Simulating sea-ice deformation in viscous-plastic sea-ice models with CD-grids

Linear Kinematic Features (LKFs) are found everywhere in the Arctic sea-ice cover. They are strongly localized deformations often associated with the formation of leads and pressure ridges. Viscous-plastic sea-ice models start to produce LKFs at high spatial grid resolution, typically with a grid spacing below 5 km. A recent study showed that the placement of the variables on the grid plays an important role for the number of simulated LKFs. The study found that a nonconforming finite element discretization with a CD-grid placement (CD1) resolves more LKFs per degree of freedom compared to more common A,B and C-grids. A new CD-grid formulation (CD2) has just been proposed based on a conforming subgrid discretization. To analyze the resolution properties of the new CD2 approach we evaluate runs from different models (e.g FESOM, MPAS) on a benchmark problem using quadrilateral, hexagonal and triangular meshes. We found that the CD1 setup simulates more deformation structure than the CD2 approximation. This highlights the importance of the type of spatial discretization for the simulation of LKFs. Due to the higher number of degrees of freedom both CD-grids resolve more LKFs than traditional A,B and C-grids at fixed mesh level. This is an appealing feature as high spatial mesh resolution is needed in viscous-plastic sea-ice models to simulate LKFs.