Spectral Estimates of Gravity Wave Energy and Momentum Fluxes. Part III: Gravity Wave-Tidal Interactions

Abstract

An application of the gravity wave parameterization scheme developed in the companion papers by Fritts and VanZandt and Fritts and Lu to the mutual interaction of gravity waves and tidal motions is presented. The results suggest that interaction is likely to be strong where tidal amplitudes become large, yielding a significant modulation in the anisotropy of the gravity wave field due to differential filtering and saturation processes. Consistent with observations, this filtering leads to wave momentum fluxes that are approximately anticorrelated with the tidal wind field and may far exceed mean values in magnitude. A simple analytic model of the tidal motion and the induced gravity wave momentum fluxes suggests that the flux divergence contributes substantial accelerations of the local mean motion, yielding both an advance in time (or descent) of the tidal phase and apparent tidal amplitude variations that depend on tidal structure.