一次中尺度雷暴大风过程的闪电特征分析

Characteristics of Lightning Activity in a Thunderstorm with Damaging Straight-Line Wind

2005年6月21日山东北部出现了一次中尺度对流系统,并伴有地面灾害性大风。作者综合闪电定位资料、雷达和卫星资料详细分析了这次中尺度对流系统的闪电活动特征,结果表明,在系统初始发展阶段地闪频数快速增加.成熟阶段地闪频数一直较高,且都在20次/5 min以上,在减弱消散阶段,正地闪比例超过负地闪。负地闪多发生在对流降水区,而正地闪则对应于稳定的层状云降水区。逐小时地闪次数峰值滞后于云顶最低温度峰值,小于-50℃的冷云覆盖面积峰值滞后于地闪次数峰值。这次地面大风主要是较强下沉气流底部外流造成的,利用WINDEX计算的地面最大风速潜势与观测的阵风值非常接近。地面大风阶段对应着剧烈的闪电活动,地闪频数的跃增略提前于地面强风发生时间,这对灾害性天气过程的监测预警具有一定的参考价值。

One severe mesoscale convective system with damaging straight line wind occurred on 21 June 2005 in northern Shandong Province. Based on the analysis of lightning activities, radar echoes and cloud images, it was found that the cloud-to-ground （CG） flash rates increased rapidly at the initial developing stage, and they were very high （about above 20 fl per 5 minutes） all along the mature stage. At the dissipating stage, positive CG flashes gradually dominated. Almost all negative CG flashes occurred in the convective precipitation regions, whereas most positive CG flashes corresponded to stratiform precipitiation regions. The hourly flash rate lagged behind the minimum brightness temperature, and the area of cold cloud shield with temperature colder than --50℃ lagged behind the hourly flash rate. Strong wind at the surface occurred in or near the regions with dense CG flashes. The pulse of CG flash rate was slightly ahead of the occurrence of severe surface wind. The damaging straight-line wind was due to downbursts. The maximum wind speed observed at weather station was approximate to the maximum potential speed calculated by WINDEX.