The role of magnetic flux tube deformation and magnetosheath plasma beta in the saturation of the Region 1 field-aligned current system

The phenomena of cross polar cap potential (CPCP) and ionospheric field-aligned current (FAC) saturation remain largely unexplained. In the present study, we expand upon the Alfvén wing model of CPCP saturation by investigating its impact on the magnetosphere-ionosphere current system, particularly the Region 1 FAC input into the polar cap. Our hypothesis is that the ability of open flux tubes to deform in response to applied fluid stress from the magnetosheath is governed by the magnetosheath plasma beta, which in turn governs the Maxwell stress imposed on ionospheric plasma from the magnetosphere. We performed 32 MHD simulations with varying solar wind density and interplanetary magnetic field strength and show that the plasma beta does govern the deformation of open field lines, as well as the nonlinear response of the Region 1 FAC system to increasingly southward interplanetary magnetic field. Further, we show that the current-voltage relationship in the ionosphere also shows a dependence on the plasma beta in the magnetosheath, with the ionosphere becoming more resistive at lower beta.