On the Use of Different Magnetic Field Models for Simulating the Dynamics of the Outer Radiation Belt Electrons During the October 1990 Storm

During geomagnetic storms, the magnetic field in the outer belt is known to be significantly distorted by the solar wind, such that the outer belt dynamics can be greatly impacted by the magnetic field topology. In this context, we develop a reduced Fokker-Planck code that includes the effects related to realistic magnetic field models (by using the existing dedicated LANLGeoMag library) through the steps of preprocessing, postprocessing, and, for the first time, during the computation of the reduced Fokker-Planck diffusion equation itself. We perform the solutions of the reduced Fokker-Planck equation in the framework of the geomagnetic storm that occurred from 9 October to 15 October 1990. With the use of Combined Release and Radiation Effects Satellite observations, the magnetic field model is shown to strongly affect the way of conciliating theory with observations (processing steps). More specifically, we explain analytically and numerically why the use of a dipole field can lead to misleading interpretations on the local enhancements (attributed to local acceleration) displayed by the electron distribution function, resulting in inaccurate simulations results at large L-shells. The consideration of a realistic field does not produce any artificial peaks. With such corrected data sets, a great part of the dynamics can be described by radial transport and is thus better reproduced by the simulations. This crucial importance of the field geometry is further emphasized with the calculation of unidirectional, omnidirectional, and integral electron fluxes, and their accuracy is quantified thanks to dedicated metrics.