Wave-current interactions in the eastern Canadian waters

Abstract

This thesis examines effects of wave-current interactions (WCIs) on surface gravity waves and ocean currents over the eastern Canadian coastal and shelf waters using a coupled wave-circulation numerical model. The coupled model consists of a three-dimensional (3D) circulation model and a third-generation wave model. Comparisons of model results with in-situ oceanographic observations made with buoys and ADCPs and remote sensing measurements from satellites and high frequency (HF) radars demonstrate that the inclusion of WCIs in the coupled model significantly improves the model performance in simulating ocean waves, currents and hydrography over coastal and shelf waters, particularly during extreme weather events. The important WCI mechanisms on the 3D ocean currents examined in this study include the 3D wave force, breaking wave-induced mixing, and wave-induced vertical Reynolds stress. The research results demonstrate that the vortex force formulation, with a separation of the 3D wave force into conservative (vortex force and Bernoulli head) and non-conservative (breaking wave-induced acceleration) contributions, performs better than the radiation stress formulation in simulating the wave-induced 3D ocean currents over coastal waters under hurricane conditions. Furthermore, the 3D wave force and breaking wave-induced mixing are found to improve the model performance in simulating the storm-induced sea surface temperature changes. The research results also demonstrate that the wave-induced vertical Reynolds stress is an important process for transferring the wind momentum to the water column in addition to the turbulent Reynolds stress. The important WCI mechanisms on surface gravity waves during storm events include the relative wind effect, current-induced convergence and refraction, which collectively result in different wave responses on the two sides of the storm track. Significant wave modulations by the hurricane-induced near-inertial currents and semidiurnal tidal currents are also demonstrated based on analyses of both observations and numerical model results. Tidal modulations in the Gulf of Maine are mainly due to the strong horizontal gradients of tidal currents near the mouth of the Gulf, resulting in great effects of current-induced convergence, refraction and wavenumber shift. In addition, the current-enhanced dissipation becomes important during high winds by reducing the magnitude of the tidal modulation.