北京一次大雹天气过程的闪电活动特征分析

由于受闪电监测系统限制,已有研究多局限于强对流天气的地闪(cloud-to-ground lightning,CG)活动特征。本文利用VLF/LF三维闪电监测定位资料,结合雷达观测等资料对北京地区一次典型大雹天气过程的全闪活动特征进行了分析。结果表明:降雹发生前,闪电活动主要分布在对流系统的后部,闪电数较少,且以负地闪活动为主;降雹期间,闪电频数显著增加,云闪(intracloud lightning,IC)及正地闪活动明显加强,该阶段闪电活动主要集中在对流系统强回波中心及其前部雷达反射率因子梯度较大的区域;降雹结束之后,强回波中心基本移出北京,北京范围内的闪电频数明显减少。正闪比例在降雹发生前逐渐增大,在降雹期间稳定维持在较大值,降雹结束后迅速减小;云闪比(云闪频数/总闪频数)表现为降雹发生前和降雹结束后逐渐增大趋势,在降雹期间基本维持稳定少变。闪电的电流强度主要集中在5—50 kA之间,20 kA以下的低雷电流强度的云闪和地闪多发生在降雹期间及降雹结束后,而20 kA以上的高雷电流强度的云闪和地闪在降雹发生前占有很大比例,小于5 kA的云闪在大雹发生期间所占比例明显高于地闪。降雹发生前及降雹结束后云闪发生高度在2-6 km,降雹期间有所抬升,约为2-8km。闪电频数峰值超前于降水峰值5-20 min。

Analysis of lightning flash activity characteristics of a severe hailstorm process in Beijing

Due to the limitations of the lightning monitoring system,the existing studies were mostly limited to the cloud-to-ground lightning (CG) activity characteristics in the severe convective weather.In this paper,the data from the VLF/LF three-dimensional lightning monitoring and positioning system and radar observation stations were used to analyze the full lightning activity characteristics during a typical large hail weather process in Beijing.The results show that before the hail,the lightning activity is mainly distributed in the rear of the convection system,and the number of lightning is small,and the negative lightning activity is dominant.During the hail period,the frequency of lightning flashes (FLF) increases significantly,and the intracloud lightning (IC) and positive CG activities are significantly enhanced.The lightning activities in this stage are mainly concentrated at the center of the strong echo area and the regions with a large gradient of the front radar reflectivity factor of the convection system.After the hail,the strong echo center moves out of Beijing,and the FLF in Beijing decreases significantly.The proportion of positive lightning increases gradually before the occurrence of hail remains stable at a large value during the period of hail,and decreases rapidly after the end of hail.The IC lightning ratio (the frequency of IC lightning/the frequency of total lightning) shows a gradually increasing trend before and after the hail,and basically remains stable and changes little during the hail.The lightning current strength is mainly concentrated in the 5-50 kA.The IC and CG with current intensity below 20 kA mostly occur during and after the hail,and those above 20 kA are dominant before the hail.The proportion of IC with a current intensity of less than 5 kA is higher than that of CG during the hail.Before and after the hail,the IC occurs at an altitude of 2-6 km,and increases during the hail,to about 2-8 km.The peak of FLF is 5-20 min ahead of that of precipitation.