Satellite surface charging often occurs in the inner magnetosphere from the pre-midnight to the dawn sector when electron fluxes of tens of keV are largely enhanced. Inner magnetosphere ring current models can be used to simulate/predict the satellite surface charging environment, with their 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 function parameterized from MHD quantities, which however often departs greatly from, or underestimates, the realistic distribution for E< tens of keV, the crucial energy range in the spacecraft surface charging anomaly. This study aims to optimize the setting of the electron flux boundary condition of the inner magnetosphere ring current model, in order to achieve a better representation of the surface charging environment. Therefore, we propose to combine the MHD-parameterized flux spectrum with an empirical electron flux model of E<40 keV at the boundary. Simulation results with the new boundary condition 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, leading to a much better agreement with Van Allen Probes measurements, as opposed to the case in which the MHD-parameterized Kappa/Maxwellian distribution is solely used at the outer boundary. This study hence provides a reasonable solution to the outer boundary setting and should be taken into account in geospace circulation models.

内磁层,卫星表面充电