Leader Polarity‐Reversal Feature and Charge Structure of Three Upward Bipolar Lightning Flashes

Abstract

AbstractWe have analyzed three upward bipolar lightning flashes (UBLFs) that occurred in Japanese winter thunderstorms. Leader polarity‐reversal processes in three flashes share the same features. During the several tens of milliseconds (lightning A 56 ms, lightning B 21 ms, lightning C 67 ms) before the initiation of the polarity‐reversal leader, one branch of the preceding leader in bipolar flashes was nearly decayed while other branches of the preceding leader were still in propagation. Then the polarity‐reversal leader will be initiated at the end of the decayed branch of the preceding leader. Initial sources of the polarity‐reversal leader are characterized by relatively strong very high frequency power (average value in lightning A, B, and C 24, 18, and 14 dBW) and obvious upward progression. Two of the three upward lightning (lightning A and B) occurred at a normal dipolar charge structure, while the remaining one (lightning C) occurred at an inverted dipolar charge structure. Based on the common features of the polarity‐reversal leader and charge structure, we have proposed a scenario to interpret the process of upward bipolar lightning flashes.