Abstract
Abstract. We describe FESOM-C, the coastal branch of the Finite-volumE Sea ice – Ocean Model (FESOM2), which shares with FESOM2 many numerical aspects, in particular its finite-volume cell-vertex discretization. Its dynamical core differs in the implementation of time stepping, the use of a terrain-following vertical coordinate, and the formulation for hybrid meshes composed of triangles and quads. The first two distinctions were critical for coding FESOM-C as an independent branch. The hybrid mesh capability improves numerical efficiency, since quadrilateral cells have fewer edges than triangular cells. They do not suffer from spurious inertial modes of the triangular cell-vertex discretization and need less dissipation. The hybrid mesh capability allows one to use quasi-quadrilateral unstructured meshes, with triangular cells included only to join quadrilateral patches of different resolution or instead of strongly deformed quadrilateral cells. The description of the model numerical part is complemented by test cases illustrating the model performance.
Highlights
Many practical problems in oceanography require regional focus on coastal dynamics
We described the numerical implementation of the threedimensional unstructured-mesh model FESOM-C, relying on FESOM2 and intended for coastal simulations
The model is based on a finite-volume cell-vertex discretization and works on hybrid unstructured meshes composed of triangles and quads
Summary
Many practical problems in oceanography require regional focus on coastal dynamics. global ocean circulation models formulated on unstructured meshes may in principle provide local refinement, such models are as a rule based on assumptions that are not necessarily valid in coastal areas. The limitations on dynamics coming from the need to resolve thin layers, maintain stability for sea surface elevations comparable to water layer thickness, or simulate the processes of wetting and drying make the numerical approaches traditionally used in coastal models different from those used in large-scale models. The code is based on the cell-vertex finite-volume discretization, the same as FESOM2 (Danilov et al, 2017) and FVCOM (Chen et al, 2003).
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