Spectroscopic method to study the effect of lightning return stroke channel expansion on atmospheric pressure

Abstract

Using the plasma radiation spectra of three natural cloud-to-ground multi-strike lightning discharges recorded by a slitless grating spectrograph, and based on the spectral wavelengths and relative intensities, combined with information about the lightning-synchronized ground electric field variations, we calculated the temperatures, line-charge densities, initial radii, and final radii of the lightning-strike channels. This was achieved by applying the theory of air plasma transport, lightning electrodynamics, the laws of conservation of energy and pressure. Subsequently, we determined the initial internal energies of the lightning plasma channels, the final internal energies, the work done by the return stroke channel expansion against atmospheric pressure, equivalent impedances, and the speed of charge movement. The results show that the temperature of the return stroke channel and the work done by the expansion of the return channel on the atmospheric pressure decrease with the development of the return stroke process. The final radius and the initial internal energy, as well as the initial peak electric field and the work done by the return stroke channel expansion on the atmospheric pressure, exhibit a strong linear relationship. The equivalent impedance and speed of charge movement show a nonlinear relationship with the work done by the return stroke channel expansion against atmospheric pressure. The changes in initial internal energy, final internal energy, and the expansion work of the return stroke channel against atmospheric pressure are essentially consistent and positively correlated. The initial peak electric field of the return channel increases, leading to enhanced spectral intensity. The return stroke channel temperature, initial radius, final radius, initial internal energy, final internal energy, and the work done by the return stroke channel expansion against atmospheric pressure all increase. Meanwhile, the equivalent impedance and speed of charge movement decrease.