A COMPARISON OF ATMOSPHERIC TIDES INFERRED FROM OBSERVATIONS AT THE MESOPAUSE DURING ALOHA-93 WITH THE MODEL PREDICTIONS OF THE TIME-GCM

Observations made during the Airborne Lidar and Observations of Hawaii an Airglow (ALOHA-93) campaign during October 1993 revealed the presen ce of persistent large perturbations of the temperature and density in the 80 to 100 km mesopause region. These perturbations, seen both by passive airglow and active lidar techniques, were identified as due to the presence of diurnal and semidiurnal tides. These results were com pared with the predictions of the thermosphere/ionosphere/mesosphere e lectrodynamics general circulation model (TIME-GCM). This model was re cently tuned to agree with the observations from the Upper Atmosphere Research Satellite (UARS) with respect to mesosphere/lower thermospher e winds (60-200 km). It is found that although the TIME-GCM agrees wit h UARS winds, it underpredicts the diurnal, and possibly the semidiurn al, tidal temperature perturbations seen during ALOHA-93. Since the TI ME-GCM only includes migrating tides, this comparison suggests that no nmigrating tides may have had a significant amplitude during the ALOHA -93 campaign period. UARS observations of the major nonmigrating diurn al mode were made just before and after the ALOHA-93 period. It is fou nd that the zonally symmetric nonmigrating tide can account for the di screpancy between the ALOHA-93 results and the TIME-GCM predictions on ly for a few periods and only at an altitude around 88 ken. If the zon ally symmetric nonmigrating tide is to account for the discrepancies b etween the model and the data, than it has to be highly variable.