The Strongest Negative Lightning Strokes in Winter Thunderstorms in Japan

Winter thunderstorms in Japan are well known for the frequent production of energetic positive cloud‐to‐ground (CG) lightning flashes. By contrast, strong negative CG flashes or negative return strokes in winter thunderstorms are largely unknown. In this study, we demonstrate that negative return strokes with peak currents larger than 150 kA (absolute value) in winter thunderstorms in Japan mostly produce electric field change waveforms that are different from those of normal return strokes. Due to their unusual waveforms, these strongest negative strokes have not been recognized as return strokes by the lightning research community. We further demonstrate that these strong negative return strokes are preceded by a fast downward negative leader with a short duration and strong peak current. We suggest that the fast and powerful downward negative leader may be associated with downward terrestrial gamma‐ray flashes. We also present evidence that these strong negative strokes are likely “superbolts” observed from space. Plain Language Summary The negative return stroke is the most well studied lightning discharge process. In this study, we demonstrate that negative return strokes with peak currents larger than 150 kA in winter thunderstorms in Japan mostly produce unique electric field change waveforms that are generally different from those of normal return strokes. Due to their unusual waveforms, these strongest negative strokes have not been recognized as return strokes by the lightning research community and may not be correctly identified by nationwide lightning location systems. Key Points Negative return strokes with peak currents larger than 150 kA in winter in Japan produce unusual electric field change waveforms These strongest negative return strokes are preceded by a fast downward negative leader with short duration and large peak current The preceding downward negative leader may be associated with downward terrestrial gamma‐ray flashes