Propagation characteristics of ion acoustic waves in lightning plasma channels

The propagation characteristics of ion acoustic waves (IAWs) in lightning plasma channel were investigated by combining theoretical modeling with spectroscopic diagnostics. Considering warm N II ions and hot-isothermal Boltzmann electrons, the Korteweg de-Vries (KdV) equation was derived using the reductive perturbation technique. The calculation results show that the ion-to-electron temperature ratio plays a crucial role in determining the characteristic parameters of IAWs, such as phase velocity, amplitude, and width. As the plasma evolves from a non-Local Thermodynamic Equilibrium (NLTE) state toward a near-Local Thermodynamic Equilibrium (LTE) state, the IAWs exhibit larger phase velocities, lower amplitudes, and narrower spatial widths. In realistic lightning plasma channel, by performing dimensional analysis, it is found that the phase velocity of IAWs is more sensitive to the variation of ion temperature than amplitude and width. Thus, the phase velocity can be regarded as an important indicator for investigating the transition of lightning plasma from NLTE to LTE states. In the LTE state, the phase velocity and amplitude are positively correlated with electron temperature, while the width depends on both electron temperature and electron density. This work exhibits potential application value in investigating the electron–ion coupling mechanisms and energy transfer characteristics in lightning plasma.