Internal Gravity Waves in the Mesosphere and Lower Thermosphere at Mid-Latitudes

Abstract

Wind data from approximately 75–110 km for the years 1972–75 have been obtained by the radiowave partial reflection drift technique. A summary of data which have appeared in earlier papers, and which relate to internal gravity (IG) waves, is given; and some of these data are subjected to additional analysis. Several of the new results reinforce the earlier interpretation, which involves coupling between IG waves and the mean flow. Associations are also found between IG wave amplitudes and the heights of reversals of the westward mean winds during autumn months of 1974; similar associations have been found previously for spring mouths. A related comparison between the magnitudes of the zonal and meridional components of the IG waves suggests important seasonal variations in the phase velocities of waves incident upon the mesosphere. Spectral analysis techniques are used to show the coherence of IG wave modes (20≲τ≲120 min) within the mesosphere and thermosphere.