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

Abstract

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 CG 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.

Numerical simulation of the effect of lower positive charge region in thunderstorms on different types of lightning

“…Akita et al [2011] found that the negative leaders of negative CG flashes propagated a horizontal distance about 10 km in cloud first, and then bent to reach ground, but they did not give an explanation.…”

“…The propagation behavior of lightning channels and the reason for formation of different types of lightning have been difficult problems in lightning scientific research field for a long time. With the development of modern observation and numerical simulation techniques, numerous studies indicated that lightning types, polarity, and propagation behavior may be closely related to the charge distribution of thunderstorms [e.g., Mazur and Ruhnke 1998;Zhang et al 2006;Krehbiel et al 2008;Zheng et al 2010;Akita et al 2011]. The typical charge distribution of thunderstorms is dipole or tripole charge structure, and the difference between them is whether there is an LPC region [Williams 1989].…”

Initial results of LF sensor network for lightning observation and characteristics of lightning emission in LF band

“…VHF DITF is a 2D VHF lightning mapper [Yoshida et al, 2012a] that enables obtaining 3D lightning images when two or more VHF DITFs simultaneously locate one flash [Morimoto et al, 2004;Akita et al, 2010;Yoshida et al, 2010;Akita et al, 2011]. VHF DITFs were operated at Sites 1 and 5 ( Figure 1).…”

Lightning Observation in 3D Using a Multiple LF Sensor Network and Comparison with Radar Reflectivity

“…5, 6, and 9 were negative [13]. Akita and colleagues [26] observed lightning discharges in Darwin, Australia, and reported that IC discharges developed in the upper positive charge regions in thunderstorms. In this study, it seems that positive charges existed in the regions where negative leaders of IC discharges developed.…”

“…9. In a thunderstorm, ice pellets are charged positively by the noninductive charging mechanism [26]. In the precipitation radar observations, the radar reflectivity of ice pellet regions is lower than that in graupel or hail regions [27], and thus it is likely that positively charged ice-pellet regions existed in the region where the negative leaders developed.…”