Radio Interferometer Observations of an Energetic in‐Cloud Pulse Reveal Large Currents Generated by Relativistic Discharges
Radio Interferometer Observations of an Energetic in‐Cloud Pulse Reveal Large Currents Generated by Relativistic Discharges
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DOI：
10.1029/2020jd032603
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发表时间：
2020-09
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通讯作者：
J. Tilles;P. Krehbiel;M. Stanley;W. Rison;Ningyu Liu;F. Lyu;S. Cummer;J. Dwyer;S. Senay;H. Edens;Xiangpeng Fan;Robert G. Brown;Jennifer G. Wilson
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作者：
J. Tilles;P. Krehbiel;M. Stanley;W. Rison;Ningyu Liu;F. Lyu;S. Cummer;J. Dwyer;S. Senay;H. Edens;Xiangpeng Fan;Robert G. Brown;Jennifer G. Wilson
陆地伽马射线闪电的产生机制尚不完全清楚，相应的闪电活动和雷暴电荷结构的细节也尚未完全确定。在这里，我们检查了亚微秒VHF(14-88 MHz)射电干涉仪观测的247-kA峰值电流EIP，或能量在云中脉冲，一个可靠的射电信号的TGF子集。该脉冲由三个高幅度脉冲组成，持续≃60μS，在第二个(主)脉冲达到峰值。EIP发生在一次极不寻常的正极性星际闪电期间，因为最初向上的负先导传播特别快，并释放出高度集中的上部正风暴电荷。闪光是由一次高功率(46kW)的窄双极事件引发的，在≃向上3公里闪电发展后约3ms才发生闪电事件。在≃200mμS之前，发生了一次快速的6×106m/S向上负击穿，紧随其后的是一系列快速(107m/108m/S)向下然后向上的流光事件，每次持续10~20μS，重复释放大量的正电荷。尽管重复的流光序列似乎是EIP的一个特征，并可能参与了EIP的启动，但EIP SFERIC的进化独立于VHF产生活动，支持SFERIC是由相对论放电电流产生的观点。此外，主Sferic脉冲期间的相对论电流引发了一个在VHF功率(115 KW)可与最高功率NBE相媲美的类似NBE的强烈事件。
The production mechanism for terrestrial gamma ray flashes (TGFs) is not entirely understood, and details of the corresponding lightning activity and thunderstorm charge structure have yet to be fully characterized. Here we examine sub‐microsecond VHF (14–88 MHz) radio interferometer observations of a 247‐kA peak‐current EIP, or energetic in‐cloud pulse, a reliable radio signature of a subset of TGFs. The EIP consisted of three high‐amplitude sferic pulses lasting ≃60 μs in total, which peaked during the second (main) pulse. The EIP occurred during a normal‐polarity intracloud lightning flash that was highly unusual, in that the initial upward negative leader was particularly fast propagating and discharged a highly concentrated region of upper‐positive storm charge. The flash was initiated by a high‐power (46 kW) narrow bipolar event (NBE), and the EIP occurred about 3 ms later after ≃3 km upward flash development. The EIP was preceded ≃200 μs by a fast 6 × 106 m/s upward negative breakdown and immediately preceded and accompanied by repeated sequences of fast (107–108 m/s) downward then upward streamer events each lasting 10 to 20 μs, which repeatedly discharged a large volume of positive charge. Although the repeated streamer sequences appeared to be a characteristic feature of the EIP and were presumably involved in initiating it, the EIP sferic evolved independently of VHF‐producing activity, supporting the idea that the sferic was produced by relativistic discharge currents. Moreover, the relativistic currents during the main sferic pulse initiated a strong NBE‐like event comparable in VHF power (115 kW) to the highest‐power NBEs.