Observational evidence indicates that high-latitude magnetic activity can be causally related to fluctuations and reversals of the equatorial electric field. Using Birkeland currents as the driving forces, we have made numerical calculations of the ionospheric electric fields and currents that distribute globally. Our calculations utilize a fairly realistic empirical ionospheric conductivity model and the field-aligned current distribution inferred from TRIAD measurements. The results presented here demonstrate that the field-aligned currents observed during disturbed periods can account for the equatorial fluctuations and reversals in electric field and associated magnetic disturbances noted during such times. In this way, magnetospheric dynamics has a direct and significant influence on the equatorial ionosphere through the ionospheric conductivity.