Negative Excursion of Surface Electric Fields During Gamma‐Ray Glows in Winter Thunderstorms

Abstract

AbstractDuring the 2020–2021 winter season, we detected 6 gamma‐ray glows at Kanazawa University, Japan. Negative surface electric fields (E‐fields; in the sign convention of atmospheric electricity) were observed by a field mill during all the glow cases. In five of the six cases, the peak E‐field reached around −12 kV m−1, and the E‐field during the glow detection was the strongest in the interval including 3 hr before and after the detection time. Therefore, negative charges should have been dominant in the thunderclouds that produced the gamma‐ray glows, and electrons were probably accelerated and multiplied by the E‐fields between a predominantly negative charge layer and a localized positive charge layer below. In addition, we extracted 8 non‐detection cases in the 2020–2021 winter season, in which surface E‐fields were stronger than −12 kV m−1. In 5 of the 8 cases, radar echoes were inadequately developed, suggesting insufficient charge accumulation. On the other hand, the remaining 3 cases had well‐developed radar echoes, and there was no significant difference from the detection cases.