The Evolution Of Current And Channel Radius In Cloud-to-ground Lightning Return Stroke Process

Research on lightning discharge physical process is the theory basis for lightning warning and protection work.Observation of lightning spectrum is an effective way to obtain the internal physical parameters of the lightning channel.This thesis mainly analyzes the high time-resolved spectrum of cloud-to-ground lightning captured by the recording equipment of high-speed slitless spectrograph in Qinghai Plateau.Many physical characteristics,especially,electric current evolved with time of return stroke process in cloud-to-ground lightning have been discussed through the time evolution of spectrum.The main contents and results are as following:According to the spectra of cloud-to-ground lightning discharge processes and the synchronous electrical observation data,combined with the theoretical calculation,the physical characteristics of two lightning with multiple return strokes are analyzed.A positive correlation between discharge current and intensity of ionic lines in the spectra is verified,and based on this characteristic,the current evolution characteristics during four return strokes are investigated.The results show that the current drops to the half-peak value in about 101?s-139?s.The Joule heat in per unit length of four return strokes channel is in the order of 10~5J/m-10~6J/m.The radius of arc discharge channel is positively related to the discharge current,and the more intense the current is,the greater the radius of channel is.Furthermore,the evolution for radius of arc core channel in the process of return stroke is consistent with the change trend of discharge current after the peak value.All physical characteristic parameters calculated agree well with the results reported in other literature,which demonstrates the data from this work is reliable.In addition,for the lightning with no electrical observation data,there is not direct method for estimating the peak current of discharge channel.With the electric field change of other lightning as reference,combining the Beer-Lambert law,the intensity of spectral lines of different lightnings is unified to the same observation distance.Based on the positive correlation between discharge current and intensity of ionic lines in the spectra,the evolution characteristics of current for another lightning are further investigated.The results show that the current dropping from the peak to the half-peak value needs 101?s-138?s,and then decays slowly.The physical parameters of lightning discharge channel are calculated in a reasonable range.Due to the relatively easy implementation of spectral observations,it provides a new way to study the lightning discharge current and the transmission characteristics.