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Winter Positive Cloud‐to‐Ground Lightning Flashes Observed by LMA in Japan

Using a lightning mapping array (LMA), we have observed 24 positive cloud‐to‐ground (CG) flashes occurred in three thunderstorm days. These flashes can be apparently grouped into 5 clusters according to their occurrence times. We have obtained the charge structures for both the individual flashes and clusters. It was found that 4 out of 5 clusters of positive CG flashes exhibited either inverter dipolar or tri‐polar charge structures. This result indicates that the high percentage of positive CG flashes in Hokuriku winter thunderstorms originated from the inverted charge structure rather than the various deformations of normal charge structures widely accepted in literatures. The flash positive charge appeared to distribute usually in a layer with its thickness of around 1 km, its horizontal area of more than 100 km2 and its bottom altitude of around 1–2 km above the ground. For each of the flash, we have also obtained its duration, length, duration before the first stroke and convex area. It was found that all flashes with a large peak return stroke current had short durations before their first return strokes. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.