Realistic Modeling of Auroral Electron Precipitation Fluxes With Low-energy Tails

Details Realistic Modeling of Auroral Electron Precipitation Fluxes With Low-energy Tails Realistic Modeling of Auroral Electron Precipitation Fluxes With Low-energy Tails

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsa51e..05r&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SA51E-05

Physics

[0310] Atmospheric Composition And Structure / Airglow And Aurora, [2407] Ionosphere / Auroral Ionosphere, [2716] Magnetospheric Physics / Energetic Particles: Precipitating

Scientific paper

This paper presents a technique for more realistic calculations of precipitating auroral electron fluxes with low-energy tails. Most auroral calculations assume either Maxwellian or Gaussian distributions for precipitating auroral electrons. These distributions have negligible flux at low energies. However, measurements usually show substantial low-energy tails (< 100 eV) on the down going fluxes. These observed low energy fluxes are comparable to the up going fluxes and orders of magnitude larger than the model fluxes that result from pure Maxwellian or Gaussian distributions. Evans and Moore (1979) in their analysis of a rocket flight from Poker Flat, Alaska at 2254 LT February 1, 1978 found that the energy distribution of the lower energy electrons approached a power law, while the pitch angle distribution approached isotropy. They proposed that the symmetry between the down going and up going low-energy electron flux intensities shows that, at low energies, the down going electrons originate as backscattered and secondary electrons from the atmosphere. This paper shows that good agreement between measured and modeled low-energy precipitating fluxes can be obtained by simply reflecting the up going flux at the upper boundary of the model. This is easy to incorporate into the model because the energy range is divided into discrete energy bins and the solution proceeds from the highest energy bin down to the lowest energy bin. The up going flux at the upper boundary altitude from the previous higher energy bin can simply be added to the down going flux at the current energy bin. This reflection procedure not only produces good agreement between the magnitudes of the modeled and measured down going fluxes, it also produces approximate equality between the model low-energy up going and down going flux intensities as observed. The calculated fluxes agree well with the Evans and Moore (1979) Maxwellian type precipitating fluxes and also with Gaussian inverted-V type precipitating fluxes from the Fast Auroral Snapshot Explorer (FAST) satellite. Reference: Evans, D. S., and T. E. Moore, Precipitating Electrons Associated with the Diffuse Aurora: Evidence for Electrons of Atmospheric Origin in the Plasma Sheet, J. Geophys. Res., 84(A11), 6451-6457, doi:10.1029/JA084iA11p06451, 1979.

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