Three-dimensional lightning observations of cloud-to-ground flashes using broadband interferometers

For the first time, the broadband radio interferometers have been developed to locate the sources of VHF/UHF radiation from lightning discharges in three spatial dimensions (3D) and time. The lightning observations have been conducted in Darwin, Australia during summer 1998 at two different sites. Each site consisted of a broadband interferometer and an electric field sensor as well as a GPS receiver. The triangulation scheme was proposed to estimate the 3D source locations. The system was able to observe different types of lightning discharges and estimate the initial and subsequent leader progression speeds from three negative cloud-to-ground lightning flashes. The initial leaders had progression speeds of about 10(5) m s(-1), typical for negatively charged initial leaders. The preliminary activity prior to the initial leader progression was also recognized. In cloud K-processes, a dart leader and an attempted leader were also found to be negative-polarity discharges and they propagated either upward or downward to ground with the estimated speeds of about 10(6) m s(-1), in agreement with previous studies. Two of the flashes contained subsequent leaders that took different channels and created new terminations on ground. These subsequent leaders required long duration to progress downward (about 35 and 65 ms) with the same speed as typical initial leaders before reaching the ground. (C) 2002 Elsevier Science Ltd. All rights reserved.