The relative importance of geoeffective length versus Alfvén wing formation in the saturation of the ionospheric reverse convection potential

We compare the relative importance of two competing mechanisms (Alfven wing vs. magnetosheath force balance) in determining the saturation of the reverse convection potential under northward interplanetary magnetic field. We run the Lyon-Fedder-Mobarry magnetohydrodynamic model under strong northward interplanetary magnetic field (20 nT) twice: once with a solar wind number density of 20 cm(-3) and once with a density of 2 cm(-3). We find that the reverse convection potential is reduced for the low-density run, as predicted by both models. We also find that despite the formation of Alfven wings, the sunward flows in the magnetosphere are governed by the local reconnection physics. Further, the length of the x-line poleward of the cusp is reduced by a factor of 2 for the low-density run. This suggests that the reverse convection potential is governed by the local reconnection physics at the x-line and the geoeffective length.