SLIM: A finite-element, unstructured-mesh model forsimulating thermodynamic and dynamic sea-ice processes. : Application: the theory of the sea-ice age

In recent years, unstructured-mesh models have gained attention due to their flexibility in representing complex topography and variable spatial resolution. The Second generation Louvain-la-Neuve Ice-ocean Model (SLIM, www.climate.be/slim) is an unstructured-mesh finite element model that is being developed at the Université catholique de Louvain (Louvain-la-Neuve, Belgium). The ocean model solves the shallow water equations by means of the discontinuous Galerkin finite element method. It features a 1D river model, 2D depth averaged model and a full 3D model. After a general presentation of SLIM and its main applications, we will further focus on sea-ice modeling. The sea-ice component of SLIM has representations of both dynamic and thermodynamic sea-ice processes and includes viscous-plastic rheology along with a complete parametrization of the atmospheric fluxes. Unstructured meshes, with their natural ability to fit boundaries and increase locally the mesh resolution, propose an alternative framework to capture the complex oceanic areas formed by coasts and islands. Such an example is illustrated by the numerous narrow straits constituting the Canadian Arctic Archipelago. A key point of unstructured meshes is that they allow the use of mesh adaptivity. A Lagrangian, adaptive sea ice model allowing the computational grid to move with the ice drift is currently being developed. In order to maintain a good quality of the mesh, the mesh has to be adapted during the simulation, involving particular mesh adaptation techniques. This Lagrangian version of the model has several interesting applications, such as the dynamical mesh refinement along any region of interest (e.g., the ice edge), buoys tracking, or the inclusion of material properties in the rheology. Among these applications, the ice age constitutes both an interesting diagnostic tool and parameter for determining the ice physical properties (albedo, strength, salinity, ...). There are basically two ways of modeling the ice age: as a bidimensional tracer or as a vertical tracer, but different definitions exist and lead to different interpretations. In this work, we first present the equation of evolution of the age in an onedimensional ice layer. This equation is applied to a stand-alone thermodynamic sea ice model and its numerical resolution is compared to the integration of the ice age thanks to Lagrangian particles in the vertical direction. Preliminary results of a simulation of the Arctic Basin are finally shown where the Lagrangian model is used to transport the vertical structure of ice ag