EVOLUTION OF NEW ICE AND TURBULENT FLUXES OVER FREEZING WINTER LEADS

A model is presented that describes the coevolution of surface turbule nt fluxes and new ice growth during the freezing of leads. The model i ncludes a sophisticated parameterization of the surface sensible and l atent heat fluxes. The new ice growth model distinguishes between the congelation and frazil regimes. During frazil growth, heat loss from t he open water part of the lead results in formation of new ice which i s advected to the downwind edge. With time, the ice edge extends to th e upwind lead edge, and the lead is gradually covered with ice. Over t he ice-covered portions, the turbulent heat loss results in ice consol idation, and thereafter ice growth occurs, The turbulent heat flux dep ends on the surface characteristics which vary across the lead surface during frazil growth. Therefore in the frazil regime, ice concentrati on, ice thickness, surface temperature, and the surface turbulent flux vary across the lead surface. Even after consolidation, frazil ice ha s a different surface roughness length from congelation ice for the sa me ice thickness up to an ice thickness of 10 cm. We have used this mo del to determine the evolution of surface turbulent heat fluxes under various atmospheric conditions and for different lead widths. In the f razil regime, there is a considerable fetch dependence of the surface characteristics, as the ice is advected to the downwind edge and slowl y covers the entire lead. This fetch dependence is greatest for the hi gher wind speeds and larger lead widths. There is significantly higher ice production under conditions when frazil formation occurs because the ice transport to the downwind edge leaves the surface of the lead open, allowing the warmer sea surface to exchange heat with the atmosp here. The rapid growth rates result in large salt release to the ocean , with implications for ocean dynamics. We have done a sensitivity stu dy to investigate the effect of oceanic heat flux at the underside of the ice, which results from the salt rejection upon ice formation in f reezing leads, on the evolution of new ice and turbulent fluxes.