The influence of topographic features and density variations upon the internal tides in shelf edge regions
A brief outline of the development of a three-dimensional primitive equation baroclinic model for computing the internal tides is presented. A series of calculations are performed to examine the internal tide in the shelf edge region off the west coast of Scotland, with the aim of determining the influence upon the internal tide in the region of topographic features, namely large-scale features, such as seamounts, and small-scale features, such as a detailed specification of the shelf slope, which is possible using results from a recent survey rather than topographic data taken from a coarse grid model using depths interpolated from charts. The influence upon the solution of small variations in the density field and seasonal variations is examined. Also, the influence of a well-mixed bottom boundary layer at the base of the shelf slope, produced possibly by cascading of dense water off the shelf during a major wind event, upon the internal tide is also examined. In the calculations described here the model is used in cross-shelf form. A comparison of internal tides computed with and without the inclusion of an offshore seamount shows that internal tides are produced along the sides of the seamount, and can propagate towards the shelf edge, and thereby influence the internal tidal signal in that region. A comparison of internal tides computed using previously available bottom topography extracted from charts with those computed using a detailed topographic data set from a recent survey shows the importance of accurate topography in the shelf edge region for internal tide calculations. Simulations show that the internal tide is influenced by variations in the density field, suggesting that an accurately measured density field is essential for internal tide determination. Calculations also show that if a well-mixed sea bed boundary layer occurs at the bottom of the shelf slope, the internal tide can be reflected by this feature giving rise to significant internal tides in the ocean at larger distances from the shelf edge than in the absence of this water mass. Copyright (C) 1999 John Wiley & Sons, Ltd.
internal tides shelf edge seamount cascading topography numerical model