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[PEM11-16] Precipitation rates of energetic electrons interacting with parallel and oblique whistler mode chorus emissions in the magnetosphere
Keywords:energetic electron precipitation, nonlinear wave-particle interaction, whistler mode chorus emission, multiple resonances, oblique propagation
Whistler mode chorus emissions cause both acceleration and precipitation of radiation belt electrons. In this study, we build Green’s function sets for electrons interacting with different chorus emissions at around L=4.5 in the magnetosphere. A Green’s function is treated as a result of the input electrons interacting with one chorus emission in a test particle simulation.The different Green’s functions related to different wave models with various wave amplitudes and wave normal angles. We compute 3 kinds of amplitudes which are with the maximum wave magnetic field Bw, max = 50 pT, 300 pT, and 2.1 nT, and 4 different wave normal angles settings including parallel propagating waves, slightly oblique waves, and very oblique waves. We utilize these Green’s functions to analyze the precipitation rate for electrons at energies 10keV-6MeV and equatorial pitch angles above the loss cone angle 4.56 deg before interacting with an emission.
Our results show that wave amplitude is the most important factor that affects the precipitation rate. Generally, electrons can be scattered into the loss cone from a higher initial equatorial pitch angle by large-amplitude waves than by small-amplitude waves. In the cases with the same amplitude, we discuss precipitation rates with different resonances. For cyclotron resonance, which contributes to most of the electron precipitation, low energy electrons have a higher precipitation rate than high energy electrons due to a higher pitch angle scattering rate. In addition, the anomalous trapping effect [1] of cyclotron resonance is weaker in oblique cases than in parallel cases. We find that electron precipitation from 50 keV to a few hundred keV is higher in oblique cases than in parallel cases because of nonlinear trapping via Landau resonance. Finally, for n=-1 cyclotron resonance (n is the harmonic number), which especially occurs in the large amplitude and very oblique case, electrons can be precipitated from initial equatorial pitch angle > 50 deg around 100-200 keV via nonlinear trapping.
[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. https://doi.org/10.1029/2019JA026493
Our results show that wave amplitude is the most important factor that affects the precipitation rate. Generally, electrons can be scattered into the loss cone from a higher initial equatorial pitch angle by large-amplitude waves than by small-amplitude waves. In the cases with the same amplitude, we discuss precipitation rates with different resonances. For cyclotron resonance, which contributes to most of the electron precipitation, low energy electrons have a higher precipitation rate than high energy electrons due to a higher pitch angle scattering rate. In addition, the anomalous trapping effect [1] of cyclotron resonance is weaker in oblique cases than in parallel cases. We find that electron precipitation from 50 keV to a few hundred keV is higher in oblique cases than in parallel cases because of nonlinear trapping via Landau resonance. Finally, for n=-1 cyclotron resonance (n is the harmonic number), which especially occurs in the large amplitude and very oblique case, electrons can be precipitated from initial equatorial pitch angle > 50 deg around 100-200 keV via nonlinear trapping.
[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. https://doi.org/10.1029/2019JA026493