Characterization and Evolution of Radiation Belt Electron Energy Spectra Based on the Van Allen Probes Measurements. Issue 6 (20th June 2019)

• Record Type: Journal Article
• Authors: Zhao, H.; Johnston, W. R.; Baker, D. N.; Li, X.; Ni, B.; Jaynes, A. N.; Kanekal, S. G.; Blake, J. B.; Claudepierre, S. G.; Reeves, G. D.; Boyd, A. J.
• Is Part Of: Journal of geophysical research. Volume 124:Issue 6(2019)
• Page Start: 4217
• Page End: 4232
• Publication Date: 2019-06-20
• Subjects: radiation belt electrons -- energy spectrum -- exponential energy spectrum -- power law energy spectrum -- bump‐on‐tail energy spectrum -- plasmapause; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2019JA026697
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Based on the measurements of ~100‐keV to 10‐MeV electrons from the Magnetic Electron Ion Spectrometer (MagEIS) and Relativistic Electron and Proton Telescope (REPT) on the Van Allen Probes, the radiation belt electron energy spectra characterization and evolution have been investigated systematically. The results show that the majority of radiation belt electron energy spectra can be represented by one of three types of distributions: exponential, power law, and bump‐on‐tail (BOT). The exponential spectra are generally dominant in the outer radiation belt outside the plasmasphere, power law spectra usually appear at high L‐shells during injections of lower‐energy electrons, and BOT spectra commonly dominate inside the plasmasphere at L>2.5 during relatively quiet times. The main features of three types of energy spectra have also been revealed. Specifically, for the BOT energy spectrum, the energy of local flux maximum usually ranges from approximately hundreds of keV to several MeV and the energy of local flux minimum varies from ~100 keV to ~MeV, both increasing as L‐shell decreases, confirming the plasmaspheric hiss wave scattering to be the main mechanism forming the BOT energy spectra. Statistical results using 4‐year observations from the Van Allen Probes on the relation between energy spectra and plasmapause location also show that the plasmasphere plays a critical role in shaping radiation belt electron energy spectrum: the peak location of BOT energy spectra is ~1 L‐shell inside the minimum plasmapause, where BOT energy spectra mostly form in ~1–2 days as a result of hiss wave scattering. Key Points: Most radiation belt electron energy spectra can be represented by one of three distributions: exponential, power law, and bump‐on‐tail Exponential spectra dominate outside the plasmasphere; power law spectra often appear at high L during injections of lower‐energy electrons Bump‐on‐tail spectra dominate inside the plasmasphere at L<2.5 and are caused by hiss wave scattering