Energetic electron precipitation induced by oblique whistler mode chorus
emissions
Abstract
Energetic electron accelerations and precipitations in the Earth’s outer
radiation belt are highly associated with wave-particle interactions
between whistler mode chorus waves and electrons. We perform test
particle simulation to investigate the electron behaviors interacting
with both parallel and obliquely propagating chorus emissions at L=4.5.
We build up a database of the Green’s functions, which are treated as
results of the input electrons interacting with one emission, for a
large number of electrons interacting with whistler mode chorus
emissions. The loss process of electron fluxes interacting with
consecutive chorus emissions in the outer radiation belt are traced by
applying the convolution integrals of distribution functions and the
Green’s functions. Oblique chorus emissions lead to more electron
precipitation than that led by parallel chorus emissions. By checking
the resonance condition and resonant energy at loss cone angle, we find
that electrons are hardly dropped into the loss cone directly by Landau
resonance. The nonlinear scattering via cyclotron resonance is the main
process that pushes energetic electrons into the loss cone. We propose a
2-step precipitation process for oblique chorus emissions that
contributes to more electron loss: (1) During the first chorus emission,
the nonlinear trapping of Landau resonance moves an electron near the
loss cone. (2) During the second emission, the nonlinear scattering of
cyclotron resonance scatters the electron into the loss cone. The
combination of Landau resonance by oblique chorus emissions and
cyclotron resonance results in the higher precipitation rate than the
single cyclotron resonance by purely parallel chorus emissions.