Exploring the relationship between lightning discharge current and plasma spectrum

Lightning return stroke discharge current is a key parameter being concerned in lightning protection design. Since the current of natural lightning is difficult to be directly measured, and the existing experimental methods cannot obtain the information of the current change along the channel, the correlation between the current intensity and the corresponding spectral characteristics makes it possible to investigate the current transmission characteristic. The high time resolution spectra of the whole channel outside the cloud for nine multi-return cloud-to-ground (CG) lightning discharges were captured by using a high time-resolved slit-less spectrograph, and the light radiation characteristics of the discharge plasma channel have been investigated. Based on plasma spectral diagnosis method, combined with the synchronous electric field change waveform caused by lightning, using the relationship between electric field variation amplitude and the corresponding discharge current, the dependence of spectral characteristics on discharge current intensity was analyzed. We found that the intensity of the ionic lines in the spectrum are positively correlated with the current intensity. Semi-empirical data fitting shown that for most of the lightning studied in this work, there is a good quadratic correlation between ionic lines intensity and peak current. The correlation between spectral characteristics and discharge current intensity depends on the radiation mechanism of spectral lines with different excitation energy. The intensity of the ionic lines in the spectrum can reflect the current intensity in more detail than the total luminous intensity.