CD-type discretization for sea ice dynamics in FESOM version 2

Abstract. Two recently proposed variants of CD-type discretizations of sea-ice dynamics on triangular meshes are implemented in the Finite volumE Sea ice – Ocean Model (FESOM version 2). The implementations employ the finite element method in spherical geometry using longitude-latitude coordinates. Both of them rely on the edge-based sea-ice velocity vectors, but differ in basis functions used to represent velocities. The first one uses nonconforming linear (Crouzeix–Raviart) basis functions, and the second one uses continuous linear basis functions on subtriangles obtained by splitting parent triangles into four smaller triangles. Test simulations are used to show how the performance of the new discretizations compares with the A-grid discretization using linear basis functions. Both the CD discretizations are found to simulate a finer structure of linear kinematic features (LKFs). Only the first CD variant demonstrates some sensitivity to the representation of scalar fields (sea-ice concentration and thickness), simulating a finer structure of LKFs with the cell-based scalars than with the vertex-based scalars.