安徽一次大范围暴雨和大风过程的成因分析

对2010年6月8日08时—9日08时发生在安徽麦收区的一次大范围暴雨和大风过程进行天气学分析,分析结果表明:在低层辐合、高层辐散的有利环流配置条件下,高压的阻挡、低空西南急流和低空东风急流是形成这次暴雨的最主要原因。高压阻挡使降雨维持的时间较长,两支低空急流不仅为暴雨区提供了充沛的水汽,而且两者之间的相互作用使得降雨进一步增强。通过对低空东风急流的作用做深入分析发现:低空东风急流的存在不仅使低空西南急流输送的水汽在其左侧累积,而且低空东风急流上的正涡度平流也迫使江淮气旋向麦收区方向缓慢移动,并使其不断发展,进一步加大了江淮气旋移动前方的气压梯度,使风力加大,东风急流进一步加强,形成正反馈机制。另外东风急流的动量下传又使得地面出现偏东大风。

Analysis on a case of wide-range rainstorm and gale process in Anhui province

A wide range rainstorm and gale case occurred in wheat harvest areas of Anhui province on June 8 and 9, 2010 was analyzed in this paper. The results indicated that under the favorable conditions of circulation configuration between low-level convergence and upper-level divergence, the high-pressure blocking, southwest and easterly low-level jet were the main reasons for this rainstorm. The rain lasted for a long time due to the high-pressure blocking, and abundant water vapour was provided by the two low-level jets for the rainstorm, it was their interaction that further enhanced the precipitation. According to the comprehensive analysis, the existence of easterly low-level jet led to the water vapor transportation by southwest jet and the accumulation on its left side, and the positive vorticity advection on the easterly low level jet made the Jianghuai cyclone developing through the slow-moving process towards the wheat area, which further increased the pressure gradient in front of the Jianghuai cyclone, and the geostrophic wind increased while the easterly low-level jet was further strengthened, therefore the positive feedback mechanism was set up. Furthermore, the downward momentum transfer of easterly low-level jet caused the easterly ground gale.