Statistical Analysis on Plasmatrough Exohiss Waves From the Van Allen Probes

Abstract

AbstractIn this study using Van Allen Probe wave observations we investigate the statistical properties of exohiss waves, which are structureless whistler mode waves observed outside the plasmapause. The exohiss waves are identified based on the cold electron number density, frequency distribution, ellipticity, and wave normal angle. The statistical analysis on exohiss wave properties shows that exohiss waves prefer to occur over 3<L<6 from dawnside to noon and duskside during geomagnetic quiet times, and their wave power is larger at smaller values of L shell. The frequency of exohiss mainly ranges from 200 to 300 Hz and is almost independent of L shell. The median values of ellipticity and electromagnetic planarity of exohiss waves are 0.91 and 0.54, respectively. Furthermore, the equatorward Poynting flux is comparable to the poleward Poynting flux at the equator and it becomes dominant at the absolute value of the magnetic latitude |λ|∼20°. Our observation results reveal the statistical features of exohiss waves for the first time and support the exohiss formation mechanism that exohiss originates from plasmaspheric hiss leakage. The results demonstrate exohiss as an important energy dissipation route for plasmaspheric hiss and significantly improve the understanding of plasmaspheric hiss evolution in the radiation belt region.