Simulations of Stormtime Diffuse Aurora Using AMIE Electric Field and Flux-Dependent Electron Scattering Model

We obtain distributions of precipitating electrons by tracing drift shells of plasmasheet electrons in the limit of strong pitch angle diffusion in Dungey's model magnetosphere, which consists of a dipolar magnetic field plus a uniform southward field. Under strong pitch-angle diffusion particles drift so as to conserve an adiabatic invariant L equal to the enclosed phase-space volume (i.e., the cube of the particle momentum p times the occupied flux-tube volume per unit magnetic flux). Here we model the magnetospheric convection electric field by mapping an analytical expansion of the AMIE (Assimilative Model of Ionospheric Electrodynamics) ionospheric potential (a function of latitude and magnetic local time) along magnetic field lines from ionospheric latitudes >= 50° (L >= 2.5) in Dungey's magnetic field model. We trace the bounce-averaged drift motions of representative plasmasheet electrons with values of L corresponding to kinetic energies of 0.25-64 keV on a field line of equatorial radius r = 6 R_E, which maps to 65° latitude in the ionosphere. Using the simulation results, we map stormtime phase space distributions along particle drift shells, taking into account loss due to precipitation. We consider 3 models of electron scattering: (1) the limit of strong scattering everywhere, (2) an MLT-dependent scattering that is less than everywhere strong in the plasma sheet, and (3) an electron flux-dependent scattering. Our flux-dependent scattering model is based on the Kennel-Petschek concept that wave growth occurs where there is sufficient electron flux to cause it. From the phase space distributions thus obtained, we calculate the precipitating electron energy flux into the ionosphere. For this study we focus on the main phase of the October 19, 1998, storm. Magnitudes of the integrated electron energy flux obtained from our simulations are consistent with statistical averages of precipitating electron flux obtained from NOAA data. For selected times of interest we compare the simulated electron flux with Polar UVI images. We also weight our simulated electron flux by the Bremsstrahlung X-ray production curve to obtain simulated X-ray fluxes for comparison with PIXIE images. Our simulations with the electron flux-dependent scattering model indeed reproduce some of the features that are observed in UVI and X-ray images.