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The Characteristic Pitch Angle Distributions of 1 eV to 600 keV Protons Near the Equator Based On Van Allen Probes Observations

Journal Article · · Journal of Geophysical Research. Space Physics
DOI:https://doi.org/10.1002/2017JA024421· OSTI ID:1415430
 [1];  [2];  [2];  [3];  [2];  [4];  [5];  [5];  [6];  [7];  [8];  [9];  [9];  [10]
  1. UCLA, Los Angeles, CA (United States); Univ. Corp. for Atmospheric Research, Boulder, CO (United States)
  2. UCLA, Los Angeles, CA (United States)
  3. UCLA, Los Angeles, CA (United States); Boston, Univ., Boston, MA (United States)
  4. Vanderbilt Univ., Nashville, TN (United States)
  5. New Jersey Institute of Technology, Newark, NJ (United States)
  6. Shandong Univ., Weihai (China)
  7. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); New Mexico Consortium, Los Alamos, NM (United States)
  8. Univ. of New Hampshire, Durham, NH (United States)
  9. The Johns Hopkins Univ. Applied Physics Lab., Laurel, MD (United States)
  10. Univ. of Iowa, Iowa City, IA (United States)
+ Show Author Affiliations
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: a pancake distribution of the plasmaspheric H+ at low L shells except for dawn sector; a bidirectional field-aligned distribution of the warm plasma cloak; pancake or isotropic distributions of ring current H+; 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 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. In conclusion, the different PADs near the equator provide clues of the underlying physical processes that produce the dynamics of these different populations.
Research Organization:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
NASA; USDOE
Grant/Contract Number:
AC52-06NA25396
OSTI ID:
1415430
Report Number(s):
LA-UR--17-30360
Journal Information:
Journal of Geophysical Research. Space Physics, Journal Name: Journal of Geophysical Research. Space Physics Journal Issue: 9 Vol. 122; ISSN 2169-9380
Publisher:
American Geophysical UnionCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (3)

A Statistical Study of EMIC Waves Associated With and Without Energetic Particle Injection From the Magnetotail journal January 2019
Ion Heating by Electromagnetic Ion Cyclotron Waves and Magnetosonic Waves in the Earth's Inner Magnetosphere journal June 2019
Eastward Propagating Second Harmonic Poloidal Waves Triggered by Temporary Outward Gradient of Proton Phase Space Density: Van Allen Probe A Observation journal December 2019

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Related Subjects

58 GEOSCIENCES
H+ pitch angle distributions
Heliospheric and Magnetospheric Physics
bidirectional field aligned
plasmaspheric H+
radiation belt H+
ring current
warm plasma cloak