福建一次秋季大范围暴雨成因分析

Analysis of a wide range autumn rainstorm in Fujian province

应用常规观测资料及NCEP再分析等资料,对2008年10月5—6日福建大范围暴雨成因进行诊断分析。结果表明:热带低压倒槽与冷空气共同作用使暴雨区低层气旋性辐合加强,上升运动加剧;差动温度平流增强斜压大气对称不稳定度;次级环流圈的形成和维持加大了降水强度并延长了降水持续时间;南海低层偏南气流为暴雨区输送了源源不断的水汽,同时也提供了动力和热力条件,对不稳定能量的积累、输送和释放起了关键作用;暴雨区层结不稳定维持较长时间,垂直风切变为对流系统的发展提供动能,造成对流系统斜压发展,激发位势不稳定能量释放;螺旋度在诊断低压中心位置、发展和移动的能力比垂直速度或涡度单一因子更好,但与降水中心位置存在滞后现象。

By using the conventional observation and NCEP reanalysis data, this paper studied the wide range rainstorm which took place in Fujian Province on Oct. 5 -6, 2008. It has been concluded that under the combined influence of the tropical depression trough and the cold air, low-level cyclonic convergence strengthened and the movement in the rainstorm area;the stronger vorticity adveetion at high- er-level can promote the ascending movement ; the stronger vertically differential adveetion of temperature results in the development of symmetric instability; generating and maintaining of longitudinal indirect secondary circulation promotes the intensity and duration of precipitation. The south currents at lower lev- els of the Southern China Sea provides water vapor continuously and creates the condition of dynamics and thermodynamics for the rainstorm area, at the same time it plays the key role in the progress of the unstable energy accumulating, transporting and releasing. Unstable stratification in rainstorm area maintained for a long time , and the vertical wind shear provided kinetic energy for the convection system development which is beneficial to the slantwise development of convection cells and inspired unsteady energy to release. The diagnosis ability of helicity in the tropical depression center, development and movement is better than the single factor of vertical velocity or vortieity, but it lagged behind the precipitation center.