| Résumé en anglais |
The tridimensional SPEM numerical model based on primitive equations, initially developed by Haidvogel et al. (1991) is used to explore the effects of an isolated seamount on a simple oceanic flow. The flow configuration chosen is that of a simple rectangular canal in which a uniform current flows and the middle of which contains an axisymmetrical submerged obstacle. The canal has two open boundaries. At these boundaries, specific numerical boundary conditions have been developed to permit long-term numerical integrations. Various situations were explored according to the different parameters of the problem, essentially the Rossby number, the intensity of stratification and the amplitude of the topography. The objective is to indicate the steady and unsteady characteristics of eddy perturbations generated at mesoscales by a flow over an isolated topography. Where the homogeneous situation in conditions close to quasi-geostrophy is concerned, the effect of stratification is to confine in depth the anticyclonic structure created by the topography. For finite Rossby numbers, a cyclonic eddy structure is also present, coupled with the previous anticyclonic one. As regards transient phenomenon such as circular trapped waves, the effect of ageostrophy is less clear. Even for large topographic amplitude, flow properties are recovered that are typical of the quasi-geostrophic approximation. Lastly, the influence of controlling parameters on the generation and geometry of Taylor caps is identified. The increase of stratification appears to be a very sensitive factor in limiting the vertical extent of Taylor caps. |
