Hydrostatic and non-hydrostatic studies of gravitational adjustment over a slope

In many numerical ocean models, the hydrostatic approximation is made. This approximation causes a considerable saving in computing time. However, for phenomena involving large vertical speeds, for many small scale phenomena, and in areas with weak stratification, the approximation becomes questionable. In this report, a σ -coordinate hydrostatic C-grid model is extended to include non-hydrostatic dynamics. The test cases involve gravitational adjustment of a downslope flow. The first test case has a simplified slope profile and no ambient stratification in the deep basin. The second test case has ambient stratification and more realistic topography. The differences between hydrostatic and non-hydrostatic simulations are described and discussed. It is shown that the shapes of the head and the body of density driven plumes are better preserved in the non-hydrostatic experiments. The wave propagation away from the plume head is considerably reduced when including non-hydrostatic effects.