ON THE RIDGING OF INTACT LEAD ICE

The sea ice pressure ridging process is modeled using a two-dimensiona l particle simulation technique. In this model, blocks are broken from an intact sheet of relatively thin lead ice driven against a thick, m ultiyear floe at a constant speed. The blocks of ice rubble accumulate to form the ridge sail and keel. The energy consumed in ridge growth, including dissipation, is explicitly calculated. A series of numerica l experiments are performed to establish the dependence of the energet ics on the thickness of the ice sheet and the friction between blocks. The results suggest that the total energy required to create a pressu re ridge is an order of magnitude greater than the potential energy in the ridge structure. A typical sea ice cover in the polar regions con tains a variety of ice thicknesses that evolve in response to both dyn amic and thermodynamic forcing. The variable thickness of the ice cove r is created by deformation, which simultaneously causes formation of thick ice through ridge building and thin ice through lead creation. S ince the energy expended in deformation is largely determined by the r idging process, an understanding of the energetics of pressure ridging is critical in the determination of ice strength on a geophysical sca le.