MEAN WINDS, TIDES AND GRAVITY-WAVES IN THE UPPER MIDDLE ATMOSPHERE DURING ALOHA-90

Wind measurements made with a partial reflection radar located on Christmas Island (2-degrees-N, 157-degrees-W) are used to describe the dynamical state of the equatorial mesopause region during ALOHA-90. Time mean westward (easterly) winds prevailed at most heights, and reached their maximum values of about -60 ms-1 near 85 km, but the mean meridional motions were weak. Strong oscillations due to the 24, 12, and 8 hr atmospheric tides were also observed in both wind components. The inferred vertical wavelengths were large, even for the diurnal tide. On the nights of 22 and 25 March, when airborne lidar observations were made in the vicinity of Christmas Island, the prevailing and tidal winds combined to produce especially strong westward winds (-100 ms-1). Gravity wave activity was also high during March/April, especially for short period waves, although considerable day-to-day variability was noted.