Variability in the Coastal Response of the Baroclinic Basin Mode Generated by Direct Forcing from the Barotropic Tide Generating Potential in an Idealized Ocean Basin

Current variability on many continental shelves is dominated by internal tides. Observations show along-coast variability in internal tide energy, structure, and propagation, but the nature of this variability is not known. Here, we use the Regional Ocean Modeling System (ROMS) to test our hypothesis that direct forcing of internal tide basin modes by the tide generating potential can generate large amplitude internal tides on continental margins, dependent on parameters such as shelf and slope structure, stratification, and Coriolis parameter. The domain is an idealized, stratified, mid-latitude rotating ocean basin with horizontally uniform continental shelf and slope around the deep basin, with horizontally uniform stratification, forced by the equilibrium M2 barotropic tide. Two stratifications are compared: one that has an internal tide wavelength over the shelf that is four times the shelf width and one that is twice the shelf width. The results show that the coastal response to the baroclinic basin mode is dependent on the relationship between stratification and shelf structure. We determine how large-scale (along-coast length scales greater than the internal tide wavelength) variations in continental shelf/slope geometry control alongshelf internal tide response via coupling to internal tide modes. We propose that some of the intermittency in along-coast internal tides is due to variability in the basin-mode response from temporal changes in stratification.