Mesospheric winds at low‐ and mid‐latitudes in the southern hemisphere

Abstract

Mesospheric wind measurements were made by using the partial reflection technique at a tropical location (Townsville, 19°S), and at a mid‐latitude location (Adelaide, 35°S) in June and November 1978. It is shown that the prevailing winds were typical of expected winter and summer type circulations in June and November, respectively, but there was a large difference in the amplitudes and structure of the diurnal tide between the two sets of observations. In November the tide was stable with a large amplitude and it appeared to ‘break’ at a height of 86 km. The propagating S 1,1 , mode dominated. In June, however, the tide was weak with large day‐to‐day variability and the evanescent S 1,−2 mode was dominant. The semi‐diurnal tide amplitudes were relatively small but internal gravity wave amplitudes were significant. Spectral analyses showed that in the 2 to 8 hour period band the wave energy decreased as f −k with k in the range 1–1.5 and it is also shown that the waves were losing energy as a function of height. The inferred energy loss rates were ∼0.05 W kg −1 and a turbulent viscosity of about 500 m² s −1 was estimated near the mesopause at both sites and in both seasons.