A new Lagrangian model of sea ice

We have developed a new Lagrangian sea ice model for the Arctic Ocean. The model is designed to accomodate the assimilation of trajectory data such as that from the RGPS. The model is a two-layer dynamic model with 600 to 700 cells, each roughly (100 km)^2 in area. The force balance equation is solved for each cell with standard wind and water stress terms, a Coriolis term, and an internal ice stress term. The internal stress is found using a viscous-plastic rheology and an elliptical yield curve. The strain rate is determined by the Smoothed Particle Hydrodynamics formalism. The spatial derivatives of the velocity are found over a scale of 150 km. The model is driven with observed geostrophic winds and climatological ocean currents. The growth and melt rates are found from a seasonal- and thickness-based table since the focus at this point is on the dynamics. The model velocity field is compared to that of buoys. Over a two-year period the correlation of the daily averaged model velocity with the buoy velocities is R=0.76 (N=12,233, RMS difference=0.074 m/s). This compares favorably with the correlation of a state-of-the-art Eulerian model where R=0.74 in the summer and 0.66 in the winter over a five-year period (N=18,605, RMS difference=0.070 m/s in both seasons) (Zhang et al., 2002).