利用风廓线雷达对广东前汛期短时强降水类暴雨过程低空风场特征的研究

A STUDY ON LOW-LEVEL WIND FIELD CHARACTERISTICS OF RAINSTORM CONTAINING SHORT-RANGE HEAVY RAINFALL DURING APRIL TO JUNE RAINY SEASON IN GUANGDONG BY WIND PROFILER DATA

为了更加深入地了解暴雨中尺度系统,利用风廓线雷达资料,对2012-2014年发生在广东前汛期的短时强降水的暴雨过程临近时次的低空急流强度、低空急流高度、低空急流指数以及各层垂直风切变等物理量进行了分析研究。研究结果表明:(1)在广东前汛期,86%的暴雨过程都会有短时强降水的出现;(2)2 km高度以下最大风速呈正态分布特征,主要集中在10~21 m/s之间,60%以上的强降水发生前3小时低空急流便已经存在,且随着强降水的临近,低空急流的比例逐渐增大,超过80%的过程强降水出现时有低空急流相配合;(3)暴雨发生前低空急流强度基本维持,最低高度逐渐降低。强降水出现时次,低空急流表现出逐渐加强的特征,最低高度也明显下降,从而导致低空急流指数I增大;(4)地面到不同等压面的垂直风切变随着高度的增加而逐渐减小,其中强降水发生时地面到925 hPa垂直风切变相较于暴雨发生前有所增大,而地面到850 hPa及700 hPa垂直风切变在强降水发生时则表现出下降的特征;(5)选取暴雨发生前各类物理量的中值作为暴雨发生的阈值,则低空急流强度在13.5 m/s左右,最低高度为1 km左右,低空急流指数I为6×10^-3s^-1左右,地面到925hPa、850 hPa以及700 hPa之间的垂直风切变分别在7.3×10^-3s^-1、6×10^-3s^-1以及4×10^-3s^-1左右。

By using the wind-profiler data from 2012 to 2014,the mesoscale weather system characteristics of rainstorms containing short-range heavy rainfall which occurred during April to June rainy season in Guangdong are studied.First,it is indicated that 86%rainstorms which occurred during the period from April to June in Guangdong are accompanied by short-range heavy rainfall.Second,the maximum wind speed below 2 km height is distributed normally,mainly concentrated in the range of 10-21 m/s.Low-level jets already exist 3 hours prior to the occurrence of more than 60%short-range heavy rainfall,and the proportion increases gradually with the approach of heavy rainfall.Third,before the rainstorm,the intensity of low-level jets generally maintains,and the lowest height gradually decreases.When short-range heavy rainfall occurs,the low-level jet gradually enhances,and the lowest height also decreases significantly,leading to a noticeable increase in the low-level jet Index I.Fourth,vertical wind shear from ground to different isobaric surfaces decreases with the increase of altitude.The vertical wind shear from ground to 925 hPa increases but decreases from ground to 850 hPa and 700 hPa,when short-range heavy rainfall occurs.Finally,the following pre-rainstorm median values of all kinds of physical quantities are selected as the threshold of rainstorm occurrence,13.5 m/s for the intensity of low-level jet,1 km for the lowest altitude,6×10-3 s-1 for the low-level jet Index I,and 7.3×10^-3 s^-1,6×10^-3 s^-1 and 4×10^-3 s^-1 for the vertical wind shear between surface to 925 hPa,850 hPa and 700 hPa,respectively.