The Evolution of Whistler Hiss‐Like Waves Across Plasmapause: Hiss to Exohiss

Abstract

Abstract The exohiss waves are hiss‐like whistler mode waves that occur outside plasmapause. Although these waves can cause the loss of radiation belt electrons ∼<MeV through resonant scattering, the formation and evolution processes of exohiss waves remain incompletely covered yet. In this letter, by virtue of measurement from Van Allen Probes and ray tracing simulation, we provide a direct observational evidence for the origin of exohiss waves. We analyze the evolution of power spectrum density of hiss‐like whistler waves during their propagation. The results suggest that exohiss waves originate from mixed result of hiss waves leaked out from different L shells inside the plasmapause. Additionally, we found that frequencies of exohiss waves are primarily below 700 Hz, it is probably because the hiss waves with higher frequencies experience more severe Landau damping. Our results significantly improve understanding of the evolution of whistler waves in radiation belts.