Ocean modeling on unstructured meshes

4 Unstructured meshes are common in coastal modeling, but still rarely used 5 for modeling the large-scale ocean circulation. Existing and new projects 6 aim at changing this situation by proposing models enabling a regional 7 focus (multiresolution) in global setups, without nesting and open bound8 aries. Among them, finite-volume models using the C-grid discretization on 9 Voronoi-centroidal meshes or cell-vertex quasi-B-grid discretization on trian10 gular meshes work well and offer the multiresolution functionality at a price 11 of being 2 to 4 times slower per degree of freedom than structured-mesh 12 models. This is already sufficient for many practical tasks and will be fur13 ther improved as the number of vertical layers is increased. Approaches based 14 on the finite-element method, both used or proposed, are as a rule slower at 15 present. Most of staggered discretizations on triangular or Voronoi meshes al16 low spurious modes which are difficult to filter on unstructured meshes. The 17 ongoing research seeks how to handle them and explores new approaches 18 where such modes are absent. Issues of numerical efficiency and accurate 19 transport schemes are still important, and the question on parameterizations 20 for multiresolution meshes is hardly explored at all. The review summarizes 21 recent developments the main practical result of which is the emergence of 22 multiresolution models for simulating large-scale ocean circulation. 23