Lightning Initiation as a Consequence of Natural Thundercloud Evolution. Part 2. Pre-Streamer Stage

Abstract

The article presents the second part of the authors’ lightning initiation scenario, which is a continuation of the study [1]. In the first part it was shown that, if the detachment of electrons from negative ions is taken into account, the air breakdown field reduces by 15–30 %. This partially simplifies but does not solve the problem of lightning initiation in a thundercloud, the maximum electric fields in which are approximately an order of magnitude lower than the dielectric strength of air. This article addresses the lightning discharge inception scenario pre-streamer stage. It describes how a series of corona discharges that occur during collisions (nearly collisions) of hydrometeors seeds the cloud with decimeter-scale regions having increased ionic conductivity. The electric field at the poles of these regions enhances to a level necessary for positive streamers to appear. It is shown that, for a transition from millimeter-scale corona discharges to decimeter- or meter-scale streamers to occur, a spatiotemporal frequency of corona discharges on hydrometeors higher than 0,1 m-3s-1 is required, which may well be achieved in a typical thundercloud. The final stage, at which streamers oriented by the direction of a large-scale electric field are combined into a single plasma network, within which a hot leader channel forms, will be described in the coming part of the study.