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Equatorial Pitch Angle Distributions of 1–50 keV Electrons in Earth's Inner Magnetosphere: An Empirical Model Based on the Van Allen Probes Observations

Journal Article · · Journal of Geophysical Research. Space Physics
DOI:https://doi.org/10.1029/2020ja028322· OSTI ID:1856148
 [1];  [2];  [2];  [3];  [3];  [3];  [4];  [2];  [2];  [4];  [5]
  1. Univ. of Colorado, Boulder, CO (United States); Auburn Univ., AL (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  3. Univ. of Colorado, Boulder, CO (United States)
  4. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); The New Mexico Consortium, Los Alamos, NM (United States)
  5. Aerospace Corporation, Chantilly, VA (United States)
+ Show Author Affiliations
Using 7 years of data from the Helium, Oxygen, Proton, and Electron instrument on the Van Allen Probes, equatorial pitch angle distributions (PADs) of 1–50 keV electrons in Earth's inner magnetosphere are investigated statistically. An empirical model of electron equatorial PADs as a function of radial distance, magnetic local time, geomagnetic activity, and electron energy is constructed using the method of Legendre polynomial fitting. Model results show that most equatorial PADs of 1–10s of keV electrons in Earth's inner magnetosphere are pancake PADs, and the lack of butterfly PADs is likely due to their relatively flat or positive flux radial gradients at higher altitudes. During geomagnetically quiet times, more anisotropic distributions of 1–10s of keV electrons at dayside than nightside are observed, which could be responsible for moderate chorus wave activities at dayside during quiet times as reported by previous studies. During active times, the anisotropy of 1–10s of keV electrons significantly enhances, consistent with the enhanced chorus wave activity during active times and suggesting the critical role of 1–10s of keV electrons in generating chorus waves in Earth's inner magnetosphere. Different enhanced anisotropy patterns of different energy electrons are also observed during active times: at R > ~4 RE, keV electrons are more anisotropic at dawn to noon, while 10s of keV electrons have larger anisotropy at midnight to dawn. Furthermore, these differences, combined with the statistical distribution of chorus waves shown in previous studies, suggest the differential roles of electrons with different energies in generating chorus waves with different properties.
Research Organization:
Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
Sponsoring Organization:
NASA
Grant/Contract Number:
89233218CNA000001
OSTI ID:
1856148
Report Number(s):
LA-UR-20-28894
Journal Information:
Journal of Geophysical Research. Space Physics, Journal Name: Journal of Geophysical Research. Space Physics Journal Issue: 1 Vol. 126; ISSN 2169-9380
Publisher:
American Geophysical UnionCopyright Statement
Country of Publication:
United States
Language:
English

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