梅雨锋降水运动诊断分析与(大)暴雨形成——江淮梅雨锋暴雨的天气学成因个例分析

Diagnose of Precipitation Motion for Studying Heavy Rain Formation:Synoptic Cause Analysis of a Meiyu-Front Rainstorm

对T213 L31再分析模式大气,在等熵坐标系上对天气学大尺度凝结函数降水、水汽通量散度降水做了诊断计算;同时,对整层对流不稳定性降水和气块(团)湿不稳定降水做了理想设计与诊断计算。对2003年7月江淮梅雨锋暴雨的计算与分析表明:两种天气尺度波动的大尺度稳定性降水运动的降水量级较小,都不足以直接形成暴雨;而对流不稳定降水运动可以形成暴雨,却不足以形成大暴雨;只有气块不稳定降水运动,才是梅雨锋上大暴雨的自组织、正反馈的唯一降水机制。研究表明,该江淮梅雨锋暴雨虽然存在着明显的梅雨锋天气尺度降水系统,但充沛的水汽通量和异常高温高湿气团的维持,使得在梅雨锋上发生着的非等熵湿绝热运动及其对流不稳定降水和气块不稳定降水,是(大)暴雨发生的天气学成因。

The diagnose and calculation of synoptic large-scale condensation function precipitation and moisture flux divergence are conducted on the isentropic coordinates system with the re-analysis data of T213 L31 model atmosphere. Meanwhile, the ideal design and diagnostic analysis are made of the covection-unstable precipitation for the entire layer and the wet instability for air parcels （mass）. The calculation and analysis of the Meiyu-front heavy rainfall over the Changjiang-Huaihe region in July 2003 indicates that the rainfall amounts leading from both types of synoptic scale precipitation movements （condensation function and moisture flux divergence） are not large enough to form heavy rain ; the moist air-layer convective precipitation movement may induce heavy rain but not rain gust ;only the air-mass wet-instability precipitation movement is strong enough to cause the self-or- ganized and positive-feedback rain gust. It is made known that although there are above-mentioned two largescale precipitation movements on the Meiyu front in the Changjiang-Huaihe basin in July 2003, the highly moist air masses （precipitable water） maintain long time and transport rapidly, leading to the occurrence of non-isentropic saturation-adiabatic motions and the convection-unstable precipitation of the moist air layer and the airmass instability precipitation, which are the synoptic causes of the heavy rain event.