Absence of internal tidal beams due to non-uniform stratification

A linear internal-tide generation model is applied to the Faeroe-Shetland Channel, using observed profiles of stratification. Several degrees of simplification are considered: 1) uniform, i.e. constant N; 2) vertically varying N (z); 3) the full N(x, z) and associated geostrophic background flows. It is shown that clearly identifiable internal tidal beams and internal-wave attractors occur in the first case, but not in the other cases where the pattern is patchy due to internal reflections from the strong inhomogeneities in the medium. Given the general occurrence of pycnoclines and geostrophic background flows in the ocean, it is argued that this internal scattering can be expected to be a widespread phenomenon.