Internal tide generation at a shelf break by an oblique barotropic tide: Observations and analytical modeling

An analytical model has been developed to describe the generation of a line ar interfacial wave over a steep ocean margin by a barotropic tide propagat ing toward the shelf break with a variable angle of incidence. The stratifi cation is reduced to a two-layer system, and the model uses step-like shelf geometry. In both shallow and deep regions an open boundary is assumed (th is implies particularly that there is no reflection at the coast). The mode l is forced with the amplitude and direction of an incident barotropic Poin care wave propagating toward the shelf break. With this forcing, the model gives the amplitude, direction of propagation, and wavenumber of both barot ropic and baroclinic Poincare waves transmitted onto the shelf and reflecte d into the deep region in the vicinity of the shelf break. After comparison with Baines' [1973] model, our model is compared with internal tide observ ations made in July 1996 on the Malin Shelf within the U.K. Land Ocean Inte raction Study-Shelf Edge Study program. The observations are from moored th ermistor chains and acoustic Doppler current profilers sited at two locatio ns, one near the shelf break and the other 47.5 km onto the shelf. Observat ions at this latter mooring are not described by the generation model becau se of nonlinear changes and damping as the internal wave propagates through shallow water. Baroclinic displacements of the thermocline of 8 m amplitud e were observed close to the shelf break, and total baroclinic energy was e stimated at 2.4 J/m(3) during neap tide and 3 J/m(3) during spring tide. Bo th amplitude and energy of the shoreward propagating internal tide waves ar e compared with the model. Using a barotropic forcing taken from bibliograp hical data, good agreement with observations is found during neap tide (whe n the density structure is close to being two-layer) for an incident barotr opic tide of 1 m amplitude and propagation direction on a bearing of 23 deg rees T (T means from True North in a clockwise sense).