Linking ridge shapes to the ice thickness distribution via discrete element simulations

Abstract. Ridges significantly increase the sea-ice thickness compared to the level ice surrounding them. In continuum sea-ice models, this increase is either represented by an increase in mean ice thickness or by changes in the ice thickness distribution (ITD). The implementation of ITDs requires a sub-grid parametrization of ridging by using a redistribution scheme. In contrast, the discrete element method (DEM) enables explicit simulations of ridge formation process, including ice fragmentation into rubble and its subsequent redistribution to ridges. Here, we use a DEM model to simulate ridging across a sea ice domain of size 6 km x 6 km. The DEM simulations yield deformed ice cover with ridges of varying shapes, namely triangular and trapezoidal ridges; the trapezoidal ridges notably affect the ITD of the deformed ice cover by creating a bump in the ITD towards thicker ice. We find that the ITD of the deformed ice field from DEM simulations differs from those from the continuum model, that uses only mean thickness, and from two commonly used ridging functions within redistribution schemes used as sub-grid parametrizations. Further, we show how to formulate an analytical redistribution function that captures the effect of various ridge shapes and discuss when it could replace existing ridging schemes. Our results demonstrate that an improved representation of ridging is needed within continuum models to resolve ridges both with their depth and shape within the ITD, especially in high spatial resolutions. Additionally, we formulate open questions in need of answers to allow implementation of our new distribution of ridged ice into continuum models, which connect to the ridging process itself.