Observations of the Origin of Downward Terrestrial Gamma-Ray Flashes
Observations of the Origin of Downward Terrestrial Gamma-Ray Flashes
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DOI：
10.1029/2019jd031940
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发表时间：
2020-12-16
影响因子：
4.4
通讯作者：
Zundel, Z.
中科院分区：
文献类型：
--
作者：
Belz, J. W.;Krehbiel, P. R.;Zundel, Z.
在本文中，我们报告的第一个密切的，高分辨率的观测向下定向地面伽玛射线闪光（TGFs）检测的大面积望远镜阵列宇宙射线天文台，结合宽带VHF干涉仪和快速电场变化测量的母放电。结果表明，TGFs发生在强烈的初始击穿脉冲（IBP）的负云到地面和低海拔云内闪光的前几毫秒和IBP是由一个新确定的流光放电过程称为快速负击穿。观测结果表明，负责产生TGFs的相对论性逃逸电子雪崩（RREAs）是由快速流光系统内的嵌入式火花状瞬态传导事件（TCEs）发起的，也可能是由单个快速流光本身发起的。TCE被推断为是经典IBP sferics的特征的脉冲子脉冲的原因。雪崩的进一步发展将通过在快速负击穿的前进前沿之前增强的电场来促进。除了显示IBP及其神秘的子脉冲的性质外，观测还为未解决的问题提供了一种可能的解释，即在初始负击穿期间如何发生拖缆到先导的过渡，即作为连续IBP的最后阶段中流动的强电流的结果，向后延伸通过IBP本身和IBP之前的负拖缆击穿。
In this paper we report the first close, high-resolution observations of downward-directed terrestrial gamma-ray flashes (TGFs) detected by the large-area Telescope Array cosmic ray observatory, obtained in conjunction with broadband VHF interferometer and fast electric field change measurements of the parent discharge. The results show that the TGFs occur during strong initial breakdown pulses (IBPs) in the first few milliseconds of negative cloud-to-ground and low-altitude intracloud flashes and that the IBPs are produced by a newly identified streamer-based discharge process called fast negative breakdown. The observations indicate the relativistic runaway electron avalanches (RREAs) responsible for producing the TGFs are initiated by embedded spark-like transient conducting events (TCEs) within the fast streamer system and potentially also by individual fast streamers themselves. The TCEs are inferred to be the cause of impulsive sub-pulses that are characteristic features of classic IBP sferics. Additional development of the avalanches would be facilitated by the enhanced electric field ahead of the advancing front of the fast negative breakdown. In addition to showing the nature of IBPs and their enigmatic sub-pulses, the observations also provide a possible explanation for the unsolved question of how the streamer to leader transition occurs during the initial negative breakdown, namely, as a result of strong currents flowing in the final stage of successive IBPs, extending backward through both the IBP itself and the negative streamer breakdown preceding the IBP.