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

Abstract

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. Here, 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.

Authors:
 [1];  [1];  [2];  [2];  [1];  [3];  [4]
  1. Univ. of Michigan, Ann Arbor, MI (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. West Virginia Univ., Morgantown, WV (United States)
  4. Univ. of Minnesota, Minneapolis, MN (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
National Aeronautic and Space Administration (NASA); USDOE
OSTI Identifier:
1291224
Report Number(s):
LA-UR-15-29276
Journal ID: ISSN 2169-9380
Grant/Contract Number:
AC52-06NA25396
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Space Physics
Additional Journal Information:
Journal Name: Journal of Geophysical Research. Space Physics; Journal ID: ISSN 2169-9380
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Heliospheric and Magnetospheric Physics

Citation Formats

Sarno-Smith, Lois K., Liemohn, Michael W., Skoug, Ruth M., Larsen, Brian Arthur, Moldwin, Mark B., Katus, Roxanne M., and Wygant, John R. Local time variations of high-energy plasmaspheric ion pitch angle distributions. United States: N. p., 2016. Web. doi:10.1002/2015JA022301.
Sarno-Smith, Lois K., Liemohn, Michael W., Skoug, Ruth M., Larsen, Brian Arthur, Moldwin, Mark B., Katus, Roxanne M., & Wygant, John R. Local time variations of high-energy plasmaspheric ion pitch angle distributions. United States. doi:10.1002/2015JA022301.
Sarno-Smith, Lois K., Liemohn, Michael W., Skoug, Ruth M., Larsen, Brian Arthur, Moldwin, Mark B., Katus, Roxanne M., and Wygant, John R. Fri . "Local time variations of high-energy plasmaspheric ion pitch angle distributions". United States. doi:10.1002/2015JA022301. https://www.osti.gov/servlets/purl/1291224.
@article{osti_1291224,
title = {Local time variations of high-energy plasmaspheric ion pitch angle distributions},
author = {Sarno-Smith, Lois K. and Liemohn, Michael W. and Skoug, Ruth M. and Larsen, Brian Arthur and Moldwin, Mark B. and Katus, Roxanne M. and Wygant, John R.},
abstractNote = {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. Here, 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.},
doi = {10.1002/2015JA022301},
journal = {Journal of Geophysical Research. Space Physics},
number = ,
volume = ,
place = {United States},
year = {Fri Jul 01 00:00:00 EDT 2016},
month = {Fri Jul 01 00:00:00 EDT 2016}
}

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Cited by: 4works
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  • Ion pitch angle distributions, measured in a near-synchronous orbit, are predominantly field aligned at low energies and predominantly peaked perpendicular to the magnetic field at higher energies. The transition from field-aligned fluxes to fluxes peaked predominantly perpendicular to the magnetic field occurs over a narrow energy range. These ion distributions have been observed at all local times between 5.3 and 7.8 R/sub E/. This transition energy correlates with the deep minimum observed in the ion spectra. There is no apparent correlation between the ion transition energy and magnetic local time, L, Kp, or Dst. However, the transition energy does respondmore » to observed particle injections. The transition energy decrease prior to injection, increases abruptly at injection by as much as 10--20 keV, and then decreases slowly after injection, increases abruptly at injection by as much as 10--20 keV, and then over several hours to instrument threshold level. Ion drift trajectory calculations indicate that the low-energy component below the transition energy drifts in from the nightside plasma sheet via local morning to the dayside. The high-energy component, above the transition energy, arrives on the dayside via local evening.« less
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  • Observations of low-energy ionospheric ions by the plasma composition experiment abroad ISEE 1 often show conical pitch angle distributions, that is, peak fluxes between 0/sup 0/ and 90/sup 0/ to the directions parallel or antiparallel to the magnetic field. Frequently, all three primary ionospheric ion species (H/sup +/, He/sup +/, and O/sup +/) simultaneously exhibit conical distributions with peak fluxes at essentially the same pitch angle. A distinction is made here between unidirectional, or streaming, distributions, in which ions are traveling essentially from only one hemisphere, and symmetrical distributions, in which significant fluxes are observed traveling from both hemispheres. Themore » orbital coverage for this survey was largely restricted to the night sector, approximately 2100--0600 LT, and moderate geomagnetic latitudes of 20/sup 0/--40/sup 0/. Also, lack of complete pitch angle coverage at all times may have reduced detection for conics with small cone angles. However, we may conclude that the unidirectional conical distributions observed in the northern hemisphere are always observed to be traveling from the northern hemisphere and that they exhibit the following characteristics relative to the symmetric distributions, in that they (1) are typically observed on higher L shells (that is, higher geomagnetic latitudes or larger geocentric distances or both), (2) tend to have significantly larger cone angles, and (3), are associated with higher magnetic activity levels.« less
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