A Case Study of Transversely Heated Low?Energy Helium Ions by EMIC Waves in the Plasmasphere

The Van Allen Probe A spacecraft observed strong ?0.5-Hz helium (He+) band and weak ?0.8-Hz hydrogen (H+) EMIC waves on April 17, 2018, at L = ?4.5–5.2, in the dawn sector, near magnetic equator, close to plasmapause. We examined low-energy ion fluxes by Helium Oxygen Proton Electron (HOPE) instrument onboard during wave interval found that He+ flux (<10 eV) enhancements occur nearly simultaneously with He-band H-band power a direction mostly perpendicular background field without significant H+ O+ variations. suggest cold ions (<1 are preferentially transversely heated up 10 eV through interaction inside plasmasphere. low-Earth orbit localized precipitations of energetic protons upper ionosphere subauroral latitudes footprint A. Our observations provide clear evidence play an important role overall dynamics inner magnetosphere, contributing high-energy particle loss energization.