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Dominance of high‐energy (>150 keV) heavy ion intensities in Earth's middle to outer magnetosphere
Author(s) -
Cohen Ian J.,
Mitchell Donald G.,
Kistler Lynn M.,
Mauk Barry H.,
Anderson Brian J.,
Westlake Joseph H.,
Ohtani Shinichi,
Hamilton Douglas C.,
Turner Drew L.,
Blake J. Bernard,
Fennell Joseph F.,
Jaynes Allison N.,
Leonard Trevor W.,
Gerrard Andrew J.,
Lanzerotti Louis J.,
Allen Robert C.,
Burch James L.
Publication year - 2017
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2017ja024351
Subject(s) - magnetosphere , ion , physics , proton , solar wind , atomic physics , van allen radiation belt , helium , spectrometer , charged particle , plasma , nuclear physics , optics , quantum mechanics
Previous observations have driven the prevailing assumption in the field that energetic ions measured by an instrument using a bare solid state detector (SSD) are predominantly protons. However, new near‐equatorial energetic particle observations obtained between 7 and 12 R E during Phase 1 of the Magnetospheric Multiscale mission challenge the validity of this assumption. In particular, measurements by the Energetic Ion Spectrometer (EIS) instruments have revealed that the intensities of heavy ion species (specifically oxygen and helium) dominate those of protons at energies ≳ 150–220 keV in the middle to outer (>7 R E ) magnetosphere. Given that relative composition measurements can drift as sensors degrade in gain, quality cross‐calibration agreement between EIS observations and those from the SSD‐based Fly's Eye Energetic Particle Spectrometer (FEEPS) sensors provides critical support to the veracity of the measurement. Similar observations from the Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) instruments aboard the Van Allen Probes spacecraft extend the ion composition measurements into the middle magnetosphere and reveal a strongly proton‐dominated environment at L ≲ 6 but decreasing proton intensities at L ≳ 6 . It is concluded that the intensity dominance of the heavy ions at higher energies (>150 keV) arises from the existence of significant populations of multiply‐charged heavy ions, presumably of solar wind origin.