Abstract: This paper utilizes horizontal velocity data with a high resolution of 25 m and temperature data with a low resolution of 1 km measured during the MAP/WINE and MAC/SINE campaigns to study seasonal variation of gravity wave spectrum near the polar mesopause. Direct measurement of the temperature allows accurate calculation of the spectral amplitude and Richardson number.Resultsshow that there is considerable variability in the slope and amplitude of the vertical wavenumber spectra of the horizontal velocity near the polar mesopause, which is not consistent with the predictions of various saturation models and the universal vertical wavenumber spectrum. However, the mean vertical wavenumber spectra reveal a significant seasonal variation:the mean spectrum in summer has saturated features, whereas the mean spectrum in winter has unsaturated features. This implies that the saturation processes are present in summer rather than in winter. Enhanced turbulence layer can therefore be expected to occur in summer compared to winter. This result is in rough agreement with the seasonal variation of turbulent energy dissipation rates. Richardson number Ri calculated from Brunt-Väisälä frequency N and horizontal wind shear S also reveals seasonal difference:dynamically unstable regions of Ri smaller than 1/4 are observed in summer, whereas stable regions of Ri larger than 0.4 are observed in winter. These unstable regions are found to associate well with the summer spectrum, whereas stable regions are found to associate well with the winter.