高原低涡影响下的一次暖区强降水特征分析

ANALYSES OF HEAVY RAINSTORM IN WARM SECTOR UNDER THE INFLUENCE OF THE LOW-PRESSURE SYSTEM OF QINGHAI-XIZANG PLATEAU

利用地面和高空观测资料、雷达资料、FY-2E逐时云顶亮温TBB资料以及NCEP/NCAR(1°×1°)再分析资料等,对2014年7月30—31日四川盆地的暴雨天气过程的中尺度对流系统特征及触发机制进行分析和探讨。结果表明:(1)本次暴雨的地面中尺度风场辐合线与强降水落区有较好的对应关系,辐合线比强降水提前1 h出现,且强降水落区主要位于辐合线左侧有边界层弱冷空气影响的偏北气流范围内,同时强降水落区随地面中尺度风场辐合线移动;(2)暴雨过程临近时具有不稳定能量特别高、地面和低层露点温度大、抬升凝结高度低、湿层非常深厚等显著特征十分有利于强降水的发生,降水过程中有充足的水汽向暴雨区输送并在暴雨区有明显的辐合上升,为强降水的持续提供了较好的条件;(3)在高原低涡缓慢东移过程中,涡前的正涡度平流使低层涡度增加、垂直上升运动加强,触发强对流活动,是本次暴雨过程的触发机制之一;强对流降水造成的非绝热加热正反馈于大气,使强对流活动发展,强降水天气持续,是本次暴雨过程的维持机制之一。

An analysis of the meso-convective system in a heavy rain event on 30 to 31 July 2014 in the Sichuan basin is performed by using routine observational data, ground intensive observational data, FY-2E satellite observational data, Doppler radar data and NCEP/NCAR1°×1°reanalysis data. （1） There is good correlation between the heavy precipitation and the meso-scale convergence line （MCL）： the MCL occurred an hour earlier than the heavy precipitation, which was mainly within the weak cold air of the boundary layer on its left side of the MCL and moved with it. （2） High unstable energy, high low-level humidity, a low lifting condensation level and a deep wet layer were very beneficial to the occurrence of the heavy rain. And adequate water vapor is transported to the heavy rain area and then provided good moisture conditions for the maintenance of the heavy rain. （3） The positive vorticity advection made the low-level low-pressure develop and vertical movement strengthen, and triggered convective activity in the eastward-going process of the plateau vortex, which was the exciting mechanism of heavy rainfall. And the diabatic heating released by rainfall condensation played a feedback role in the maintenance of the heavy rain.