Parallel Acceleration of Suprathermal Electrons Caused by Whistler‐Mode Hiss Waves

Abstract

AbstractSuprathermal electrons (~0.1–10 keV) in the inner magnetosphere are usually observed in a 90°‐peaked pitch angle distribution, formed due to the conservation of the first and second adiabatic invariants as they are transported from the plasma sheet. We report a peculiar field‐aligned suprathermal electron (FASE) distribution measured by Van Allen Probes, where parallel fluxes are 1 order of magnitude higher than perpendicular fluxes. Those FASEs are found to be closely correlated with large‐amplitude hiss waves and are observed around the Landau resonant energies. We demonstrate, using quasilinear diffusion simulations, that hiss waves can rapidly accelerate suprathermal electrons through Landau resonance and create the observed FASE population. The proposed mechanism potentially has broad implications for suprathermal electron dynamics as well as whistler mode waves in the Earth's magnetosphere and has been demonstrated in the Jovian magnetosphere.