Mesospheric Momentum Fluxes Observed by the MST Radar at Poker Flat, Alaska

Abstract

An analysis of the wave motions observed with the Poker Flat MST radar during the winter, summer, and fall of 1986 is presented in this paper. Monthly and daily mean winds, momentum fluxes, and velocity variances are investigated in detail. While several features are in agreement with previous measurements, some significant differences also are found to exist in our observations. Monthly mean horizontal winds between 82 and 89 km have amplitudes of ?20?40 m s?1 westward and ?10?25 m s?1 southward in July and August. In fall and winter, the horizontal winds between 58 and 75 km are weaker and essentially eastward. Monthly mean vertical velocities are predominantly downward at ?0.3 m s?1, which implies a vertical wave energy flux of ?0.1 W m?2, higher than that estimated at low latitudes. Monthly mean horizontal variances are ?1600 m2 s?2 in summer, and 600 m2 S?2 in fall and winter with vertical variances ?3 m2 s?2. Monthly mean zonal and meridional momentum fluxes, contributed predominantly by waves of periods less than 1 hour, are of the order of 6?10 and 4 m2 s?2 in summer, and ??1 to ?2 and +0.1 m2 s?2 in fall and winter. These momentum fluxes are significantly larger than those observed at lower latitudes, but are comparable with other measurements at high latitudes. Also observed is large daily variability of the velocities, momentum fluxes, and variances, suggestive of a highly active and variable wave environment and a strong influence of gravity waves on the mean mesospheric structures at high latitudes.