Impact of internal Tides on Boundary Conditions for Regional Models

The tides play an important role in the coastal ocean circulation. For most regional models, the barotropic tides are added via a boundary condition. Internal tides are generated by the interaction of the barotropic tides with bottom topography, typically leading to an offshore flux of baroclinic tidal energy. Recent theoretical studies have shown that onshore propagation of remotely generated internal tides can significantly change the circulation over the continental shelf. We study the impact of adding remotely generated internal tides to the regional boundary conditions using the output of a new global ocean circulation model which includes the astronomical gravitational forcing of the sun and moon to provide concurrent estimates of the barotropic and low vertical mode baroclinic tides. The traditional barotropic tidal boundary forcing can be replaced by the barotropic and baroclinic tide from the global ocean model with embedded tides. Three experiments are compared, traditional regional model with barotropic tidal boundary conditions, regional model with barotropic and baroclinic tidal boundary conditions from the global ocean model and the same shelf regional extracted from the global model for two different shelves, the NW Australia Shelf and the Oregon coast. Over most of the two shelves, the baroclinic flux is offshore with little impact from the baroclinic tidal boundary condition, but substantial differences occur due to the different resolution and bathymetry between the global and regional models.