Two-Dimensional Striking Distance of Lightning Flashes to a Cluster of Tall Buildings in Guangzhou

摘要

Based on the high-speed video records of 54 lightning flashes striking on a cluster of tall buildings in Guangzhou and the return stroke peak currents provided by lightning location systems, this paper analyzed the two-dimensional (2D) first-return-stroke striking distances (SD) of lightning flashes to buildings with a height ranging from 100 to 600 m. Three methods, including one proposed in this study, have been used to estimate the 2D SD. The results with different methods basically agree with each other and show that the height and the top geometry of the structure on which lightning terminates are key factors that affect the SD. The correlation between the SD and the peak return stroke current appeared very scattered, particularly in the cases when each building was considered separately. Besides, we found that: (a) the estimated 2D average initiation speed of upward connecting leader (UCL) on different buildings are similar, ranging from 4.9 to 23 x 10(4) m/s, with an average of 13.4 x 10(4) m/s; (b) about 87% (27/31) flashes that struck on buildings with simple top shape only have one upward leader observed, while for buildings with complicated top shape, only 26% (6/23) flash cases have one upward leader observed; (c) for the 36 flashes to four tall buildings with heights higher than 300 m, the 2D average speed ratio of the downward leader and the UCL is 0.74 during the last 0.1 ms before the first return stroke.