A HIGH RESOLUTION GRANULAR SEA ICE MODEL Mark Hopkins CRREL The Arctic ice pack is composed of parcels of first-year and multiyear ice divided by leads and pressure ridges. In the past, with interest focused on basin-scale processes, sea ice models have used continuum descriptions of sea ice rheology. With the current focus on resolution approaching the scale of individual floes and failure processes that define large-scale rheology, it makes sense to develop a model that incorporates this level of detail. I am presently developing a high-resolution granular sea ice model. I propose to integrate this granular model into the PIPS-3.0 large-scale sea ice model. As I envision it, the granular sub-model would replace one or more cells in the large-scale ice model. The large scale model would furnish the boundary conditions on ice transport and boundary motions needed to drive the granular model. The granular model would allow high resolution simulation of areas of interest in the central Arctic or in coastal regions. The granular model is based on a discrete element approach in which individual parcels of first-year and multiyear ice are explicitly modeled. In a nutshell, the granular model takes the continuum assumption from the pack scale down to the floe scale. The yield surface and flow rule which are of paramount importance for large-scale models are not needed in a granular model. They are replaced by floe scale failure processes. The individual ice parcels may freeze together, overlap to raft or form pressure ridges, split or separate to form leads depending on the dynamic conditions. Coulomb frictional forces resist sliding between ice parcels. The model ice pack is driven by boundary deformations, winds and currents. Because the model explicitly simulates an assembly of thousands of ice parcels with a distribution of sizes, shapes, and thicknesses it is inherently anisotropic. In its current form the granular model is capable of simulating a 50 km x 50 km area of the ice pack at a rate of about 1 minute of CPU time per day on a desktop computer. Advantages of a Granular Model: ( Spatial resolution at the scale of individual ice parcels. ( Surface stress resolution at the scale of individual ice parcels. ( Internal stress resolution with 'smart' FEM floes. ( Direct coupling of floes with wind and water drag. ( Explicit location and energetics of ridge formation allows integration with ambient noise models. ( Unlimited scalability: As computer power increases so can scope and detail. ( The ability to directly incorporate SAR data into simulations. ( The ability to integrate parameterizations of smaller-scale behavior such as freeze and melt, ridging, rafting, and floe splitting. ( A natural transition between a fully consolidated pack and the 'loose' conditions of the MIZ and the late summer pack. Figure 1: A snapshot from a simulation in which a 200 km x 200 km model ice pack is undergoing simple shear with dilatation. Large-scale lead development is evident. The strain rates are (u/(y=1.0x10-6 /s and (v/(y = 0.5x10-6 /s. Figure 2: A snapshot from the same simulation showing the lines of force propagating through the model ice pack. The black lines represent compressive forces and the red lines represent tensile forces. The line width is proportional to the magnitude of the force. An animation of this simulation can be viewed on the WEB at the following location: www.crrel.usace.army.mil/ierd/hop1/seaice.html