We propose a new method of estimation for the amount of charge removed by individual lightning flashes in thunderclouds by means of three-dimensional (3D) VHF images and the associated electric field (E-field) change on the ground. In this method, we assume a reasonable assumption that the VHF sources located by the VHF broadband digital interferometers (VHF DITFs) correspond to charge transfer of each breakdown. We examine 3D VHF images recorded in Darwin, Australia and estimate the amount of charge removed by lightning discharges in thunderclouds. The average amount of charge removed in a CG and an IC flash is 28 C and 33 C, respectively. These results are in reasonable agreement with previous estimations for the amount of charge transferred using E-field measurements. The charge density removed by an IC flash was also estimated to be 4.3 × 10-10 C/m3 for the positive charge region and 5.8 × 10-9 C/m3 for the negative charge region, respectively. The estimation results indicate the charge structure before the flash occurred in thunderclouds.
The impact is evaluated of nearby trees and bushes on the effective height of a vertical electric antenna in the extremely low frequency (ELF) band. We try to find the distance at which the plants might influence the local quasi-static field and thus disturb the effective height of antenna. The obtained results might be helpful when choosing the place of antenna positioning in the long-term ELF monitoring.