一次强暴雨过程地闪活动特征与中尺度对流系统和强降水的关系

Characteristics of Ground Lightning and Relationships of Mesoscale Convective Systems and Heavy Rainfall in a Strong Rainstrom

利用2007年8月8日18时至9日02时发生在陕西关中强暴雨期间的地闪、卫星TBB、雷达回波和地面加密降水资料,通过统计和对比分析的方法,分析了地闪活动特征及其与中尺度对流系统(MCS)和强降水的关系。地闪活动特征分析显示,暴雨过程中负地闪占绝对优势,为总地闪的97.7%。负闪频数和总闪频数的逐时演变趋势完全一致且呈现两峰一谷的趋势,正闪频数的变化呈现三峰两谷的趋势,但是正闪频数最大值与总闪、负闪频数峰值时间一致。负闪活跃期正负闪6 min演变均表现为多峰结构,正闪的波峰提前于负闪的波峰12 min。负闪频数变化和MCS、雷达反射率因子演变对比分析表明,负闪发生区是未来对流云团和对流发展加强区,负闪频数密集区位于对流云团前部TBB等值线密集区,负闪频数的急剧增加意味着未来对流系统的猛烈发展;负闪主要出现在回波强度大于40 dBz的区域,正闪则落到强回波中心两侧30～40 dBz的回波区,中尺度对流系统快速发展加强期,负闪密集区位于回波单体的前沿,中尺度系统发展稳定少动期,负闪大部分集中在各对流单体的强回波中心附近。对比分析地闪与暴雨发生发展的关系可见,地闪的发生和急剧增加对暴雨发生和发展加强有很好指示意义,初闪的发生提前于强降水发生,地闪急剧增加与降水强度猛增密切关联,负地闪发生密集区是未来强降水发生区。

Based on the observation data of the lightning location system,temperature of blackbody brightness, Doppler radar echo and denser surface precipitation measurements from the process of a heavy rainstorm during 8~9 August 2007 in the Central Shaanxi Plain,the characteristics of ground lightning,and relationships of ground lightning,MCS,and rainstorm intensity are analyzed separately.The results indicate that the negative ground lightning accounts for the 97.7 percent of the total ground lightning.Hourly evolution tendency of negative ground lightning frequency and total ground lightning frequency presents a two-peak one-valley structure.Positive flash frequency changes have a tri-peak two-valley trend.The ground lightning frequency of 6 min positive and negative flashes in the active negative lightning period displays a trend of multi-peak value.The peaks of positive ground lightning frequency is 12 min prior to negative ground lightning frequency peaks.The relationship of ground lightning and MCS shows that the negative ground lightning happening area is the convective cloud cluster development and strengthening area in the future.The densified locality of negative ground lightning frequency is situated in the concentrated TBB isoline area in front of the convective cloud cluster.The sharp increase of negative ground lightning frequency means MCS development by-and-by.Negative flash occurred mainly in the echo area whose strength is greater than 40 dBz,and positive lightning falls into both sides of strong echo center. During the rapid development of MCS,negative flash dense area is located in the forefront of single echo. In MCS stabilization period,negative flashes are concentrated near the center of the strong echo.The evolution relationship between the ground lightning and the heavy precipitation reveals that the occurrence and sharp growth of the ground lightning have very good indicative significance to the development and strengthening of the rainstorm.The occurrence of the first flash occurs ahead of the strong precipitation happening.The sharp increase of ground lightning has a close connection with the sudden increase of precipitation intensity.And the concentrated regions of the negative ground lightning may indicate the area where strong precipitation happens.