Abstract
Abstract. Version 2 of the unstructured-mesh Finite-Element Sea ice–Ocean circulation Model (FESOM) is presented. It builds upon FESOM1.4 (Wang et al., 2014) but differs by its dynamical core (finite volumes instead of finite elements), and is formulated using the arbitrary Lagrangian Eulerian (ALE) vertical coordinate, which increases model flexibility. The model inherits the framework and sea ice model from the previous version, which minimizes the efforts needed from a user to switch from one version to the other. The ocean states simulated with FESOM1.4 and FESOM2.0 driven by CORE-II forcing are compared on a mesh used for the CORE-II intercomparison project. Additionally, the performance on an eddy-permitting mesh with uniform resolution is discussed. The new version improves the numerical efficiency of FESOM in terms of CPU time by at least 3 times while retaining its fidelity in simulating sea ice and the ocean. From this it is argued that FESOM2.0 provides a major step forward in establishing unstructured-mesh models as valuable tools in climate research.
Highlights
Ocean circulation models formulated on unstructured meshes offer multi-resolution functionality in a seamless way
A number of Finite-Element Sea ice–Ocean circulation Model (FESOM)-based studies related to the impact of local dynamics on the global ocean indicate that the multi-resolution approach advocated by FESOM is successful and allows one to explore the impact of local processes on the global ocean with moderate computational effort
FESOM1.4 (Wang et al, 2014) already offers a very competitive throughput compared to structured-mesh models in massively parallel applications (Sein et al, 2016), we continue to explore the ways to further increase the numerical efficiency of unstructured-mesh models and extend their area of applicability
Summary
Ocean circulation models formulated on unstructured meshes offer multi-resolution functionality in a seamless way. They are common in coastal ocean modeling, they are only beginning to be used for global ocean studies. This paper describes the new numerical core of FESOM2, which is based on finite-volume discretization. The main reason for switching to a new finite-volume numerical core in FESOM2 is its higher computational efficiency. It stems largely from a more efficient data structure.
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