Internal tide generation in semi-enclosed ocean basins

Abstract When they interact with topography in the presence of stratification, astronomically driven barotropic tides lose part of their energy to internal tides. Many numerical and observational studies on internal tide generation have been focused on either generation at ocean ridges and isolated topographical features or generation at the open coast, but not in semi-enclosed basins. Because of their long wavelengths, potentially comparable to horizontal basin scales, internal tides may be resonant with natural basin modes, which could explain previous observations of large amplitude internal tides in some basins. Yet, what is an appropriate basin geometry to elicit a resonant response is poorly understood. Vertical stratification and its interaction with coastal bathymetry are likely to have a significant impact on the generation and dynamics of internal waves. Here, we conduct a series of idealized 3D numerical simulations of semi-enclosed, continuously vertically stratified rotating basins with shelf bathymetry along the perimeter of the basin. We force these basins with a periodic barotropic coastal Kelvin wave to investigate under what physical characteristics of a basin are resonant baroclinic modes generated. Through our parameter sweep, we identify relevant nondimensional parameters that can be used to find characteristics of a basin resonant to a particular frequency. An important result from this study is that, in the presence of basin shelf bathymetry, coupling between basin modes and coastal trapped waves strongly modifies the dynamics of the resonant response.