Using Saha-Boltzmann Plot to Diagnose Lightning Return Stroke Channel Temperature

Based on the high time-resolved spectra of a cloud-to-ground lightning flash with seven return strokes captured by a high-speed slitless spectrograph, this work was the first to use the Saha-Boltzmann plot method for the determination of the lightning return stroke channel temperature. The channel temperatures of the seven return strokes ranged from 21370 to 26500 K. Compared with the traditional Boltzmann plot method, the Saha-Boltzmann plot method can provide more reliable temperature estimation for lightning channel. Analysis of several strong return strokes along the channel showed that the temperature changed little and there was no obvious tendency with increasing height. In addition, it was found that the channel temperature in the late stage of a return stroke was only about 3000-4000 K lower than in the initial stage. This means the channel remains > 20000 K during nearly the entire period of the return stroke. This sustained high temperature could be the main cause of lightning-related disasters.