Recent progress in lightning return stroke modeling and electromagnetic field computation

This review paper summarizes recent progress in lightning return stroke modeling and electromagnetic field computational methods. Recent work on electromagnetic and distributed-circuit models concerns essentially the inclusion of distributed nonlinearities along the channel. The nonlinear versions of electromagnetic and distributed-circuit models are able to reproduce experimentally-observed typical features of electromagnetic fields, especially the zero crossing of the remote fields. The equivalency between lumped-source and distributed-source models was the subject of recent investigations on engineering models, which have led to physical insight into the physics of lightning channel corona sheath. Other advances in engineering models concern a rigorous analysis of wave propagation along an extending transmission line which resulted in a revision of engineering models taking into account the reflections from the return stroke wavefront. The reflections are shown to be affected by relativistic Doppler effect. Recent studies on the identification of the main mechanisms responsible for the time of occurrence of the reversal of polarity in the far fields are described. Finally, the paper summarizes computational methods for the evaluation of electromagnetic fields along a lossy ground, with special emphasis on recent studies related to the case of inhomogeneous (vertically and horizontally stratified) ground.