Analysis Of Characteristics Of Artificially Induced Lightning Connection Process

The attachment process of lightning is one of the weakest links in the current research of lightning physics,and it has been closely followed by the academic community for a long time.Based on SHAndong Triggering Lightning Experiment(SHATLE),We investigate the physical mechanism of the lightning attachment process from the perspective of experimental observation and supplemented by space electrostatic field simulation.This study is aimed at providing an important reference for the design of the lightning protection technology and the selection of parameters in the application of lightning protection technology.We investigate two special rocket-triggered lightning with simultaneous high-time resolution data.The main findings are as follows:1.The altitude rocket-and-wire technique was used to trigger lightning to strike a30-m-high communication tower.A comprehensive dataset was obtained,including discharge current and electromagnetic-fifield changes,as well as high-speed video images.An attachment process with an abnormal circuitous S-shaped connection channel was observed between the lower extremity of the triggering wire and the tower top,with a total channel length of 25.3 m,which was much longer than the direct connection channel of 13.0 m.The downward negative leader from the triggering wire and the upward connecting positive leader from the tower top“missed”each other by a vertical distance of 4.1 m before turning to the horizontal direction and eventually completing the breakthrough phase.The attachment process produced a sharp current pulse with a duration of 19?s and a peak of 11.6 k A,transiently promoting the upward positive leader development from the upper extremity of the triggering wire.The simulation of the background electric fifield indicated that the electric fifield surrounding the tips of the initial leaders did not involve a dominant direction with pronounced larger intensity.The leader streamer/corona zones with a divergent feature resulted in directional uncertainty for the initial steps.As the leaders developed and the associated streamer/corona zones expanded,the attraction effffect was enhanced and the leaders turned to the horizontal direction.The common streamer zone(CSZ)developed when the gap between the leaders was about 8 to 9 m,resulting in the occurrence of the breakthrough phase and accomplishment of the attachment.For the last return stroke,the long interstroke interval facilitated channel cooling and a decrease in conductivity.This promoted the occurrence of a dart-stepped leader instead of dart leader,and led to the alteration of the attachment route from an S-shaped channel to a direct connection channel.2.By conducting close observation on a rocket-triggered lightning,we quantitatively investigated the attachment process when the lightning is triggered and the attachment process of the subsequent strokes with simultaneous data of optical current and electromagnetic field changes at fine time resolution.The bottom of the wire was only 1.6 m away from the tip of the drainage rod when the lightning was triggered.The time interval between the initial of the upward connection leader from the tip of the drainage rod and downward negative leader the end of the triggering wire was 53.8?s.Before the establishment of the CSZ,the downward negative leader has been developing downwards at a uniform speed(a variable speed during the period),while the upward connection leader has not been significantly developed in the vertical direction.The length of the BTP was about 0.15 m,and the duration ranged from 7.7to 15.4?s,and the propagation speeds of the positive and negative leader in the CSZ were 10~4m/s.The time interval between two subsequent strokes was 63 ms.In the frames prior to the two subsequent strokes,the lengths of the upward connection leaders were 3.6 m and 2.7 m,and the heights of the connection point were estimated to be 4.3 m and 5.2 m,respectively.The electric field waveform of two subsequent strokes at 6 km exhibited classical slow front and fast transition.The durations of the slow front and fast transition of two subsequent strokes both were 0.5?s and 0.65?s,respectively.No LBs(leader brusts)could be observed from the electric field waveforms of the two subsequent return strokes.