Evolution Of Positive Cloud-to-ground Lightning Discharge Characteristics Along The Channel

Positive lightning is a comparatively rare discharge activity,accounting for less than 10% of global cloud-to-ground lightning.positive lightning is of particular interest because it is responsible for the largest of the recorded lightning currents,those in the 200-300-KA range,and attracted wide publicity than those of negative flashes.The current transmission characteristic of positive lightning is the core problem of lightning protection design.Because the occurrence of lightning is instantaneous and random,at present,there is no experimental method to directly observe the change of lightning current along the channel and the related research is based on the theoretical models.Some physical parameters,such as temperature,conductivity,can be reflected by using the data of lightning spectrum.Conductivity is an important parameter to reflect the current carrying capability of discharge channel,and the spectral line intensity of different excitation energy is closely related to discharge current.Therefore,investigation on the variation of discharge current based on high time-resolved spectrum of lightning full channel is of great significance to further analyze the transmission characteristics and microscopic mechanism of the discharge current.In this work,combined with spectrum and synchronous electric field change information,the intensity of ionic lines as well as the variation of plasma channel electron density and conductivity along the channel in the spectrum of the downward positive lightning discharge process were investigated.Based on the positive correlation between the total intensity of ion lines in the spectrum and the current,the variation of positive CG lightning current along the channel is analyzed.The results show that the total intensity of the ion lines,electron density and conductivity increase with the increase of channel height.Compared with the attenuation characteristics of downward negative CG lightning current studied before,it is found that the change of current along the channel has common characteristics during the downward discharge of positive and negative lightning,that is,the trend of attenuation along the current direction.It is inferred that the change of current on the discharge channel is related to the direction of lightning current transmission.This work provides a reference for further study of lightning current transmission mechanism.