ON THE MESOSCALE INTERACTION OF LEAD ICE AND FLOES

The plasticity of the Arctic ice pack depends on its granular nature, in particular on the size and distribution of areas of thin ice and op en water surrounding multiyear ice flees. The paper begins with constr uction of a mesoscale (10-100 km) granular model of the central Arctic ice pack. The mesoscale model is based on a dynamic particle simulati on in which individual multiyear ice floes and surrounding parcels of first-year ice are explicitly modeled as discrete, convex polygons in a two-dimensional domain. Deformation of the domain produces areas of localized failure and areas of open water. The areas of localized fail ure are modeled as pressure ridging events using the results of numeri cal experiments performed with a computer simulation of the ridging pr ocess. The paper focuses on the results of numerical experiments perfo rmed with the mesoscale model. In the experiments the model ice pack i s biaxially deformed at constant strain rates. The principal strain ra tes are varied to create deformation states ranging from pure shear to uniform compression. The results define the shape and magnitude of th e plastic yield surface, the strain rate vectors associated with point s on the yield surface, the partition of energy dissipation between ri dging and in-plane sliding, and the changes in the ice thickness distr ibution associated with various deformation states.