Tidal Winds from the Mesosphere, Lower Thermosphere Global Radar Network during the second LTCS Campaign: December 1988

Abstract

Winds and tides were measured by nine MLT (mesosphere, lower thermosphere) radars with locations between 70°N and 78°S, including an equatorial station at Christmas Island, 2°N (Avery et al., 1990). The mean winds were eastward (westward) in the northern (southern) hemisphere mesosphere, consistent with midwinter circulations. For the 12‐hour (semidiurnal) tide, observations and the model of Forbes and Vial (1989) were in generally good agreement: in both cases northward components were closer to being in phase in the two hemispheres, and winter wavelengths were shorter than those of the mid‐latitude summer. Major differences were large (small) amplitudes at 70°N for model (observations); and poor agreement of equatorial tidal profiles. For the 24‐hour (diurnal tide), the radar observations and model of Forbes and Hagan (1988) were in useful agreement in the summer hemisphere. However, the short (long) wavelengths at mid (high) latitudes of the model's winter hemisphere were not observed during LTCS (Lower Thermosphere Coupling Study) 2, nor in climatologies for December. Suggestions as to the reasons for this disparity are presented.