Analysis Of Lightning Characteristics Based On SAFIR Data In Beijing And Its Circumjacent Regions

Lightning is a severe discharge in atmosphere and its damage is paid more and more attention. The analysis of lightning location data can help us understand the characteristics of lightning flash and provide reliable base for lightning protection.The analysis of lightning location data, mastering law of lightning activity and increasing knowledge of lightning could provide a reliable basis for lightning protection. In this paper, the principle of work and system components of SAFIR3000 are introduced. After then, the lightning data observed by SAFIR3000 lightning location system from Jan 2005 to Dec 2007 in Beijing and its circumjacent regions (Tianjin,Tangshan, Langfang, etc.) are chosen and the quality control of the data is taken.Then the temporal and spatial characteristics of intracloud (IC) flash and cloud-to-ground (CG) flash and some related lightning parameters are analyzed through mathematical statistics, normalization, comparison methods. In addition, the lightning location data in 2008 between SAFIR3000 and ADTD system are compared. The results obtained in this study are as follows:The time of high IC frequent by observed by SAFIR3000 mainly focuses from 15:00 to 24:00 and the peak of the IC frequency is at 19:00. Most of IC flashes are prone to occur between June and August, and the peak occurs in July. The maximum of spatial density of IC mainly clusters in the east and central of Beijing, in the north of Tianjin and southwest of Chengde with the value of 30 fl/km2·a. The average height(MSL) of IC lightning initiated is about 10.9km and its diurnal variation has few difference. The initiated height is highest in summer, whereas lowest in winter. The IC flashes mainly occur the height of 9～10km, which account for 10.97% of the total IC flashes, and there are small differences in height distribution in various regions. The high frequency time, months, the high density area (about 5 fl/km2·a) of CG lightning are similar to IC lightning. However, a few differences appear between IC lightning and CG lightning. Firstly, the daily variation of IC has a single peak but the CG's has two peaks; Secondly, the beginning and end time of high value of the former are earlier than the latter's. In addition, the lightning density of the former is 6 times larger than the latter's. The average current of +CG is 32.62kA, while -CG is -30.35kA. The monthly variation of current of +CG is obvious, but -CG is not. The average percentage of +CG flashes accounting for total CG for three years is 16.44% and the percentage is lower in summer but higher in spring and autumn.The average rise time and decay time of current waveform observed by SAFIR3000 are 6.07μs and 26.61μs, respectively. It's also found that the temporal variation has a inverse correlation between rise time and fall time. The mean stroke of per lightning is 1.57, of which +CG flash is 1.19 and -CG flash is 1.64. The single-stroke flashes of+CG lightning account for 87.24% and -CG lightning for 65.22%. The mean time interval between strokes is 65.03ms and duration time of CG flash is about 0.03ms-948.4ms. Normalized to 100km, the radiation field of first return stroke of positive flash is 5.28V/m while negative flash is 6.09V/m. The average propagation speed of the IC lightning channel is about 1.81×104km/s.Through comparing the lightning data in 2008 between SAFIR3000 and ADTD system, it is found that the lightning frequency and current observed by SAFIR3000 are lower than ADTD's. However, the variation characteristics of lightning frequency and current between the two systems are similar.