Key Laboratory of Middle Atmosphere and Global Environment Observation (LAGEO), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China.
Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of information Science & Technology, Nanjing, 210044, China.
Sci Rep. 2017 Jun 14;7(1):3457. doi: 10.1038/s41598-017-03686-w.
A fundamental question in lightning flash concerns why the discharge channel propagates in a zig-zag manner and produces extensive branches. Here we report the optical observation of two negative cloud-to-ground lightning discharges with very high temporal resolution of 180,000 frames per second, which shows in detail the dependence of channel branching and tortuous behavior on the stepping process of the leader development. It is found that the clustered space leaders formed in parallel ahead of the channel tip during an individual step process. The leader branching is due to the multiple connection of the clustered space leaders with the same root channel tip, which occur almost simultaneously, or successively as some space leaders/stems resurrect after interruption. Meanwhile, the irregularity of angles between the clustered space leaders and the advancing direction of leader tip is the origin of channel tortuosity. The statistical analysis on 96 steps shows a geometric-mean value of 4.4 m for the step length, ranging between 1.3 and 8.6 m, while the distance from the center of space leader to the channel is 3.6 m, ranging between 2.1 and 6.9 m. More than 50% steps occurred within an angle range of ±30° from the advancing direction of the leader.
闪电放电中一个基本问题是为什么放电通道呈之字形传播并产生广泛的分支。在这里，我们报告了两次负地闪放电的高速光学观测结果，时间分辨率高达 180,000 帧/秒，详细显示了通道分支和曲折行为与先导发展的步进过程的依赖关系。研究发现，在单个步进过程中，簇状空间先导在通道尖端前方平行形成。先导分支是由于簇状空间先导与同一根通道尖端的多次连接所致，这些连接几乎同时发生，或者当一些空间先导/茎在中断后复活时会相继发生。同时，簇状空间先导与先导尖端前进方向之间的角度不规则性是通道曲折的起源。对 96 个步长的统计分析表明，步长的几何平均值为 4.4 m，范围在 1.3 到 8.6 m 之间，而空间先导中心到通道的距离为 3.6 m，范围在 2.1 到 6.9 m 之间。超过 50%的步长发生在先导前进方向的±30°角度范围内。
