The National Center for Atmospheric Research thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) is used to study the local time variation of the equatorial O(1S) emission rate observed by the wind imaging interferometer (WINDII) instrument on the Upper Atmosphere Research Satellite for equinox conditions during 1992 and 1993 [Shepherd et al., 1995>. In the evening the airglow emission layer is very bright and descends with time. At about midnight the emission rate is drastically reduced, with a deep midnight minimum. Shortly afterward, the emission rate begins to recover at higher altitudes and increases toward dawn. The TIME-GCM simulations show that if the diurnal tide has sufficient amplitude to penetrate the atomic oxygen layer near 97 km, then it significantly alters the atomic oxygen distribution at low latitudes, producing a strong green line variation similar to the WINDII observations. At latitudes greater than 20 ¿N and 20 ¿S latitude the opposite variation occurs, indicating a global oscillation in the atomic oxygen layer. If the diurnal tide is weak, it does not penetrate the layer and there is only a weak semidiurnal variation of the nighttime green line similar to what is generally observed for solstice conditions.¿ 1997 American Geophysical Union