A comparison of atmospheric tides inferred from observations at the mesopause during ALOHA‐93 with the model predictions of the TIME‐GCM

Abstract

Observations made during the Airborne Lidar and Observations of Hawaiian Airglow (ALOHA‐93) campaign during October 1993 revealed the presence 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 compared with the predictions of the thermosphere/ionosphere/mesosphere electrodynamics general circulation model (TIME‐GCM). This model was recently tuned to agree with the observations from the Upper Atmosphere Research Satellite (UARS) with respect to mesosphere/lower thermosphere winds (60–200 km). It is found that although the TIME‐GCM agrees with UARS winds, it underpredicts the diurnal, and possibly the semidiurnal, tidal temperature perturbations seen during ALOHA‐93. Since the TIME‐GCM only includes migrating tides, this comparison suggests that nonmigrating tides may have had a significant amplitude during the ALOHA‐93 campaign period. UARS observations of the major nonmigrating diurnal mode were made just before and after the ALOHA‐93 period. It is found that the zonally symmetric nonmigrating tide can account for the discrepancy between the ALOHA‐93 results and the TIME‐GCM predictions only for a few periods and only at an altitude around 88 km. If the zonally symmetric nonmigrating tide is to account for the discrepancies between the model and the data, than it has to be highly variable.