Examining the influence of current waveform on the lightning electromagnetic field at the altitude of halo formation

Abstract

In this paper, we extend the analysis of Lu (2006) to calculate the electric field (E-field) of lightning return stroke in the region of sprite initiation and halos using a transmission line model that uses various lightning stroke current measured during the triggered lightning experiment as the driving source to examine the individual components (i.e., electrostatic, induction, and radiation) of E-field perturbation. As the altitude increases, the maximum strength of electrostatic and induction field gradually decreases, and the induction field decays slower than electrostatic field above 80 km. The electrostatic and induction field in the region of halo formation have a much larger contribution to the total E-field than the radiation field. Therefore, it is proposed that in addition to the electrostatic field, the induction field (with amplitude more than half of total E-field) is the main component of the total E-field within the first half millisecond directly above the stroke. Our analysis indicates that the induction field might play a significant role in the halo formation and probably also the sprite initiation. The M-component, the longer rising edge, the wavy long tail, and the relatively long time scale of stroke current can increase the amplitude of electrostatic and induction field at the height of halos, and drive the occurrence of halos and the subsequent development of streamers, therefore forming sprites. Our results enrich the understanding on the mechanism of halo production and the lightning electromagnetic field in the middle and high-altitude atmosphere, and also pave the way for future accurate modeling of halo formation.