On The Scattering Of Topographically Modified Semidiurnal Kelvin Waves Into Internal Waves

Semidiurnal tides propagate along continental shelves as a Kelvin wave mode. On wide continental shelves, the shelf topography modifies the Kelvin wave mode into a hybrid Kelvin-edge wave (HKEW), with features of a zero mode edge wave. Its free surface structure and alongshore energy flux concentrate on the shelf, and are sensitive to changes in the shelf width. When a propagating HKEW encounters an alongshore change of shelf width, the adjustment of wave structures results in the scattering of the incident wave into other wave modes, including barotropic and baroclinic Poincaré waves radiating offshore. These dynamics are studied using the Regional Ocean Modeling System (ROMS) under barotropic and stratified conditions. The model consists of two alongshore-uniform continental shelves of different widths adjoined through a transition zone. The continental shelf and slope are adjacent to an ocean of a constant depth. The barotropic model shows that when the shelf width changes, the barotropic alongshore energy fluxes diverge on the shelf. This divergence of alongshore energy fluxes leads to a cross-isobath energy flux. The stratified model shows that when the cross-isobath energy flux is offshore, the incident energy scatters into barotropic wave modes. When the energy flux is onshore, more than 10% of the incident energy can scatter into internal wave modes under favorable conditions. This internal tide generation mechanism is relevant to the coastal ocean with strong semidiurnal tides and wide continental shelves, such as the Celtic Sea and the Patagonian Shelf. Analysis of observational data reveals strong internal tide signals near the Patagonian shelf break. Proxy vectors of the baroclinic energy fluxes show that the internal tide propagation occurs predominantly along the isobaths and is not aligned with the barotropic tide, possibly due the internal wave refraction on the Malvinas Current