[P-EM11] Dynamics of the Inner Magnetospheric System

[PEM11-05] Effective energy range of electrons exciting whistler-mode chorus emissions in the inner magnetosphere

*Yoshiharu Omura¹, Takeshi Nogi¹ (1.Reserach Institute for Sustainable Humanosphere, Kyoto University)

Keywords:wave-particle interaction, radiation belts, nonlinear process

Whistler-mode chorus emissions are frequently observed outside the plasmapause, and they control the dynamics of energetic electrons including relativistic electrons of the outer radiation belt. Chorus emissions are generated through nonlinear cyclotron resonance with energetic electrons with temperature anisotropy [1]. The nonlinear process is started from a triggering wave growing from thermal fluctuations with the maximum linear growth rate or a triggering wave artificially injected in the equatorial region. We have conducted electromagnetic particle simulations reproducing chorus emissions from a triggering wave injected at the equator with different frequencies and parameters. We find the generation of subpackets of chorus emissions with rising-tone frequency at slightly different locations near the magnetic equator. The generation region moves upstream or downstream depending on frequencies of the triggering wave. We have found that the generation of subpackets moves with the source velocity which is a sum of the group velocity and the resonance velocity [2]. Especially when the source velocity is slightly negative, a long rising-tone subpacket is generated through formation of an electron hole in velocity phase space stretched over the equator. The long rising-tone emission is very effective in accelerating electrons to relativistic energies in a short time [3]. The condition for the small negative source velocity can determine the effective energy ranges of electrons that can generate chorus emissions in the magnetosphere.

References:
[1] Y. Omura (2021), Nonlinear wave growth theory of whistler-mode chorus and hiss emissions in the magnetosphere, Earth Planets Space 73, 95.
[2] T. Nogi, and Y. Omura (2022), Nonlinear signatures of VLF-triggered emissions: A simulation study, Journal of Geophysical Research: Space Physics, 127, e2021JA029826.
[3] J.C. Foster, P.J. Erickson, Y. Omura (2021), Subpacket structure in strong VLF chorus rising tones: characteristics and consequences for relativistic electron acceleration, Earth, Planets and Space 73, 140.