An Empirical Model of Radiation Belt Electron Pitch Angle Distributions Based On Van Allen Probes Measurements

Journal Article · Tue Apr 17 00:00:00 EDT 2018 · Journal of Geophysical Research. Space Physics

DOI:https://doi.org/10.1029/2018JA025277· OSTI ID:1485406

Zhao, H. ^[1]; Friedel, R. H. W. ^[2]; Chen, Y. ^[3]; Reeves, G. D. ^[2]; Baker, D. N. ^[1]; Li, X. ^[1]; Jaynes, A. N. ^[1]; Kanekal, S. G. ^[4]; Claudepierre, S. G. ^[5]; Fennell, J. F. ^[5]; Blake, J. B. ^[5]; Spence, H. E. ^[6]

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1. Univ. of Colorado, Boulder, CO (United States). Lab. for Atmospheric and Space Sciences
2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); The New Mexico Consortium, Los Alamos, NM (United States)
3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
4. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
5. The Aerospace Corporation, El Segundo, CA (United States). Space Sciences Dept.
6. Univ. of New Hampshire, Durham, NH (United States). Inst. for the Study of Earth, Oceans, and Space

Based on over 4 years of Van Allen Probes measurements, an empirical model of radiation belt electron equatorial pitch angle distribution (PAD) is constructed here. The model, developed by fitting electron PADs with Legendre polynomials, provides the statistical PADs as a function of L-shell (L = 1–6), magnetic local time, electron energy (~30 keV to 5.2 MeV), and geomagnetic activity (represented by the Dst index) and is also the first empirical PAD model in the inner belt and slot region. For megaelectron volt electrons, model results show more significant day-night PAD asymmetry of electrons with higher energies and during disturbed times, which is caused by geomagnetic field configuration and flux radial gradient changes. Steeper PADs with higher fluxes around 90° pitch angle and lower fluxes at lower pitch angles for higher-energy electrons and during active times are also present, which could be due to electromagnetic ion cyclotron wave scattering. For hundreds of kiloelectron volt electrons, cap PADs are generally present in the slot region during quiet times and their energy-dependent features are consistent with hiss wave scattering, while during active times, cap PADs are less significant especially at outer part of slot region, which could be due to the complex energizing and transport processes. Finally, the 90°-minimum PADs are persistently present in the inner belt and appear in the slot region during active times, and minima at 90° pitch angle are more significant for electrons with higher energies, which could be a critical evidence in identifying the underlying physical processes responsible for the formation of 90°-minimum PADs.

• Research Organization: Los Alamos National Lab. (LANL), Los Alamos, NM (United States); NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States); Univ. of Colorado, Boulder, CO (United States)
• Sponsoring Organization: National Aeronautics and Space Administration (NASA) (United States); USDOE
• Grant/Contract Number: 89233218CNA000001
• OSTI ID: 1485406
• Report Number(s): LA-UR--18-25083
• Journal Information: Journal of Geophysical Research. Space Physics, Journal Name: Journal of Geophysical Research. Space Physics Journal Issue: 5 Vol. 123; ISSN 2169-9380
• Publisher: American Geophysical Union
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
empirical model
geomagnetic storms
inner belt and slot region
pitch angle distribution
radiation belt electrons