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

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.

Kim, Khan-Hyuk; Kwon, Hyuck-Jin; Lee, Junhyun; Jin, Ho; Seough, Jungjoon;

Published by: Journal of Geophysical Research: Space Physics      Published on: 02/2021

YEAR: 2021     DOI:

Van Allen Probes


Quasi Thermal Noise Spectroscopy for Van Allen Probes

Quasi thermal fluctuations in the Langmuir/upper-hybrid frequency range are pervasively observed in space plasmas including the radiation belt and the ring current region of inner magnetosphere as well as the solar wind. The quasi thermal noise spectroscopy may be employed in order to determine the electron density and temperature as well as to diagnose the properties of energetic electrons when direct measurements are not available. However, when employing the technique, one must carefully take the spacecraft orientation into account. The present paper takes the upper-hybrid and multiple harmonic\textemdashor (n + 1/2)fce\textemdashemissions measured by the Van Allen Probes as an example in order to illustrate how the spacecraft antenna geometrical factor can be incorporated into the theoretical interpretation. This method can in principle be applied to other spacecraft, including the Parker Solar Probe.

Yoon, Peter; Hwang, Junga; Kim, Hyangpyo; Seough, Jungjoon;

Published by: Journal of Geophysical Research: Space Physics      Published on: 04/2019

YEAR: 2019     DOI: 10.1029/2019JA026460

(n+1/2)fce; antenna geometry; Quasi-thermal; Radiation belt; Upper hybrid; Van Allen Probes