Observations of the Origin of Downward Terrestrial Gamma-Ray Flashes

Abstract

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.

arXiv commentTypo fixed and reference added. Manuscript is 36 pages. Supplemental Information is 42 pages. This paper is to be published in the Journal of Geophysical Research: Atmospheres. Online data repository: Open Science Framework DOI: 10.17605/OSF.IO/Z3XDA

References in corpus (7)

• The physics of streamer discharge phenomena
• The surface detector array of the Telescope Array experiment
• Gamma-ray Showers Observed at Ground Level in Coincidence With Downward Lightning Leaders
• Spontaneous emergence of space stems ahead of negative leaders in lightning and long sparks
• Pulse properties of terrestrial gamma-ray flashes detected by the Fermi Gamma-Ray Burst Monitor
• Characterizing upward lightning with and without a terrestrial gamma-ray flash
• TETRA Observation of Gamma Rays at Ground Level Associated with Nearby Thunderstorms

Cited by in corpus (7)

• The initial stage of cloud lightning imaged in high-resolution
• The First GECAM Observation Results on Terrestrial Gamma-ray Flashes and Terrestrial Electron Beams
• First High-speed Video Camera Observations of a Lightning Flash Associated with a Downward Terrestrial Gamma-ray Flash
• Determination of the Cosmic-Ray Chemical Composition: Open Issues and Prospects
• Multi-messenger observations of thunderstorm-related bursts of cosmic rays
• The Pierre Auger Exotic Events and Axion Quark Nuggets
• Analysis of Fluorescence Telescope Data Using Machine Learning Methods