Unusual Plasma Formations Produced by Positive Streamers Entering the Cloud of Negatively Charged Water Droplets

Abstract

AbstractKostinskiy et al. (2015b), https://doi.org/10.1002/2015GL065620, using a high‐speed infrared (2.5–5.5 μm) camera, discovered the so‐called unusual plasma formations (UPFs) in artificial clouds of charged water droplets. UPFs had complex morphology including both streamer‐like regions and hot channel segments. They were observed both in the presence and in the absence of hot leader channels developing from the grounded plane toward the cloud. In this paper, which is aimed at revealing the genesis of UPFs, we present two UPFs that occurred inside the initial corona streamer burst of positive polarity emitted from the grounded plane, prior to the formation (or in the absence) of associated hot leader channel. These streamer bursts developed at speeds of 5–7 × 105 m/s over 1–1.5 m before entering the optically visible negatively charged cloud and producing UPFs at its periphery. Hot channel segments within UPFs were formed in very short times of the order of 1 μs or less. It is not clear if the UPFs were caused solely by the enhanced electric field near the charged cloud boundary or other factors also played a role. Occurrence of UPFs may be a necessary component of the lightning initiation process.