RIDGING AND STRENGTH IN MODELING THE THICKNESS DISTRIBUTION OF ARCTICSEA-ICE

A theory describing evolution of the ice thickness distribution (the p robability density of ice thickness) was proposed by Thorndike et al. (1975) and has been used in several sea ice models. The advantage of t his theory over the widely used two-level formulation is that it treat s ridging explicitly as a redistribution of ice thickness, and ice str ength as a function of energy losses incurred by ridge formation. Howe ver, the parameterization of these processes remains rather speculativ e and largely untested, arid so our purpose here is to explore these p arameterizations using a numerical model based on this theory. The mod el uses a 160-km resolution grid of the Arctic and 7 years of observed atmospheric forcing data (1979-1985). Monthly oceanic heat flux and c urrent fields are obtained from a 40-km resolution coupled ice-ocean m odel run separately with the same forcing. By requiring the computed m onthly mean ice drift to have the same magnitude as observed buoy drif t, we estimate the primary strength parameter: the ratio of total to p otential energy change during ridging. This ratio depends on the value of other parameters; however, the standard case has a ratio of 17 whi ch is within the range estimated by Hopkins (1994) in simulations of i ndividual ridging events. The effects of ridge redistribution and shea r ridging parameters are illustrated by a series of sensitivity studie s and comparisons between observed and modeled ice thickness distribut ions and ridge statistics. In addition, these comparisons highlight th e following shortcomings of the thickness distribution theory as it is presently implemented: first, the process of first-year to multiyear ridge consolidation is ignored; and second, the observed preferential melt of thick ridged ice is not reproduced.