Review of recent developments in lightning channel corona sheath research

A review of recent lightning channel corona sheath dynamics research is given. Current state of knowledge about corona sheath conductivity is presented and a brief discussion on the role of radially flowing corona current in longitudinal extension of the channel is given. It is shown that positive transferred charge inside the lightning channel core during the return-stroke stage dominates the total charge when the speed of the return stroke current wave is relatively low and the negative leader line charge density is less than typical values inferred from field measurements. As a result, the positive charge inside the channel during the return-stroke stage can be temporarily greater than the negative charge deposited by the preceding leader. This may explain significant positive overshoots in radial electric fields measured close to the lightning attachment point at ground. Consequences of adoption of corona current concept in the Lumped Current Source (LCS) type models are described, and duality between LCS type models and the Distributed Current Sources (DCS) type models is rigorously demonstrated. Additionally, we discuss the role of corona in making the return-stroke speed lower than the speed of light.