Sack Lunch Seminar (SLS)

As is well known, tides in a stratified system include a baroclinic, or internal, mode characterized by relatively short horizontal scales and large interfacial displacements at depth. We show here that the introduction of stratification into global numerical tide models changes the large-horizontal scale, or barotropic, tide as well, typically by about 1-5%. Motivated by the impact of stratification on the barotropic tide, we then show that perturbations to the oceanic stratification yield further changes in both the barotropic and baroclinic components of surface tidal elevations. An analytical model of tides in a two-layer system also shows that stratification and perturbations to stratification impact the barotropic as well as baroclinic tides. Taken together, the numerical and analytical results therefore suggest that climatic perturbations to oceanic stratification may contribute to the secular changes in tides seen in tide gauge observations taken over the last century or so.