The Current Variation Along The Discharge Channel In Cloud-to-ground Lightning

Lightning return stroke current is always a significant parameter in lightning protection.The uncertainty of lightning occurrence makes it very difficult to measure the return stroke current directly,and the change of current along the channel cannot also be obtained directly.The importance of the change of current along the channel is mainly reflected in the study of the physical mechanism of the energy transmission and discharge process accompanied by the occurrence of lightning.However,the investigation about the current change along the channel are all based on theoretical models,and It is not yet possible to study the change of current along the channel based on experimental observations.In this work,Thirty-six spectral observation data of nine cloud-to-ground lightning return strokes channels in qinghai plateau region are obtained by a slit-less high-speed spectrograph.Combining synchrotron radiation electric field data,according to the positive correlation between discharge current and the ionic lines intensities of the spectra,change characteristics of return stroke current along the discharge channel are investigated.The result shows that there are three types of the variation trend for discharge current with the increase of height along the channel,they are exponential attenuation,linear attenuation and basically unchanged,respectively,these three change trends are the same as the changes of current with the channel height in the theoretical model which are MTLL,MTLE,MULS,DU model and TL,BG and TCS models of return discharge.The attenuation coefficient(the attenuation index and the slope)is roughly positive correlated with the discharge intensity.In the process of strong discharge,discharge current tends to decreaseexponentially along the return stroke channel.In addition,in the same return stroke of the same lightning,the initial return stroke current decays the fastest.In different return strokes of the same lightning,the current attenuation gradually flattens with time.