2017年湖南一次极端降雨过程特征及成因分析

Characteristics and Causes Analysis of Extreme Rainfall Event in 2017 in Hunan Province

2017年6月22日—7月2日湖南出现了一次罕见的大范围持续暴雨、大暴雨过程,持续强降雨造成了重大人员伤亡和财产损失。利用地面常规探测资料、自动站资料和NCEP/NCAR再分析资料,对此次极端降雨过程的成因进行了分析。结果表明:(1)过程发生在单阻型稳定背景条件下,西太平洋副高较常年位置偏南,带状副高与北方冷涡对峙,导致梅雨锋雨带在湖南摆动;(2)高低空急流加强了低层辐合高空辐散的动力作用,同时高能高湿激发对流不稳定,为大暴雨产生提供了动、热力条件;(3)水汽异常偏高,整层可降水量超过常年同期1~2个标准差,其大值区的演变与实际强降水区域对应较好;(4)湖南地形对降水有一定的增幅作用,地形坡度绝对值与降水量变化十分吻合,地形变化越剧烈降水强度越大,且在地形复杂的2个山峰之间区域通常对应着降水的峰值。

An extremely severe precipitation event appeared in Hunan from June 22th to July 2th,2017.The extreme rainfall brought heavy casualties and property losses.Based on the routine surface observation,automatic stations data and NCEP/NCAR reanalysis data,the the synoptic cause of the extreme rainfall was analyzed.The results showed that:(1)the subtropical high in the Western Pacific Ocean was farther south than normal,and the zonal subtropical high confronted with the cold vortex in the north,which leaded to the oscillation of the Meiyu front rain belt in Hunan.(2)The effect of high and low jet streams enhanced the dynamic effect.The high energy and humidity inspired the generation of convection instability.They provided dynamic and thermodynamic conditions for the heavy rainstorm.(3)Vertically integrated precipitable water exceeded 1-2 standard deviations during the same period over the years,and the evolution of the large value region corresponded well to the actual heavy precipitation area.(4)The terrain of Hunan has a certain increasing effect on the precipitation.The absolute value of topographic slope coincided with the change of precipitation.The more severe the topographic change,the greater the intensity of precipitation.The region between two complex terrain usually corresponded to the peak of precipitation.