The amplitude decay with distance for return strokes and in-cloud pulses using lightning electromagnetic field pulses measured by JASA

The Jianghuai Area Sferic Array (JASA) is a local network which was originally deployed in eastern China to detect lightning activities. It was equipped to record VLF/LF electromagnetic fields of lightning with no-dead time at different time-synchronized stations and the 2D locations of lightning events were achieved by using the time of arrival technique with baselines of hundreds to thousands of kilometres. The strength of a lightning event was estimated from the signal amplitude measured remotely at a known distance following the predetermined distance decay relationship. Using electromagnetic field pulses recorded at different stations, we investigate the decay relationship of lightning ampli-tude with distance. Our results indicate that signal amplitudes for both lightning return stroke pulses and in-cloud pulses decay exponentially with distance D as D-b. The factor b for lightning in-cloud pulses is significantly less than that for lightning returns stroke pulses. It suggests that previous lightning location networks tend to overestimate the strength of an in-cloud pulse when applying the decay relationship extracted from return strokes.