Anomalous Features of Electromagnetic Pulses Caused by Lightning Return Strokes During Winter Thunderstorms in Japan

Abstract

Electromagnetic pulses caused by lightning return strokes have been observed during the thunderstorms seasons both in summer and in winter to understand the physics of the lightning discharge. We notice that the signatures of electromagnetic pulses caused by negative lightning return strokes, which we have observed during summer, is not far from the typical signatures reported by other investigators. On the other hand we find that the signatures of electromagnetic pulses caused by the winter positive lightning return strokes are occasionally different from those of the summer negative return strokes. That means, the signatures detected by N-S and E-W magnetic loops are often different from each other. We believe this feature is due to the inclination of the channel of positive lightning return strokes. The video pictures which were recorded simultaneously with magnetic fields confirm our surmise.