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