The Genesis of Extreme Heavy Rainfall Event on the Steep Terrain of Eastern Qinghai-Xizang Plateau

Based on NCEP 1°×1°reanalyzed data,Sichuan meteorological observation stations data and satellite data,the extreme continuous heavy rainfall event along the Longmen mountains in northwest Sichuan basin on Aug 16th to 18th,2012 was analyzed.The heavy rain event on the steep terrain of eastern Qinghai-Xizang Plateau with prominent geographical characteristics.The trigger mechanism and topographic forcing were evaluated.The result of the study indicated that this strongly convective weather process was aroused by eastward moving plateau shear line.It was in advantaged large circumfluence background of the subtropical anticyclone remained stable before the rainstorm.There was wind direction and velocity convergence at low-level in the heavy rainfall region.Northeast-southwest direction the Longmen mountains with that of the steep terrain on the east side of Qinghai-Xizang Plateau leading strong ascending motion.The strongest updraft movement occurred in the convergence area of the vertical shear of east and west wind the most significant thermal characteristics is high temperature and humidity at low-level and atmospheric instability stratification.The cold advection in the upper air and the warm advection in the lower level and the dry advection in the upper air and the wet advection in the lower level cause the strong convection weather.