Journal article
The Characteristic Pitch Angle Distributions of 1 eV to 600 keV Protons Near the Equator Based On Van Allen Probes Observations
Journal of geophysical research. Space physics, Vol.122(9), pp.9464-9473
09/2017
DOI: 10.1002/2017JA024421
Abstract
Understanding the source and loss processes of various plasma populations is greatly aided by having accurate knowledge of their pitch angle distributions (PADs). Here we statistically analyze ~1 eV to 600 keV hydrogen (H+) PADs near the geomagnetic equator in the inner magnetosphere based on Van Allen Probes measurements, to comprehensively investigate how the H+ PADs vary with different energies, magnetic local times (MLTs), L shells, and geomagnetic conditions. Our survey clearly indicates four distinct populations with different PADs: (1) a pancake distribution of the plasmaspheric H+ at low L shells except for dawn sector; (2) a bidirectional field‐aligned distribution of the warm plasma cloak; (3) pancake or isotropic distributions of ring current H+; (4) radiation belt particles show pancake, butterfly, and isotropic distributions depending on their energy, MLT, and L shell. Meanwhile, the pancake distribution of ring current H+ moves to lower energies as L shell increases, which is primarily caused by adiabatic transport. Furthermore, energetic H+ (>10 keV) PADs become more isotropic following the substorm injections, indicating wave‐particle interactions. The radiation belt H+ butterfly distributions are identified in a narrow energy range of 100 < E < 400 keV at large L (L > 5), which are less significant during quiet times and extend from dusk to dawn sector through midnight during substorms. The different PADs near the equator provide clues of the underlying physical processes that produce the dynamics of these different populations.
Key Points
We performed a statistics of H+ PADs based on 4 years VAP data and identified four distinct populations in energy range of 1 eV to 600 keV
Plasmaspheric H+ shows pancake PADs at low L; warm plasma cloak are field aligned; more energetic H+ PADs depend on energy, MLT, and L shell
Energetic H+ PADs become more isotropic following the substorm injections, indicating wave‐particle interactions
Details
- Title: Subtitle
- The Characteristic Pitch Angle Distributions of 1 eV to 600 keV Protons Near the Equator Based On Van Allen Probes Observations
- Creators
- Chao Yue - University Corporation for Atmospheric ResearchJacob Bortnik - University of California, Los AngelesRichard M Thorne - University of California, Los AngelesQianli Ma - Boston UniversityXin An - University of California, Los AngelesC. R Chappell - Vanderbilt UniversityAndrew J Gerrard - New Jersey Institute of TechnologyLouis J Lanzerotti - New Jersey Institute of TechnologyQuanqi Shi - Shandong UniversityGeoffrey D Reeves - Los Alamos National LaboratoryHarlan E Spence - University of New HampshireDonald G Mitchell - Johns Hopkins University Applied Physics LaboratoryMatina Gkioulidou - Johns Hopkins University Applied Physics LaboratoryCraig A Kletzing - University of Iowa
- Resource Type
- Journal article
- Publication Details
- Journal of geophysical research. Space physics, Vol.122(9), pp.9464-9473
- DOI
- 10.1002/2017JA024421
- ISSN
- 2169-9380
- eISSN
- 2169-9402
- Number of pages
- 10
- Grant note
- NASA (NNX16AG21G; NAS5‐01072) NASA Living With a Star Jack Eddy Postdoctoral Fellowship Program NASA LWS (NNX13AI61G)
- Language
- English
- Date published
- 09/2017
- Academic Unit
- Physics and Astronomy
- Record Identifier
- 9984199829702771
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