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- Title
Analysis of Radiation Belt "Killer" Electron Energy Spectra.
- Authors
Summers, Danny; Stone, Sarah
- Abstract
Highly energetic (>1 MeV) electrons are typically generated in the Earth's outer radiation belt during geomagnetically disturbed times. Such "killer" electrons can be produced by electron cyclotron resonance with whistler‐mode waves. We model this process by a relativistic Fokker‐Planck diffusion equation for the electron distribution function f(E), where E is the normalized electron kinetic energy. The equation involves an energy diffusion coefficient D(E) and an advection coefficient A(E), which depend on the wave spectral energy density. For two types of wave energy spectrum, a Gaussian and a power law with spectral index q, we seek large‐E steady‐state solutions for f(E). For lower‐band chorus, for both Gaussian and power law spectra, we find that f∼e−E/k $f\sim {e}^{-E/\sqrt{k}}$ with k = D0T0, where D0 is a diffusion parameter and T0 is the e‐folding timescale for electron loss. For a full‐band whistler spectrum, we find that if 2 < q < 4 then f∼e−2(4−q)E(4−q)/2k $f\sim {e}^{-\frac{2}{(4-q)}\frac{{E}^{(4-q)/2}}{\sqrt{k}}}$; in the special case q = 4, we obtain the power law solution f ∼ E−δ, where δ=(−1+9+4/k)/2 $\delta =(-1+\sqrt{9+4/k})/2$. We compare the analytical electron spectra obtained with the phase‐space density profiles observed by the Van Allen Probes. Key Points: Killer electron generation by chorus waves is modeled by a Fokker‐Planck diffusion equationLarge‐E asymptotic solutions for the electron energy spectra are derivedWe find good agreement between the asymptotic spectra and the experimental spectra from four killer electron "events"
- Subjects
RADIATION belts; CYCLOTRON resonance; ELECTRON kinetic energy; ELECTRON distribution; DISTRIBUTION (Probability theory); WAVE energy; ELECTRON diffusion; ADVECTION-diffusion equations
- Publication
Journal of Geophysical Research. Space Physics, 2022, Vol 127, Issue 9, p1
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2022JA030698