SM013-02
Study of the dynamics of energetic electrons scattered into the loss cone by coherent whistler-mode waves

Tuesday, 8 December 2020: 19:05
Virtual
Genki Ishizawa1, Yuto Katoh1, Masahiro Kitahara2, Atsushi Kumamoto1, Tomoki Kimura3 and Yohei Kawazura3, (1)Tohoku University, Sendai, Japan, (2)ISEE, Nagoya University, Nagoya, Japan, (3)Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, Sendai, Japan
Recorded Presentation
Abstract:
Whistler mode chorus emissions play important roles in the pitch angle scattering process of energetic electrons. Conventionally, the pitch angle scattering of energetic electrons has been considered as a diffusion process based on the quasi-linear theory. On the other hand, Kitahara and Katoh (2019) has theoretically and numerically revealed that coherent whistler-mode waves effectively trap small pitch angle electrons and change their pitch angle away from the loss cone. Further investigation for the detailed process of the pitch angle scattering by chorus emissions has been required.

To clarify the physical process of scattering electrons into the loss cone, we carry out test particle simulations, using the code developed by Kitahara and Katoh (2019). We assume coherent whistler-mode waves having the wave frequency of 0.3 Ωeq, where Ωeq is the electron gyrofrequency at the magnetic equator, with the wave amplitude of 0.01% ~ 0.1% of the background magnetic field intensity at the equator (B0eq). We also assume that the plasma frequency is equal to 4 Ωeq and is uniform along a field line.

Simulation results indicate that electrons are scattered into the loss cone by 2 types of the nonlinear pitch angle scattering processes; resonant scattering and non-resonant scattering. Resonant scattering decreases electrons’ pitch angle greatly. Non-resonant scattering contributes electrons having their initial pitch angle of a few degrees larger than the loss cone. For the case of the wave amplitude of 0.1% of B0eq, we show that electrons from about 15 to 20 degree for 20 keV are scattered into the loss cone by the resonant nonlinear scattering. As the wave amplitude become large, the number of electrons scattered into the loss cone by the non-resonant scattering increases. We also show the increase of the number of electrons scattered into the loss cone from the larger pitch angle range by the resonant scattering. Based on the simulation results, we discuss roles of nonlinear effects in the pitch angle scattering of energetic electrons.

References

[1] Kitahara, M., & Katoh, Y. (2019). Anomalous trapping of low pitch angle electrons by coherent whistler mode waves. Journal of Geophysical Research: Space Physics, 124, 5568–5583. doi:10.1029/2019JA026493

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