Lightning Activity Of Hailstorms In Beijing-Tianjin Region

The characteristics of lightning activity of sixteen hailstorms from 2005 to 2009 in Beijing and Tianjin and the relationship between lightning activity and hailstorm structure are investigated mainly based on the total lightning data observed by SAFIR3000 system, cloud-to-ground (CG) lightning data by a CG lightning location system (LLS) and echo data of Doppler radar. Besides, the dynamic and microphysics mechanism in hailstorms are analyzed by comparing two hailstorm processes.Hailstorms generally featured much lower proportion of cloud-to-ground lightning, with the average value of 4.43% in sixteen hailstorms. However, the average proportion of positive cloud-to-ground (PCG) lightning was 50.48%, which is much higher than that in typical thunderstorms. Additionally, there was a positive correlation between the proportion of PCG and the diameter of hail. The higher the proportion of PCG was, the larger the diameter of hail tended to be. The results show that the region of strong lightning activity and the central hail-falling region were not overlapped, it located to the front of the hail-falling region, and more trended to occur in the right of. In seven of sixteen events, total lightning frequency increased sharply over a short period before the occurrence of hailstones, and the average lead-time was 26.04min. Besides, the lightning activity had a better correlation with the volume of radar echo, especially with the volume of echo larger than 40dBZ. The result of power fit of the total lightning frequency as a function of echo volume was better than linear fit. Two hailstorms were investigated. The second active stage of lightning discharge exhibited two different mechanisms:firstly, the enhancement of the convection after the hailfall was responsible for the strengthened charging process and led to the active lightning discharge in the second stage. Secondly, the weak hailfall urged the ice particles to aggregate at middle-low levels, and then formed a strong region with a mass of charge here, which resulted in the lightning activity strengthened again during the period when the thunderstorm continuously weakened after the hailfall.