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

Thirty-three foil chaff rockets were flown at high latitudes during the sum mers of 1987, 1988, and 1991. Vertical profiles of horizontal wind were obt ained at high resolution (25 m) in the 67-103 km region of the mesosphere a nd lower thermosphere. This resolution (at that range of attitude) is uniqu e and provides sensitivity to more than two decades of vertical wavenumbers . This study utilizes the unique data set to present observed spectra and t heir mean characteristics. Average vertical wavenumber spectra indicate tha t there is excellent agreement with the saturated gravity wave spectral mod el developed by Dewan and Good (J. Geophys. Res. 91(D3) (1986) 2742) and Sm ith 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 the ory in a mean sense and suggests that saturation processes are present in t he horizontal flow and act to produce turbulence. We can therefore expect t hat turbulence is enhanced near the polar summer mesopause. Dominant vertic al wavelength obtained from the average spectra is estimated to be 12.8 km. (C) 2001 Elsevier Science Ltd. All rights reserved.