G. Kivman

A finite-element ocean model: principles and evaluation

Abstract We describe a three-dimensional (3D) finite-element ocean model designed for investigating the large-scale ocean circulation on time scales from years to decades. The model solves the primitive equations in the dynamical part and the advection–diffusion equations for temperature and salinity in the thermodynamical part. The time-stepping is implicit. The 3D mesh is composed of tetrahedra and has a variable resolution. It is based on an unstructured 2D surface mesh and is stratified in the vertical direction. The model uses linear functions for horizontal velocity and tracers on tetrahedra, and for surface elevation on surface triangles. The vertical velocity field is elementwise constant. An important ingredient of the model is the Galerkin least-squares stabilization used to minimize effects of unresolved boundary layers and make the matrices to be inverted in time-stepping better conditioned. The model performance was tested in a 16-year simulation of the North Atlantic using a mesh covering the area between 7° and 80° N and providing variable horizontal resolution from 0.3° to 1.5°.

Improved Estimates of the Oceanic Circulation Using the CHAMP Geoid

Ocean general circulation models which are constrained by altimetry data usually assimilate only temporal sea-surface height anomalies. It is known that this is not enough to correct the mean ocean state. Here we present first results of assimilating the full (absolute) dynamical topography into a steady state version of a finite element ocean model (FEOM) for the North Atlantic. This makes it possible to notably reduce the model-data misfit especially in the western part of the basin and in the southern Labrador Sea.