Postmidnight depletion of the high-energy tail of the quiet plasmasphere

Lois K. Sarno-Smith, Michael W. Liemohn, Roxanne M. Katus, Ruth M. Skoug, Brian A. Larsen, Michelle F. Thomsen, John R. Wygant, Mark B. Moldwin

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

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 Kp 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. Key Points One to ten eV ion depletion in quiet time postmidnight sector Depletion varies by ion species not ordered by mass Strong diurnal variation in high-energy tail of plasmasphere

Original languageEnglish (US)
Pages (from-to)1646-1660
Number of pages15
JournalJournal of Geophysical Research: Space Physics
Volume120
Issue number3
DOIs
StatePublished - Mar 1 2015

Bibliographical note

Publisher Copyright:
©2015. American Geophysical Union. All Rights Reserved.

Keywords

  • ion composition
  • ionosphere
  • plasmasphere
  • postmidnight
  • quiet time magnetosphere

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