A New Lagrangian Model of Arctic Sea Ice

A new Lagrangian sea ice model for the Arctic Ocean has been developed to accommodate the assimilation of integral measures of ice displacement over periods of days or weeks. The model is a two-layer (thick ice and open water) dynamic model with 600–700 cells spaced at roughly 100 km. 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, which determines the spatial derivatives of the velocity by a weighted summation of the velocities of adjacent cells. A length scale of 150 km is used. The model is driven with observed geostrophic winds and climatological-mean ocean currents. Ice growth and melt are found from a seasonaland thickness-based lookup table because the current focus is on the model dynamics. The model ice velocity simulations are compared to observed buoy motion. Over the 5-yr period 1993–97 the correlation of the daily averaged model velocity with buoy velocities is R 5 0.76 (N 5 42 553, rms difference 5 0.072 m s21, speed bias 5 10.009 m s21, angle bias 5 8.08). This compares favorably with the correlation of a state-of-the-art Eulerian coupled ice–ocean model, where R 5 0.74 in the summer and 0.66 in the winter over the same 5-yr period.