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Postmidnight depletion of the high‐energy tail of the quiet plasmasphere
Author(s) -
SarnoSmith Lois K.,
Liemohn Michael W.,
Katus Roxanne M.,
Skoug Ruth M.,
Larsen Brian A.,
Thomsen Michelle F.,
Wygant John R.,
Moldwin Mark B.
Publication year - 2015
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2014ja020682
Subject(s) - plasmasphere , ionosphere , physics , thermosphere , ion , plasma , quiet , local time , range (aeronautics) , atomic physics , electron , atmospheric sciences , langmuir probe , helium , magnetosphere , geophysics , astronomy , plasma diagnostics , materials science , nuclear physics , statistics , mathematics , quantum mechanics , composite material
The Van Allen Probes Helium Oxygen Proton Electron (HOPE) instrument measures the high‐energy tail of the thermal plasmasphere allowing study of topside ionosphere and inner magnetosphere coupling. We statistically analyze a 22 month period of HOPE data, looking at quiet times with a K p index of less than 3. We investigate the high‐energy range of the plasmasphere, which consists of ions at energies between 1 and 10 eV and contains approximately 5% of total plasmaspheric density. Both the fluxes and partial plasma densities over this energy range show H + is depleted the most in the postmidnight sector (1–4 magnetic local time), followed by O + and then He + . The relative depletion of each species across the postmidnight sector is not ordered by mass, which reveals ionospheric influence. We compare our results with keV energy electron data from HOPE and the Van Allen Probes Electric Fields and Waves instrument spacecraft potential to rule out spacecraft charging. Our conclusion is that the postmidnight ion disappearance is due to diurnal ionospheric temperature variation and charge exchange processes.