一次沿川西高原东麓地带的强降雨过程分析

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

利用NCEP1°×1°再分析资料和地面加密自动站资料及卫星资料,对2012年8月16～18日盆地西北部沿龙门山脉的连续特大暴雨的形成机制进行探讨,此次暴雨过程出现在青藏高原东侧陡峭地形向盆地的过渡带,具有突出的地域特点。重点分析了青藏高原切变线东移期间,副高西北侧暴雨区内的对流触发机制和地形作用。分析表明:副热带高压前期的维持稳定与高原低值系统东移是产生强降雨的环流背景,在强降雨区域低层具有明显的风速风向辐合,东北—西南向的龙门山带即青藏高原东侧陡峭地形引起了盆地低层东南气流强烈的垂直上升运动。青藏高原东侧暴雨区最显著的热力特征是低层具有明显的高温高湿和大气不稳定层结。此次强降雨具有典型的"上干下湿,上冷下暖"的结构,正是强对流天气形成的有利条件。

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 char- acteristics. 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 back- ground 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 on the east side of Qinghai - Xizang Plateau leading - southwest direction the Longmen mountains with that of the steep terrain 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 the lower level and the dry weather. atmospheric instability stratification. The cold advection in the upper air and the warm advection in advection in the upper air and the wet advection in the lower level cause the strong convection