A parametric study of magnetosphere-ionosphere coupling in the paleomagnetosphere

Geomagnetic polarity reversals last about 1-8 thousand years, while the intensity of the Earth's dipole field may drop as much as 1 order of magnitude. In this paper, we aim at modeling the paleomagnetosphere, in particular, the magnetosphere-ionosphere coupling during such polarity transition epochs, using the BATS-R-US global magnetohydrodynamic (MHD) simulation code. We study the variation of the transpolar potential and the total field aligned currents with changing dipole moment, ionospheric Pedersen conductance, and interplanetary magnetic field. The simulations remarkably well reproduce the transpolar potential saturation predicted by the analytical Hill model and confirmed by observations. Estimates of transpolar potential and region 1 field aligned currents are given for paleomagnetospheres with strongly decreased dipole moments. In general, a fairly good agreement was found between the simulation results and the predictions of the Hill model, however, MHD simulations give a somewhat steeper drop of transpolar potential as the dipole moment decreases. Some corrections to the dipole scaling relation in the Hill model are suggested.