Sharper Resolution of Arctic Sea Ice Dynamics with Non-Conforming Finite Elements in FESOM2

Sea ice dynamics in numerical models are discretized on a spatial grid, with variables located at grid cell vertices, edges, or centers. On triangular grids, the number of edges is three times larger than the number of vertices. Consequently, placing variables on edges --- corresponding to a non-conforming finite-element discretization --- increases the number of degrees of freedom and effectively enhances the spatial resolution on a given mesh. Idealized benchmark experiments without a coupled ocean using the CD-grid discretization, where sea ice velocity is placed on edges and tracers on vertices, have demonstrated an increased occurrence of small-scale fractures and more finely resolved features in the sea ice field compared to other discretizations. In this study, we present the first application of the CD-grid in a high-resolution, fully coupled sea ice--ocean simulation using FESOM2, using a spatial resolution in the Arctic of 4.5 km. We show that the CD-grid produces a more sharply resolved sea ice field with an increased occurrence of small-scale structures relative to the A-grid configuration, in which both velocity and tracers are placed on vertices, while maintaining the same large-scale sea ice characteristics. In addition, we present a scaling analysis of the CD-grid in parallel applications across varying core counts, including runtime benchmarks and a direct performance comparison with the A-grid.