ELFIN-GPS Comparison of Energetic Electron Fluxes: Modeling Low-Altitude Electron Flux Mapping to the Equatorial Magnetosphere

Abstract

Near-equatorial measurements of energetic electron fluxes, in combination with numerical simulation, are widely used for monitoring of the radiation belt dynamics. However, the long orbital periods of near-equatorial spacecraft constrain the cadence of observations to once per several hours or greater, that is, much longer than the mesoscale injections and rapid local acceleration and losses of energetic electrons of interest. An alternative approach for radiation belt monitoring is to use measurements of low-altitude spacecraft, which cover, once per hour or faster, the latitudinal range of the entire radiation belt within a few minutes. Such an approach requires, however, a procedure for mapping the flux from low equatorial pitch angles (near the loss cone) as measured at low altitude, to high equatorial pitch angles (far from the loss cone), as necessitated by equatorial flux models. Here we do this using the high energy resolution ELFIN measurements of energetic electrons. Combining those with GPS measurements we develop a model for the electron anisotropy coefficient, $n$, that describes electron flux $j_{\mathrm{trap}}$ dependence on equatorial pitch-angle, ${\alpha }_{eq}$, $j_{\mathrm{trap}}\sim {\sin }^n{\alpha }_{eq}$. We then validate this model by comparing its equatorial predictions from ELFIN with in-situ near-equatorial measurements from Arase (ERG) in the outer radiation belt.