Direct comparisons of prevailing winds and tidal wind fields (24-, 12-h) in the upper middle atmosphere (60–105 km) during 1978–1980 at Saskatoon (52°N, 107°W) and Christchurch (44°S, 173°E

Abstract

Continuous observations of the upper Middle Atmosphere (60–110 km) have been made since 1978 by M. F. radars at Saskatoon, Canada (52°N, 107°W) and Christchurch, New Zealand (44°S, 173°E). There are important differences in the zonal mean winds between hemispheres and, hence, with CIRA (1972), e.g. summer westward and winter eastward reversal heights. Other differences with CIRA involve the considerable winter variability at each location and the rapidity of the equinoctial transitions. The semi-diurnal tide shows similar strong seasonal variations in amplitudes, phases and wavelengths at each location, e.g. there are generally shorter wavelengths in fall-winter months (~45 km) than in spring-summer (≳100 km). Also, for most months the northward tidal components are closer to being in phase than the eastward near 90 km, favouring the dominance of antisymmetric modes. Recent theoretical models do not match these features well. The weaker diurnal tide also shows marked seasonal variations. Comparisons are also made with tidal and mean wind data from Adelaide (35°S) and Kyoto (35°N) for the same observing interval: there is frequently useful agreement between the four locations.