MEAN WINDS AND TIDES IN THE UPPER MIDDLE ATMOSPHERE AT URBANA (40-DEGREES-N, 88-DEGREES-W) DURING 1991-1992

A summary of the first 18 months of continuous wind observations using the Urbana medium frequency (MF) radar is presented. Emphasis is placed on height-time contours of monthly mean winds and on amplitudes and phases of 24 hour and 12 hour tides. Results are compared with data from other midlatitude stations and models. Below 85 km, monthly mean winds are shown to agree closely with the zonal mean, geostrophic wind model CIRA86. Significant discrepancies above 85 km have been noted in comparisons between CIRA86 and the other mesosphere-lower-thermosphere (MLT) radar stations (including MF, meteor, and low-frequency (LF) radars) and are also sustained in the observations reported here. Tidal characteristics are generally consistent with other midlatitude observations, although significant differences are noted between Urbana and its closest MLT network neighbor station (Durham, 43-degrees-N, 71-degrees-W). The mean wind observations provide a context for the gravity wave climatology derived from Na lidar observations at Urbana and promise to contribute toward improvements of middle atmosphere wind and tidal models.