Internal Tide Generation over Topography: Experiments with a Free-Surface z-Level Ocean Model

Abstract

A three-dimensional, z-level, primitive-equation ocean circulation model (DieCAST) is modified to include a free-surface and partial cells. The updating of free-surface elevation is implicit in time so that the extra computational cost is minimal compared with the original DieCAST code, which uses the rigid-lid approximation. The addition of partial cells allows the bottom cell of the model to have variable thickness, hence improving the ability to accurately represent topographic variations. The modified model is tested by solving a two-dimensional, linearized problem of internal tide generation over topography. Baines' method is modified to more cleanly separate the internal tide from the full solution. The model results compare favorably with the semianalytic solution of Craig. In particular, the model reproduces the predicted variation of internal tide energy flux as a function of the ratio of bottom slope to characteristic slope.