On the mechanisms that lead to current cutoff and multiple ground contacts in lightning

Abstract

This research project aims at the analyses of two main questions: (i) How does the process of channel current cutoff occur in lightning (particularly in the context of the bidirectional leader model)? (ii) What is the nature of the lightning flashes that create multiple ground contact points? The first analysis will be based primarily on data from a network of slow electric field antennae and VHF time-of-arrival sensors for three-dimensional mapping of lightning channels known as LMA (Lightning Mapping Array) that were installed in a wind farm. A small number of events will be selected for detailed case studies, which will also be used to evaluate the different models for channel current cutoff found in literature. The second analysis will be conducted from data provided by VLF/LF large scale lightning locating systems (LLS) for a much larger number of events. From this database the effect of topography and terrain features over the occurrence of lightning flashes that create multiple ground contacts will be evaluated. For the first analysis we propose to conduct the case studies and the modelling of channel charge distributions during the period in which the scholarship candidate will be allocated at the University of Arizona. For the second analysis it was planned that the discussions and eventual re-analyses will be initiated during the candidate stay in Tucson, Arizona. This will allow vital inputs from Dr. Cummins during the constant personal meetings and discussions, taking advantage his supervision and vast experience in the analysis and modeling of electromagnetic signals emitted by lightning. (AU)