Analyses On 3D Lightning Flash Activity Characteristics Of Three Different Types Of Severe Convective Weather Processes In Beijing

In this pater,based on the lightning data of VLF/LF 3D lightning location system from January 2015 to December 2016 in Beijing,the temporal and spatial characteristics of total lightning,intracloud lightning flashes(IC)and cloud-to-ground lightning flashes(CG)and the characteristic of the lightning current intensity were analyzed firstly.Then,combined with the data of radar,conventional observation data,and the data from intensive automatic weather stations,the characteristics of lightning activities and radar echoes in three different types of severe convective weather processes —— hailstorm,thunderstorm wind and torrential rain,were analyzed.The purpose is to reveal the mechanism of initiation and development of different types of severe convective weather further,to promote the operational ability to warn severe weather events such as hailstorm,thunderstorm wind,and torrential rain.The main conclusions are as follows.Most lightning flashes occur between June and September.The lightning flashes occur mostly from 15:00 BST of the day to 02:00 BST of the next day.There are two high value regions of spatial density of total flashes,and one is located in central and southern area of Mentougou and central and western area of Changping,the other is in the junction area among Miyun,Shunyi,and Pinggu.The high value regions of spatial density of IC and CG flashes have the distributions just as that of total flashes.The most IC occur at the height below 9 km and mainly concentrated in the height between 3 and 6 km.and when below about 15 km,the average intensity of lightning current is proportional to the height of IC.Otherwise,when above about 15 km,they are inversely proportional to each other.The lightning current intensity is mainly concentrated in the 5 ~ 50 kA,and the lightning current intensity greater than 100 kA rarely occur.The averaged lightning current intensity is smaller when the lightning frequency is higher,and the averaged lightning current intensity is larger when the lightning frequency is lower.The lightning flashes occur discretely in the echo region of 40 dBz when the meso-scale convective system(MCS)is a thunderstorm group.When the MCS intensifies and develops into a squall line with hook echo,the frequency of IC and CG increase and the lightning activity mainly concentrates in the leading edge of the squall line.In the hailstorm case,the proportion of IC flashes is increasing all the time,and the frequency of IC flashes exceeds that of CG flashes after the hail ends.In the thunderstorm wind case,the activity of IC is dominant throughout the convective process.However,in the case of torrential rain,the activity of CG,especially negative CG,is dominant.IC flashes occurs more often in the thunderstorms that produce hailstorms and strong wind.Among these three cases,the reflectivity intensity of thunderstorm causing torrential rain is relatively weak,but its frequency of lightning flashes is about 6 times higher than that of hailstorm and thunderstorm wind cases due to the large scope and long duration of convective cloud.In terms of the relationship between average lightning current intensity and the height of IC flashes,there exists a threshold in the height of IC flashes.And when the height of the IC flashes is not higher than the threshold,the average intensity of lightning current is proportional to the height of IC.Otherwise,when higher than the threshold,they are inversely proportional to each other.The relationship between the spatial and temporal distribution of lightning and that of precipitation is complex.The time of peak value of lightning frequency is often ahead of that of precipitation about 5-20 min,but there are also some exceptions such as a little lag or a simultaneous occurrence.