Lightning observations and consideration of positive charge distribution inside thunderclouds using VHF broadband digital interferometry

The Lightning Research Group of Osaka University (LRG-OU) has been developing a new type of lightning location and monitoring system based on a technique of “VHF broadband digital interferometry”. Lightning observations have been conducted in Darwin, Australia during summer and in Fukui, Japan during winter thunderstorm seasons. In these observations, imaging of lightning progression is realized in four-dimensions that means space and time. Since VHF impulses are radiated from mainly negative breakdowns, their source location gives the positive charge distribution. In other words, the broadband interferometer may not only visualize negative leader progressions but also give information on positive charge distribution inside thunderclouds. Consulting radar observations confirms this interpretation.