TIDAL WINDS FROM THE MLT GLOBAL RADAR NETWORK DURING THE 1ST LTCS CAMPAIGN - SEPTEMBER 1987

Winds and tides were measured by a number of MLT (Mesosphere, Lower Thermosphere) radars with locations varying from 43-70°N, 35-68°S, during the first LTCS (Lower Thermosphere Coupling Study) Campaign, 21-25 September 1987. The mean winds were globally westerly, consistent with early winter-like (NH) and late winter (SH) circulations. The semi-diurnal tide had vertical wavelengths near or less than 100 km at most locations, with some latitudinal variation (longer/shorter at lower latitudes in the NH/SH)-amplitudes decreased at high latitudes. The global tide was closer to anti-symmetric, with northward components being in phase at 90 km. Numerical model calculations [Forbes and Vial (1989), J. atmos. lerr. Phys. 51, 649] for September have rather similar wavelengths and amplitudes; however, the global tide was closer to symmetric, and detailed latitudinal trends differed from observed. The diurnal tide had similar wavelengths in each hemisphere, with short values (~30 km) at 35°, long (evanescence) at 68-70°, and irregular phase structures at mid-latitudes. The tide was neither symmetric nor anti-symmetric. Model calculations for the equinox [Forbes. S and Hagan (1988), Planet. Space Sci. 36, 579] were by nature symmetric, and showed the short wavelengths extending to mid-latitudes (43-52°). Southern hemisphere phases were significantly (6-8 h) different from observations. Amplitudes decreased at high latitudes in model and observation profiles. © 1990.