A study of the interactions of tides and gravity waves

The seasonal variability of tidal amplitudes in the mesosphere is thought to be the result of the interaction of tides and gravity waves. This hypothesis will be explored through the use of a gravity wave parameterization developed by Alexander and Dunkerton and a linear steady state tidal model. We will examine in detail how the tide/gravity wave interaction depends on the structure of the background winds, the structure of the tidal wind profile and the structure of the gravity wave spectrum. Following Miyahara and Forbes, we will represent the wave drag and diffusion in terms of a complex effective friction coefficient. A complex coefficient represents not only the amplitude of the damping due to gravity waves but also the phase of its temporal variability with respect to the tidal oscillation. The effect of the wave drag on the modal structure of the tides will be explored with the tidal model.