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The EISCAT VHF radar (69.4°N, 19.1°E) has\udbeen used to record vertical winds at mesopause heights on a total of 31 days\udbetween June 1990 and January 1993. The data reveal a motion field dominated by\udquasi-monochromatic gravity waves with representative apparent periods of ~30–40\udmin, amplitudes of up to ~2.5 m s–1 and large vertical wavelength. In\udsome instances waves appear to be ducted. Vertical profiles of the\udvertical-velocity variance display a variety of forms, with little indication of\udsystematic wave growth with height. Daily mean variance profiles evaluated for\udconsecutive days of recording show that the general shape of the variance\udprofiles persists over several days. The mean variance evaluated over a 10 km\udheight range has values from 1.2 m2s–2 to 6.5 m2s–2\ud\udand suggests a semi-annual seasonal cycle with equinoctial minima and solsticial\udmaxima. The mean vertical wavenumber spectrum evaluated at heights up to 86 km\udhas a slope (spectral index) of –1.36 ± 0.2, consistent with observations at\udlower heights but disagreeing with the predictions of a number of saturation\udtheories advanced to explain gravity-wave spectra. The spectral slopes evaluated\udfor individual days have a range of values, and steeper slopes are observed in\udsummer than in winter. The spectra also appear to be generally steeper on days\udwith lower mean vertical-velocity variance. Key words. Meteorology and atmospheric dynamics (middle\udatmosphere dynamics; waves and tides)</p

Vertical velocities associated with gravity waves measured in the mesosphere and lower thermosphere with the EISCAT VHF radar