Split-explicit external mode solver in finite volume sea ice ocean model FESOM2
Abstract. A novel split-explicit (SE) external mode solver for the Finite volumE Sea ice–Ocean Model (FESOM2) and its sub-versions (example 2.5) is presented. It is compared with the semi-implicit (SI) solver currently used in FESOM2. The split-explicit solver utilizes a dissipative asynchronous (forward–backward) time-stepping scheme. Its implementation with Arbitrary Lagrangian-Eulerian vertical coordinates like Z-star (Z ∗) and Z-tilde (Z˜) is explored. The comparisons are performed through multiple test cases involving idealized and realistic global simulations. The SE solver demonstrates lower phase errors and dissipation, but maintain a simulated mean ocean state very similar to the SI solver. The SE solver is also shown to possess better run-time performance and parallel scalability across all tested workloads.
Model code and software
FESOM2.5 with preliminary Split-Explicit Subcycling https://zenodo.org/doi/10.5281/zenodo.10040943
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