A global ionospheric electrostatic potential model, which we refer to as Nopper-Carovillano (N-C), can be linked with a magnetospheric potential model. The latter model, which we refer to as Hill-Siscoe-Ober (H-S-O), computes a transpolar potential ΦPC(H-S-O) based on solar wind parameters and region-1 field-aligned currents (FAC) from the magnetosheath to the ionosphere. The polar ionospheric conductance required by H-S-O is defined by the N-C model. In this way, the transpolar potential and the associated FAC are the same in both models. A distribution of region-1 FAC in the N-C model predicts a two-cell convection pattern which is in reasonable agreement with plasma drifts measured by DMSP (Defense Meteorological Satellite Program) satellites. The H-S-O model, as modified by N-C, is compared with the Weimer potential model and with the transpolar potentials observed by DMSP satellites during the 6--7 April 2000 magnetic storm. Good agreement is found in both cases. The region-2 (J2) current is estimated from the Siscoe (S-RC) ring-current circuit model which is driven by ΦPC(H-S-O). The resistor values in S-RC, as determined by N-C, when combined with the global potential solution, make it possible to estimate the time profile of the equatorial penetration electric field during the storm's main phase. With the values obtained, shielding occurs within 1 hour of onset. Equatorial plasma bubbles (EPBs) are seen some hours after the initial increase of ΦPC and are qualitatively consistent with the equatorial penetration electric field calculated by the combined model.