Effects of Charge Distribution in Thunderstorms on Lightning Propagation Paths in Darwin, Australia

The charge distributions in a thundercloud play an important role in the initiation and propagation of lightning discharges. To further understand the effects of charge distributions on lightning discharge, the authors conducted a very high-frequency (VHF) lightning observation campaign during the 2006/07 monsoon in Darwin, Australia, using a VHF broadband digital interferometer (DITF). A C-band polarimetric weather radar to estimate the precipitation profiles such as hydrometeor classification was operated by the Bureau of Meteorology (BOM) Research Centre. Cloud-to-ground (CG) and intracloud (IC) flashes were initiated from the outer and the inner parts of the upper side of the graupel regions, respectively. In the cases of CO flashes, the negative leaders travel first about 10 km horizontally through positive charge regions and then begin to bend toward the ground when they reach the edge of the positive charge regions where there is no graupel region underneath. In contrast, in the cases of the IC flashes the negatively charged graupel regions block the downward developments of negative leaders. It is noted that positive charge regions could facilitate the extension of the horizontal negative leader. These results may suggest that lightning flash types are closely dependent on their initiation locations and the surrounding charge distributions. The experimental results are consistent with other previous observation results and charge model simulations.