Long-term observations of mean winds and tides in the upper mesosphere and lower thermosphere above Scott Base, Antarctica

Analysis of monthly mean wind velocities from a medium frequency (MF) radar at Scott Base (78°S, 167°E), Antarctica, are presented. The radar has been measuring winds in the upper mesosphere and lower thermosphere region since December 1982. Previous work related to this instrument focused on only small portions of the larger dataset. The present study examines changes in the full dataset with respect to phenomena associated with multi-year periods, namely the quasi-biennial oscillation (QBO) and the solar cycle, and long-term trends. No relationship between these phenomena and the mean winds observed are identified. A negative correlation between the amplitude of the semi-diurnal tide and solar activity is found, similar to other mesosphere and lower thermosphere observations. This correlation is also observed for the diurnal tide to a lesser extent. Other observations have usually indicated negative trends in tidal amplitudes, however, a positive trend is found in tidal amplitudes at Scott Base since 1987. Processes that could lead to explanations for the observed seasonal variations, solar cycle dependence and the amplitude trend of the tides are discussed.