Mean characteristics of the spectrum of horizontal velocity in the polar summer mesosphere and lower thermosphere observed by foil chaff

Abstract Thirty-three foil chaff rockets were flown at high latitudes during the summers of 1987, 1988, and 1991.Vertical profiles of horizontal wind were obtained at high resolution (25 m ) in the 67– 103 km region of the mesosphere and lower thermosphere. This resolution (at that range of altitude) is unique and provides sensitivity to more than two decades of vertical wavenumbers. This study utilizes the unique data set to present observed spectra and their mean characteristics. Average vertical wavenumber spectra indicate that there is excellent agreement with the saturated gravity wave spectral model developed by Dewan and Good (J. Geophys. Res. 91(D3) (1986) 2742) and Smith et al. (J. Atmos. Sci. 44(10) (1987) 1404), which has a slope of −3 and a spectral amplitude proportional to the buoyancy frequency squared. This excellent agreement provides further support for the saturated spectrum theory in a mean sense and suggests that saturation processes are present in the horizontal flow and act to produce turbulence. We can therefore expect that turbulence is enhanced near the polar summer mesopause. Dominant vertical wavelength obtained from the average spectra is estimated to be 12.8 km .