Journal of Atmospheric Electricity

This study investigates the relationship between propagation of lightning discharges and particles inside the cloud using the low frequency band 3-dimensional lightning location system and multi-parameter phased array weather radar. We visualized a bidirectional propagation that started the discharge in the boundary between ice-crystal and graupel areas (an altitude of 9 km) and then proceeded to split into the upper part of the ice-crystal region (an altitude of 12 km) and the upper part of the graupel region (an altitude of 7 km). Furthermore, in the case involving cloud-to-ground lightning, the discharge initiation altitude was relatively low at about 6 km, and the lightning channel was observed to propagate avoiding the multiple graupel regions in the cloud.

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There have been many reports on pre-earthquake electromagnetic radiation in LF band. However, they are mostly investigated in the intensity of narrow band pulses and there are less discussion on source location. Therefore, we are developing an LF broadband interferometer capable to waveform and spatio-temporal estimation of electromagnetic radiation sources using capacitive circular flat plate antennas. In this paper, preliminary results in waveform analysis, a case study on relationship between unusual waveform and local moderate earthquakes, and performance of interferometer are demonstrated. Analysis of the waveform data observed by the interferometer elements showed that the system successfully recorded LF/VLF waveform signals caused by cloud-to-ground discharges. LF band signals different from the above waveforms were also detected. Although it is possible that these signals were caused by intracloud discharges, we found that we cannot dismiss the possibility that these signals were related to earthquakes.

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