Comparative Study On Orographic Influence Between Yangtze River And Huaihe River Basin Mei-yu Rainstorm

In this paper, by using Micaps data, reanalyzed data from NCEP/NCAR and TRMM data, two typically Meiyu rainstorms which occurred over the lower and middle reaches of Yangtze River basin during3～4Jul2011and occurred over the Huaihe River basin during23～24June2011are studied. With the4times daily1°*1°NCEP global grid data, the two rainstorms are fully simulated by the mesoscale numerical model WRFV3.2, which can be proved by contrasting simulated data and observation dataThree sensitivity experiments are designed to analysis the effect that the terrain of Dabieshan on the rainstorm. The simulated data and sensitivity experiments are analysised, result shows as follow:(1) The terrain of Dabieshan area could promote the precipitation on west and middle Anhui Province, and the range of rainfall center would increase and shift eastward with a increased terrain of Dabieshan area.(2) If the terrain of Dabieshan area increased, the meso-scale troughs and ridges could be greatly strengthened and the convergence would be more severe. When the convergence zone is over the lower and middle reaches of Yangtze River basin, the eastward moving speed of vapor inverse correlation to the height of terrain, the rainstorm form easier over the area near Dabieshan and the maximum value of precipitation will decrease over the south area of Jiangsu Province where is further to Dabieshan. If the convergence zone locates over the Huaihe River basin, the intensity of high moisture convergence area which will be weakening on its eastward-transition has a positive correlation with the height of Terrain. When the terrain of Dabieshan area decreased or disappeared, the rainfall center at Huaihe River basin would shift eastward apparently.(3) Rain storm always occurs in unstable layer, when the unstable layer being damaged, unstable energy release violently, and heavy rain falls. When the rainfall occurs over lower and middle reaches of Yangtze River basin, the terrain of the Dabieshan terrain forced the southwest airflow uplift, inspire disturbance trough and ridge, the higher the terrain, the more violent the unstable energy released, and the higher terrain could reduce energy releasing violently in further area. When the rainfall occurs over Huaihe River basin, sufficient moisture and terrain disturbance trough and ridge lead to the breakthrough of unstable stratification, which would lead to intense energy release process and short-range severe precipitation.(4) Based on both dynamic and thermodynamic factors, the Dabieshan terrain could decrease the development of potential vorticity anomaly over Yangtze River basin, relatively flat upper reaches terrain height is beneficial to development of potential vorticity anomaly in southern area of Jiangsu province. Nevertheless, over the Huaihe River basin, a positive feedback exist between the Dabieshan terrain and precipitation, if there has no terrain of Dabieshan, no violent convection weather will occur.