Sea Ice Ridging Schemes

Abstract

As sea ice is advected on the surface of the ocean, the ice concentration (0 ≤ A ≤ 1) and the mean ice thickness change in response to thermodynamic and mechanical forcing. In this paper the authors review the existing advection schemes and compare their properties in the absence of thermodynamic effects. In Hibler's classical scheme, the ice area fraction at a material particle changes due to the divergence of the large-scale horizontal velocity field, and a further constraint is applied in order to keep A ≤ 1. This scheme is used in almost all sea ice models, although Hibler and Shinohara have both since included a ridging sink tem In this paper the authors show that the Hibler advection scheme is a special case of Gray and Morland's ridging model and compare the ridging schemes of Hibler and Shinohara with the simple scheme of Gray and Morland. It is demonstrated that the Hibler scheme still allows ice concentrations to exceed unity in maintained convergence and that both Hibler and Shinohara schemes admit the possibility of negative ice concentrations during maintained shearing. A general framework is formulated for the functional form of the ridging sink term that guarantees 0 ≤ A ≤ 1. Finally, some elementary analytic solutions are derived, which imply that, if ridging is independent of shear effects, quantities are conserved along particle paths.