Characteristics of Negative Flashes With Multiple Ground Strike Points Located by the Japanese Lightning Detection Network

Approximately 50% of natural lightning flashes make multiple contacts on the ground. Lightning-induced voltage by nearby lightning stroke is the major cause of overvoltage. The electromagnetic waves emitted by lightning flashes with multiple ground strike points (GSPs) increase new risks to damage electronics information devices located in the vicinity of the GSPs. Therefore, it is very important for electromagnetic compatibility engineering to clarify the characteristics of lightning flashes with multiple GSPs. We have observed lightning discharges over the whole area of Japan detected by the Japanese Lightning Detection Network (JLDN). Specifically, we analyzed negative cloud-to-ground (CG) flashes observed by JLDN within 80 km of Sagamihara in summer. We investigated the median location accuracy of the JLDN in the observation area to evaluate characteristics of spatial distribution of subsequent strokes hitting the GSPs. The median location accuracy varied between 0.2 and 0.4 km in the observed area. The mean multiplicity of negative CG flash observed by JLDN was 3.5. The average inter-stroke interval of new ground contact (NGC) strokes was longer than that of pre-existing channel (PEC) strokes. The ratio of peak current to the first return stroke was higher in the NGC than that in the PECs. Some of flashes hit the ground at several points. The mean number of GSPs was 2.0 per flash, with the mean number of 1.6 subsequent strokes per a GSP. Furthermore, the number of strokes per a GSP has not been previously reported. We also observed that the subsequent strokes altered between different GSPs.