A Statistical Study of Low-Energy Ion Flux Enhancements by EMIC Waves in the Inner Magnetosphere

Abstract We have studied the statistical properties of low-energy proton (H+) and helium (He+) ion flux enhancements associated with EMIC waves in the inner magnetosphere using Van Allen Probes data for 2013-2017. We identified 167 low-energy ion flux enhancements when the EMIC waves occurred in a He-band or in a multiple band (H-band and He-band) with strong He-band and weak H-band wave activity and found that most of them occurred from the noon to the premidnight sector near the magnetic equator just inside the plasmapause. Of 167 flux enhancement events, 68 exhibited only He+ flux enhancements, and 99 exhibited both H+ and He+ flux enhancements. The EMIC wave-associated flux enhancement events are mostly energized in the direction perpendicular to the background magnetic field. When both H+ and He+ fluxes are simultaneously enhanced, the H+ flux events have a peak energy distributed in the range of 2-100 eV, and the peak energies of the He+ flux events are distributed in the 2 eV to 600 eV range, implying that the helium ions are more energized than the protons. The peak energies of only He+ flux enhancement without H+ flux enhancement are mostly distributed in a lower energy range, 2-10 eV. The energization of H+ and He+ ions can be explained by a linear plasma flow associated with EMIC waves. We suggest that the wave-associated linear plasma motion is a likely mechanism to explain the observations. This article is protected by copyright. All rights reserved.