急流在梅雨期持续暴雨过程中的作用

Analysis about function of jet for the persistent Meiyu rainstorm

本文利用实况资料和客观分析资料,对造成江苏2010年7月9—14日的暴雨过程中高低空急流特点、配置及对暴雨的影响进行了分析。结果表明:高空动量下传,引起低空扰动加强,从而使得低空急流加强和维持。低层高能的平流为江苏境内暴雨和大暴雨的产生提供了充足的能量。低空西南风急流是暴雨产生的重要因子,仅在700 hPa出现强劲西南风急流,就可以导致江苏境内的强降水发生。分析还表明:阶段性暴雨起始的时候,暴雨落区上方都出现了负散度和正散度相互交错的情况,直至6 h后才有高空辐散低空辐合的典型形势。高低层急流配置和次级环流的维持为暴雨的持续提供了有利条件。

Using the observed data and the objective reanalysis data,this paper analyses the characteristics and coupling of the upper-level and the low-level jet streams which caused the rainfall in Jiangsu during 9 July to 14 July,2010 and the influence on the heavy rain.The results show that the upper momentum transers downward which enhances the low-level disturbance and then strengthens and maintains the low-level jets.The low-level southwest jet stream is the main factor of the rainstorm occurrence.Only the appearing of southwest jet stream at 700 hPa can bring about the heavy rain in Jiangsu.Analysis also shows that the alternating distributions of positive and negative divergences took place over the rainfall areas at the beginning of the rainstorm phase,which become the typical form of the upper-level divergence and the lower-level convergence after 6 h.The coupling of upper and lower jet streams and the maintenance of the secondary circulation offer the advantageous conditions for the persistence of rainfall.