Simulating the Effects of Lower-Energy (<30 keV) Electrons on the Inner Magnetosphere Satellite Surface Charging Environment

Satellite surface charging often occurs in the inner magnetosphere from the pre-midnight to the dawn sector when electron fluxes of  hundreds of eV to tens of keV are largely enhanced. Inner magnetosphere ring current models can be used to simulate/predict the satellite surface charging environment, with their flux outer boundary conditions specified either based on observations or provided by other models, such as MHD models. In the latter approach, the flux spectrum at the outer boundary is usually assumed to follow a Kappa or Maxwellian distribution, which however often departs greatly from, or underestimates, the realistic distribution below tens of keV, the energy range that is crucial in the spacecraft surface charging anomaly. This study aims to optimize the electron flux boundary condition of the inner magnetosphere ring current model to achieve a better representation of the surface charging environment. The MHD-parameterized flux spectrum is combined with an empirical electron flux model that specifies the < 40 keV electron flux spectrum. New simulation results indicate that the surface charging environment, monitored by an integrated electron flux between 10<E<50 keV, is significantly enhanced by 1-2 orders of magnitude as opposed to the case in which Kappa/Maxwellian distribution is used at the outer boundary. The new results therefore show better agreement with Van Allen Probes measurements. The improved boundary condition also impacts the auroral precipitation, which may change the conductivity and circulated dynamics.