Simulations of Radio Emissions from TGFs
Abstract
The initiation mechanism of terrestrial gamma ray flashes (TGFs) is still under debate and the source of the seed runaway electrons that ignites the TGF in thunderstorms is poorly understood. Actually, two theories are under consideration to explain the production of TGFs: the relativistic feedback discharge mechanism [e.g., Dwyer JGR, 117, A02308, 2012] and the lightning leader cold runaway electron mechanism [e.g., Celestin and Pasko, JGR, 116, A03315, 2011; Babich et al, JGR, 120, 5087, 2015]. For the relativistic feedback discharge mechanism, backscattered X-rays and backward propagating positrons produce a positive feedback effect that amplifies the number of relativistic runaway electrons avalanches. The second mechanism involves the production of thermal runaway electrons by lightning leaders, possibly by streamer discharges located at the tip of a lightning leader. We know from observations that lightning leaders produce X-rays and runaway electrons [e.g., Dwyer et al., GRL, 32, L01803, 2005]. However, the mechanisms for leaders/streamers to produce runaway electrons with the necessary rates are still under investigation and so it is unclear if abundant runaway electrons can be generated for the production of TGFs [e.g., Babich et al, JGR, 120, 5087, 2015]. Lightning and TGFs both produce radio emissions [e.g., Dwyer and Cummer, JGR, 118, 3769, 2013; Lyu et al., GRL., 45, 2018]. The radio emissions are a powerful tool to study the physics of TGFs and can be used to infer the properties of the runaway electrons. In this work, we will apply a new improved version of a 3D particle in cell code developed by Dwyer [JGR, 117, A02308, 2012] that simulates the physics of a propagating realistic leader, runaway electrons, X and gamma rays, and radio emissions, to study TGFs produced by either mechanism and the associated radio emissions. We will investigate under a set of realistic thunderstorm electric field conditions how cold runaway electrons impact the properties of TGFs and their radio emissions in the framework of the feedback theory, and we will compare the modeling results with the observation data available in the literature. We will show how the two mechanisms maybe connected and we will help clarify the possible roles of cold runaway electrons and the X-ray/positron feedback mechanisms on the production of TGFs.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMAE31A..06I
- Keywords:
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- 3304 Atmospheric electricity;
- ATMOSPHERIC PROCESSESDE: 3324 Lightning;
- ATMOSPHERIC PROCESSESDE: 4301 Atmospheric;
- NATURAL HAZARDS