A large-scale high-resolution numerical model for sea-ice fragmentation dynamics

Abstract. Sea ice motion and fragmentation forecasts are of vital importance for all human interaction with sea ice, ranging from indigenous hunters to shipping in polar regions. Sea ice models are also important for modelling long term changes in a warming climate. Here we apply a discrete element model (HiDEM), originally developed for glacier calving, to sea ice break-up and dynamics. The code is highly optimized to utilize high-end supercomputers to achieve extreme time and space resolution. Simulated fracture patterns and ice motion are compared to satellite images in the Kvarken region of the Baltic sea in March 2018. A second application is ice ridge formation in the Bay of Riga. With a few tens of graphics processing units (GPUs) the code is capable of reproducing observed ice patterns, that in nature may take a few days to form, over an area ∼ 100 km × 100 km, with an 8 m resolution, in computations lasting ∼ 10 hours. The simulations largely reproduce observed fracture patterns, ice motion, fast ice regions, floe size distributions, and ridge patterns. The similarities and differences between observed and computed ice dynamics and their relation to initial conditions, boundary conditions and applied driving forces are discussed in detail. The results reported here indicate that HiDEM has the potential to be developed into a high-resolution detailed model for sea ice dynamics over short time scales, which combined with large-scale and long-term continuum models may form an efficient framework for sea ice dynamics forecasts.