西安市一次雷暴过程的闪电活动特征

Characteristics of the Lightning Activity During a Thunderstorm Process in Xi’an

利用陕西省闪电定位数据、多普勒天气雷达资料及逐小时降水资料,分析2018年8月9日西安市一次雷暴过程中闪电与降水、雷达回波和气流切变的关系特征,并进行特征对比分析。结果表明:15:00左右初始闪电发生后,闪电频次逐渐增加,17:54达到最大峰值后,闪电频次逐渐减少。整个雷暴过程中,正地闪占比较高,为23.8%;闪电频次出现了2次明显峰值,最大闪电频次为124次/6min,出现时段为17:48-17:54。闪电主要集中在强降水发生区域和时段,且先有闪电活动后有降水发生,正地闪活动与降水有密切关系。60 dBZ以上反射率面积与闪电频次随时间变化趋势一致,65 dBZ强反射率的出现和消失伴随着闪电频次的增加和减少。闪电频次与50 dBZ和40 dBZ的反射率等值线变化有较好的对应关系。正、负地闪在不同反射率范围集中程度不同,正地闪主要活动在强回波区前部和后部,且主要发生在雷暴云发展成熟后,负地闪则集中在强回波区中部和后部。地闪发生区域与上升气流和风切变区域有密切关系,但并不完全发生在上升气流区,负地闪在上升气流和下沉气流区的占比,对对流系统发展阶段有一定指示作用。经过特征对比分析,3次雷暴过程中降水量与正地闪的相关性、闪电与雷达反射率的关系均与西安市雷暴过程有相似特征。

Based on lightning location data of Shaanxi Province,Doppler radar data and hourly precipitation data,this paper analyzes the relation characteristics among lightning,precipitation,radar echo,and airflow shear during a thunderstorm process in Xi’an on August 9,2018,and conducts a comparative analysis of the characteristics.The results show that the frequency of lightning increased gradually after the initial lightning occurred at about 15:00,and decreased gradually after the highest lightning frequency at 17:54.In the whole thunderstorm process,the proportion of positive CG(Cloud-to-Ground)flashes is higher,accounting for 23.8%.There were two obvious peak values of lightning frequency,with the highest frequency of 124 times in 6 min from 17:48 to17:54.The lightning was mainly concentrated in the area and time period of heavy precipitation.Lightning activity occurred before the precipitation,and positive CG flashes was closely related to precipitation.The reflectance area above 60 dBZ was consistent with the lightning frequency over time.The appearance and disappearance of 65 dBZ strong reflectance were accompanied by the increase and decrease of lightning frequency.At the same time,there was a good correspondence between lightning frequency and the reflectance contours of 50 dBZ and 40 dBZ.Positive and negative CG flashes had different concentration degrees in different reflectance ranges.The positive CG flashes were active in the front and rear parts of the strong echo zone and mainly occurred after the developed thunderstorm clouds,while the negative CG flashes were mainly concentrated in the central and rear parts of the strong echo zone.The occurrence area of CG flashes was closely related to the updraft and wind shear area,but it did not occur entirely in the updraft area.The proportion of negative CG flashes in the updraft and downdraft areas had a certain indication for the developing stage of convective system.The above comparative analyses suggest that the correlation between precipitation and positive ground flashes,as well as the relationship between lightning and radar reflectivity in three thunderstorm events have similar features with those of the thunderstorms in Xi’an.