Modeling Pitch Angle Distributions in the Slot Region and Inner Zone

Abstract:

"Peculiar" pitch angle distributions, with maxima near 70 - 80 degrees and a minimum at 90,
have been observed by MagEIS experiment on the Van Allen Probes satellites over a broad range
of energies spanning several hundred keV. These distributions are observed near L=2 and thus
it is unlikely that they are due to drift shell splitting. Here we test the hypothesis that
these distributions are produced by fast magnetosonic waves, whose electron energy diffusion rates
increase at pitch angles of 70-80 degrees. Using models for plasmaspheric hiss, lightning,
VLF transmitters and magnetosonic waves, we present time dependent simulations showing the evolution
of the electron distribution function. Our results show that magnetosonic waves are a likely candidate
for producing the observed pitch angle distributions. Our results suggest that wave acceleration
extends deep into the slot region of the magnetosphere. We discuss the implications of these results
and the need to better quantify the amplitude of magnetosonic waves at low L.