang mountain, and east-Mongolia cold eddies primarily affect at Yanshan mountain southern foot, mostly at July and August. The southwest eddies rainstorm only take place in July. 70% of northwest eddies rainstorm accompany with typhoon or tropical cyclone at south. The vapour source is Yellow Sea or East China Sea in northwest vortex meridional circulation. And it is South China Sea or the Bay of Bengal in northwest vortex zonal circulation and east-Mongolia cold vortex meridional circulation. Midlatitude meridional circulations at 500hPa are advantageous to the rainstorm continuously and heavily. The general emergence of the rainstorm area is near the worm sheer line of low eddies, the left side of the biggest wind velocity area at 700hPa.By using MM5 model, numerical simulation is carried out for the rainstorm on 4th to 5th July, 2000.The result from diagnosis about moist potential vorticity and its tendency shows that, the vortex heavy rain usually locates the eastward part of high MPV center of vortex circulation in the lower troposphere, corresponding to the maximum negative region. It is advantage to the development of the vortex rainstorm that plus MPV zone just over minus one. The local variations of moist potential vorticity can indicate the locality of the heavy rain. Horizontal flow and vertial transportation of MPV play a important part in the varying of the heavy rain.The meco-scale disturbance field is analyzed. It is found that there are two periods through the development and spread of inertia-gravity wave. Meco-scale negative value center of vorticity and the positive value center of divergence spread towards northeast, and disappear later, corresponding with the rainfall center spreadtowards northeast twice and return to south. So, inertia-gravity wave spreading towards northeast and maintaining in south is the important reason of rainfall region moving and continuously in south.Though analysis convection instability condition, it shows that it is convection instability in the whole process of heavy rain. The rainfall appears latter the convection instability, and strengthen along with it. Rainfall region moves with it at the same time. Convection instability is the important mechanism for meco-scale rainfall continuously in the south of North China.