We used the National Center for Atmospheric Research thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) to calculate the variability of the migrating diurnal tide in a January through December 1993 simulation. While TIME-GCM captures the salient features of the latitudinal, altitudinal, and seasonal variability of the migrating diurnal tide, upper mesospheric meridional wind amplitudes are somewhat smaller than those that have been observed from the ground and space. The discrepancies may be attributable to unresolved uncertainties in tidal forcing and/or dissipation in the TIME-GCM. However, our diagnostic simulation suggests that the nonlinear interactions between the migrating diurnal tide and stationary planetary wave 1 produce measurable nonmigrating diurnal tidal components that modulate migrating diurnal tidal amplitudes and account for significant variability in the upper mesosphere and lower thermosphere. ¿ 2001 American Geophysical Union