典型强龙卷风暴中的地闪活动特征

CHARACTERISTICS OF CLOUD-TO-GROUND LIGHTNING ACTIVITIES IN TYPICAL SEVERE TORNADO STORMS

关键词:  强龙卷  地闪  正地闪  雷电流

Key words:  severe tornado  cloud-to-ground lightning  positive cloud-to-ground lightning  lightning current

摘要:

闪电活动对于强龙卷天气的发生有一定的指示作用，基于闪电定位资料，结合多普勒天气雷达、探空和ECMWF再分析资料对两次典型强龙卷风暴中地闪的时空演变、雷电流强度及正地闪活动特征进行了统计分析，结果表明：地闪主要发生在组合反射率因子≥30 dBZ的区域内，龙卷发生期间，地闪活动减弱且较为分散。不同龙卷风暴的地闪频次差异较大，这与风暴中上升气流的强度有关；当地闪频次从峰值降至最小值期间，龙卷及地，两次过程中地闪频次峰值分别提前龙卷发生约33 min和28 min。同时，龙卷及地之前，地闪会出现连续多次闪电跃增；龙卷等级越强，正地闪表现越活跃，特征越明显，在江苏盐城阜宁龙卷发生期间，还出现了地闪极性从正地闪主导向负地闪主导的反转；两次龙卷风暴雷电流强度随时间的变化规律并不明显，但均小于历史平均值，地闪发生愈频繁的龙卷风暴，对应的雷电流强度值愈小。

Abstract:

Lightning activity could be an indicator of the occurrence of a tornado. Based on lightning location data, Doppler radar data, sounding data and ECMWF reanalysis data, the spatio-temporal evolution of cloud-to-ground (CG) lightning, the intensity of lightning current and the features of positive CG lightning in two typical severe tornado storms are analyzed. The results show that CG lightning mainly occurs in the area with composite reflectivity greater than 30 dBZ. When tornadoes occur, CG lightning activities decrease and are relatively dispersed. Due to the different intensities of updrafts, CG lightning frequencies vary greatly in different tornado storms. Tornadoes touch down during the period when CG lightning frequency decreases from the maximum to the minimum. In the two cases, the maximum frequency of CG lightning appears 33 minutes and 28 minutes ahead of the tornado occurrence. Before tornadoes touch down, there are several lightning jumps. Moreover, the higher the tornado event level, the more positive CG lightning occurs, and the more obvious the positive CG lightning characteristics are. A CG lightning polarity reversal from positive-dominated to negative-dominated happens during the tornado episode in Funing County, Yancheng City. Within the lifecycles of the two tornadoes, the lightning current intensity does not vary significantly and is smaller than the historical mean. It is found that the more frequently CG lightning occurs in tornado storms, the smaller the lightning current intensity will be.