GRAVITY-WAVE MOTIONS IN THE MESOSPHERE AND LOWER THERMOSPHERE OBSERVED AT MAWSON, ANTARCTICA

We present the results of MF radar observations of mean winds and wave s in the height range 78-108 km at Mawson (67-degrees-S, 63-degrees-E) , Antarctica. The measurements were made in the period from 1984 to 19 90. Climatologies of the prevailing zonal and meridional circulations made with a 12-day time resolution show that the mean circulation rema ined relatively stable over the 6 yr of observation. Climatologies of gravity-wave motions in the 1-24 h period range were also generated. T hese reveal that the r.m.s. amplitudes of horizontal wave motions near the mesopause (approximately 90 km) are about 30 m s-1, and that ther e is some anisotropy in the motions, especially at heights below 90 km . Meridional amplitudes are larger than zonal amplitudes, which sugges ts a preference for wave propagation in the north-south direction. Com parisons with MST radar wind observations made near the summer solstic e at Poker Flat, Alaska (65-degrees-N) and at Andoya, Norway (69-degre es-N) show similarities with the Mawson observations, but the wave amp litudes and mean motions are larger in magnitude at the northern sites . This suggests hemispheric differences in wave activity that require further study.