Modelling the production of terrestrial gamma-ray flashes during the final leader step

Christoph Köhn; Olivier Chanrion; Heumesser Matthias; Krystallia Dimitriadou; Torsten Neubert

doi:https://doi.org/10.5194/egusphere-egu2020-4645

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[Back] [Session NH1.3]

EGU2020-4645

https://doi.org/10.5194/egusphere-egu2020-4645

EGU General Assembly 2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Modelling the production of terrestrial gamma-ray flashes during the final leader step

Christoph Köhn, Olivier Chanrion, Heumesser Matthias, Krystallia Dimitriadou, and Torsten Neubert

Christoph Köhn et al.

Technical University of Denmark, DTU Space, Astrophysics & Atmospheric Science, Lyngby, Denmark (koehn@space.dtu.dk)

Recent measurements by the Atmosphere-Space Interactions Monitor (ASIM) indicate that the production of energetic electrons and of subsequent terrestrial gamma-ray flashes (TGFs) occurs immediately prior to intracloud lightning breakdown. Inspired by this finding, we relate the production of high-energy particles to the occurrence of streamer coronas initiated during the final leader step when the leader is in the vicinity of the upper cloud charge layer. Therefore, we model the acceleration of electrons and the subsequent production of energetic photons in the electric fields of the two encountering streamer coronas which are initiated in the vicinity of the leader tip and of the charge layer. Applying a particle Monte Carlo code, we first initiate thermal electrons in the electric field of the leader tip and subsequently turn on the streamer coronas and simulate the acceleration of electrons from thermal energies to energies of several tens of MeV. We present the temporal evolution of the electron and photon energies and spectra, and discuss the role of the electric fields of the encountering streamer coronas. Finally, we relate our results to ASIM measurements and discuss the duration and the relative timing of TGF bursts.

How to cite: Köhn, C., Chanrion, O., Matthias, H., Dimitriadou, K., and Neubert, T.: Modelling the production of terrestrial gamma-ray flashes during the final leader step, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4645, https://doi.org/10.5194/egusphere-egu2020-4645, 2020

Comments on the presentation

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Presentation version 1 – uploaded on 01 May 2020

CC1:
Comment on EGU2020-4645, Paul Connell, 04 May 2020
What is the expected altitude of the positive charge and corona ?
- AC1: Reply to CC1, Christoph Köhn, 04 May 2020
  Dear Paul
  The lightning leader tip is located at 10 km altitude; thus the upper charge layer is at 10.1 km altitude.

CC2:
Comment on EGU2020-4645, Pavlo Kochkin, 04 May 2020
Hi Chris. In the "final-leader-step" assumption for TGF production, how would you explaine the multipulse TGFs?
- AC2: Reply to CC2, Christoph Köhn, 04 May 2020
  Hoi Pavlo
  This is a very good question. I do have some thoughts about it, but I would like to not share this right now right here since that would be rather speculative. This is something for future research which I am happy to discuss later at some point.

CC3:
Comment on EGU2020-4645, Alexander Kostinskiy, 04 May 2020
Hello everyone, what mechanism do you use to initiate positive streamer flashes from the edge of a positive charge?
What is the charge and spatial distribution of the charge of these flares?
Why do you take such a high speed of the negative leader, which, as I understand it, is not measured at these high altitudes?
- AC3:
  Reply to CC3, Christoph Köhn, 05 May 2020
  Dear Alexander
  The streamer coronas are initiated by the electrons distributed between the leader tip and the upper charge layer.
  The spatial distribution is determined by the velocity v_{\pm}; a sketch on how the coronas evolve is given in slide 9 showing the electric fields of the coronas. We do not model the evolution of the charge density, but rather the evolution of the electric field.
  In fact, the leader is stationary (waiting to take his final step); we here concentrate on the evolution of the streamer coronas. Here, the used velocities are well in agreement with experiments.
  - CC4: Reply to AC3, Alexander Kostinskiy, 05 May 2020
    Dear Christoph,
    I probably poorly formulated the question. Due to what process are streamer flashes in the region of a positive charge initiated? The geometry of streamer flashes and the frequency of their appearance depend on this. If streamer outbreaks appear periodically, then you could, for example, explain the periodicity of TGF by this process. Maybe you think that two space charges are moving towards each other and you are not yet interested in how they were initiated?
    Regards,
    Alexander
    
    AC4: Reply to CC4, Christoph Köhn, 06 May 2020
    Dear Alexander
    Yes, you are right. The main idea here is rather about two space charge regions, which we identify with two streamer coronas, encountering each other. You are right that the way how they are initiated might change the properties of these streamer coronas. This is why we made an additional parameter study. The purpose here is to show that this set-up can explain the occurrence of TGFs with the correct properties. In the future, we will do a more in-depth study.
    Kind regards,
    Christoph