Modelling of field-aligned currents in the dayside polar oval

Mathematical models of a fully closed magnetospheric magnetic field and of a diffusive magnetopause are combined to calculate the electric field and the field-aligned currents in the dayside cusp region of the ionosphere. The electric potential at the magnetopause resulting from magnetic field diffusion is mapped into the ionosphere and then used to calculate the field-aligned currents in the ionosphere. The obtained field-aligned current system includes region 1 located along the equatorial boundary of the cusp, and region 3 located by 1-2 degrees poleward. The region 1 in the model corresponds to the frontside of the magnetospheric boundary whereas the region 3 is coupled with the magnetopause in the magnetotail. Region 3 currents are shown to be due to the electric potential magnitude decreasing in the antisolar direction. Such a behaviour of the electric potential looks natural for all other possible electric held generation mechanisms at the magnetopause and, therefore, it is reasonable to expect them to generate region 3 field aligned currents.