MODELING THE THERMODYNAMICS OF A SEA-ICE THICKNESS 1 - SENSITIVITY TOICE THICKNESS RESOLUTION

A one-dimensional ice thickness distribution model is presented to det ermine the minimum number of ice thicknesses necessary to resolve the area-averaged annual cycles of ice thickness and turbulent fluxes. The baseline case includes 40 ice thickness categories; ice thickness and area, meltwater ponds, ice salinity and age, snow cover, and surface albedo evolve independently for each ice category. A ridging and ice e xport parameterization, and a coupled one-dimensional ocean mixed laye r model are also included. Sensitivity studies indicate that 16 ice th ickness categories can accurately resolve the baseline annual cycles o f area-averaged ice thickness and the summertime turbulent fluxes in t his model, provided that one third of the thickness categories represe nt ice thinner than 0.8 m. Resolving the distribution of ice in this t hickness range is important in simulating the area-averaged ice charac teristics. Wintertime values of the turbulent fluxes differ from the b aseline by up to 1 W m(-2) for fewer than 40 ice thickness categories. The large difference in turbulent fluxes between open water and ice t hicker than 1.6 m makes the area-averaged value sensitive to the numbe r of ice thickness categories ies, since this number can affect the ca tegories that are merged, the categories that melt completely, ice tha t is ridged, and the resolution of the ice thickness distribution. Thi s makes an accurate simulation of the baseline wintertime turbulent fl uxes difficult. Model simulations with fewer than 40 categories provid e a reasonable estimate of the baseline response to a surface longwave heat flux perturbation of greater than 5 W m(-2). The annually area-a veraged ice thickness is within 10 cm. The model response to a heat fl ux perturbation of less than 5 W m(-2) is similar for a wide range of ice thickness categories, since the thickness distribution of ice thin ner than 1 m is not affected.