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

• Published in: Journal of geophysical research. Space physics 2016-07, Vol.121 (7), p.6234-6244
• Main Authors: Sarno‐Smith, Lois K., Liemohn, Michael W., Skoug, Ruth M., Larsen, Brian A., Moldwin, Mark B., Katus, Roxanne M., Wygant, John R.
• Format: Article
• Language: English
• Subjects: algorithm; Algorithms; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Classification; Counting; Depletion; Electric fields; Electric potential; Energy; Energy consumption; Energy measurement; Fluxes; Geomagnetic activity; Geomagnetism; Geophysics; Heliospheric and Magnetospheric Physics; Helium; Ion distribution; Ion flux; Ion fluxes; Ions; Low energy; Magnetic fields; magnetosphere; Oxygen; Pitch (inclination); Pitch angle; pitch angles; Plasma physics; plasmasphere; Probes; Sorting algorithms; Spacecraft; spacecraft potential corrections
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1002/2015JA022301

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. Key Points Developed new pitch angle sorting algorithm for Van Allen Probes Found 90 degree pitch angle population depletion in near‐Earth postmidnight sector Corrected low energy HOPE ion fluxes for spacecraft potential