NUMERICAL INVESTIGATIONS OF LINEAR INTERNAL TIDE GENERATION IN THE ROCKALL TROUGH

A fine resolution, linear, finite difference, 2-dimensional model has been used to study internal tide generation by solving for the streamfunction at a single frequency and using a simple parameterization of decay. A comparison with published laboratory data gave good agreement. Subsequently the model was run for the Malin Shelf edge, but this time comparison with field data was inconclusive. The results suggest that there is a critical region at the head of the slope which extends over a distance of about 10 km where the bottom depth changes from 200 to 700 m. Energy flows mainly up and down this slope onto the shelf and into the ocean, but in the upper ocean it also flows along the thermocline towards the shelf. The net flux is greater into the ocean than onto the shelf (≈ 100 against ≈20 W m-1). At the critical slope itself is a region of very low Richardson number which implies that significant mixing may be taking place. It is suggested that such mixing may play an important role in determining the form of internal tide energy radiating away from the shelf edge. The total flux is proportional to (σ2 - f2) 1 2, which changes slowly with σ in the semidiurnal frequency band. However, the solution at particular points in the model is more sensitive to changes in frequency. Horizontal shear in the north-flowing slope current probably modifies the effective frequency by up to 10% at the head of the slope. © 1990.