A recent development of the coupled thermosphere-ionosphere-plasmasphere model (CTIP) has been the inclusion of the electrodynamic coupling between the equatorial ionosphere and thermosphere. The vertical ion drifts which result are shown to be largely in agreement with empirical data, on the basis of measurements made at the Jicamarca radar and other equatorial sites [Scherliess and Fejer, 1999>. Of particular importance, the CTIP model clearly reproduces the prereversal enhancement in vertical ion drift, a key feature of the observational data. Inacurracies in the modeled daytime upward ion motion have been investigated with regard to changing the magnitude and phase of components of the lower thermospheric tidal forcing. The results show that daytime vertical ion motion is highly dependent upon both the magnitude and phase of the semidiurnal tidal component. In addition, the CTIP model shows the prereversal enhancement to be unaffected by changes in tidal forcing, but only for conditions of high solar activity. During periods of low solar activity the form of the prereversal enhancement is clearly dependent upon the magnitude and phase of the semidiurnal tide. ¿ 2001 American Geophysical Union