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A Parameterization of the Lead-Width Distribution and Surface Turbulent Heat Flux for sea ice |
University of Colorado-Boulder
alam@cloud.colorado.edu
We have used submarine ice draft data to develop a parameterization for lead width distribution in arctic sea ice. This parameterized distribution is used to determine surface turbulent heat fluxes in a grid cell of a sea ice model. Our results indicate that for ice with thickness in the range of 0-30 cm, the width distribution can be defined in terms of known dynamic/thermodynamic sea ice model grid scale variables. For open water leads, the width distribution is represented by a mean open lead width and has been obtained in terms of open water fraction which is a known variable in a large-scale sea ice model grid. We have determined that dividing the ice into thickness categories of 0-0.3 m, 0.3-0.5 m, 0.5-0.8 m and a thick ice category that contains all ice thicker than 0.8 m, is sufficient to determine grid-scale averaged surface turbulent heat fluxes. The surface turbulent fluxes are computed from an algorithm based on surface renewal theory. In order to parameterize the fetch-dependent fluxes from open water and frazil ice, we have determined the mean open water width and the width distribution of frazil ice from observed or modeled grid-scale fractional coverage of open water and frazil ice. A dynamic/thermodynamic sea ice model cell calculates the fraction of area covered by the different ice thicknesses. Therefore we have parameterized the surface turbulent heat flux based on the surface fractional coverage of the above three categories of new and young (seasonal) ice and one thick ice category which consists of all ice thicknesses greater than or equal to 80 cm. The parameterized surface fluxes obtained by considering these four ice categories and an open water category match the accurately determined surface fluxes obtained by considering the detailed submarine tracks with a 1 m spatial resolution in ice draft data.
