Abstract: Vertical wavenumber spectrum of vertical velocity fluctuations of atmosphere at heights of 70 - 100km is presented using vertical velocity data obtained from five chaff rocket measurements carried out during the MAC /SINE campaign in the summer of 1987 at Andenes, in Northern Norway (69°N, 16°E). The atmospheric vdrical wavenumber spectrum of the vertical velocity has a spectral gap at m=3.9×10^-4m^-1. At vertical wavenumbers greater than the spectral gap the vertical wavenumber spectrum agerees well with the saturated spectrum model. At vertieal wavenumbers smaller than the spectrla gap the vertical wavenumber spectrum has a slope of - 1.87 and a spectral amplitude that is an oder of magnitude lower than the saturated spectrum, suggesting that other geophysical processes besides gravity waves'may exist in the verticla velocity fluctuations.