Radar observations of the semidiurnal tide in the mesosphere and lower thermosphere at midlatitudes

Observations of the atmospheric neutral winds in the altitude region between 80 and 130 km have been made at 43°N during the Lower Thermosphere Coupling Study campaigns, using the incoherent scatter radar at Millstone Hill and the meteor wind radar at Durham. The observations, covering three multi-day campaigns in September 1987, December 1988 and February 1990, have been used to deduce the characteristics of the semidiurnal tide, which show a general consistency with altitude as measured by the two techniques. Comparisons are made with current numerical model predictions, and while there is general overall agreement between the measurements and the model, the observations reveal a larger variation amongst the data sets than predicted by the model. Such variation is also inherent in the mesospheric tidal winds observed by other mesosphere-lower thermosphere radars at middle latitudes, with which the Millstone Hill observations are compared.