RADAR OBSERVATIONS OF THE SEMIDIURNAL TIDE IN THE MESOSPHERE AND LOWER THERMOSPHERE AT MIDLATITUDES

Observations of the atmospheric neutral winds in the altitude region b etween 80 and 130 km have been made at 43-degrees-N during the Lower T hermosphere Coupling Study campaigns, using the incoherent scatter rad ar at Millstone Hill and the meteor wind radar at Durham. The observat ions, covering three multi-day campaigns in September 1987, December 1 988 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 n umerical model predictions, and while there is general overall agreeme nt between the measurements and the model, the observations reveal a l arger variation amongst the data sets than predicted by the model. Suc h variation is also inherent in the mesospheric tidal winds observed b y other mesosphere lower thermosphere radars at middle latitudes, with which the Millstone Hill observations are compared.