Modeling and Statistical Characterization of Preliminary Breakdown Pulses in Negative Cloud-to-Ground Lightning Flashes

Preliminary Breakdown Pulses (PBPs) are electromagnetic signatures of the process occurring in the early stages of a Cloud-to-Ground (CG) lightning flash, leading to the initiation of the downward stepped leader followed by the first Return Stroke (RS) retracing the leader channel. Their analysis can offer insights into the initiation of the lightning discharge process. Among the various lightning processes, PBPs remain less explored, although their study has the potential to improve lightning prediction and protection strategies. This study focuses on modeling PBPs using an engineering-model like approach (i.e, the Modified Transmission Line model by Karunarathne and coworkers, MTLK), exploiting its similarities with typical models for RS processes. The primary objective is to optimize the MTLK model parameters by fitting experimental electric field data from more than 3000 negative CG lightning flashes with peak current higher than 50 kA (as reported by the U.S. National Lightning Detection Network, NLDN). The fitting process, treated as an optimization problem, employs the Multivariate Ant Colony Algorithm for Continuous Optimization toolbox to minimize errors between predicted and observed electric fields. In this contribution, the statistical distributions of the parameters of the MTLK model are obtained, allowing the simulation of random lightning events in terms of PBPs and the corresponding RS. This could be useful for identifying the relationship between RS and PBP effects (e.g., on the induced voltage on power systems) and developing preventive tools for lightning protection based on PBP detection.