Local time variations of high-energy plasmaspheric ion pitch angle distributions

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

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Recent observations from the Van Allen Probes Helium Oxygen Proton Electron (HOPE) instrument revealed a persistent depletion in the 1–10 eV ion population in the postmidnight sector during quiet times in the 2 < L < 3 region. This study explores the source of this ion depletion by developing an algorithm to classify 26 months of pitch angle distributions measured by the HOPE instrument. We correct the HOPE low energy fluxes for spacecraft potential using measurements from the Electric Field and Waves (EFW) instrument. A high percentage of low count pitch angle distributions is found in the postmidnight sector coupled with a low percentage of ion distributions peaked perpendicular to the field line. A peak in loss cone distributions in the dusk sector is also observed. These results characterize the nature of the dearth of the near 90° pitch angle 1–10 eV ion population in the near-Earth postmidnight sector. This study also shows, for the first time, low-energy HOPE differential number fluxes corrected for spacecraft potential and 1–10 eV H+ fluxes at different levels of geomagnetic activity.

Original languageEnglish (US)
Pages (from-to)6234-6244
Number of pages11
JournalJournal of Geophysical Research: Space Physics
Issue number7
StatePublished - Jul 1 2016

Bibliographical note

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©2016. American Geophysical Union. All Rights Reserved.


  • algorithm
  • magnetosphere
  • pitch angles
  • plasmasphere
  • spacecraft potential corrections


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