Regional sensible and radiative heat flux estimates for the winter Arctic during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment

We estimate the influence of the mosaic distribution of surface temperature s of sea ice on regional surface sensible and radiative heat fluxes on the basis of advanced very high resolution radiometer (AVHRR) temperatures. The AVHRR data were used to derive similar to 1 km(2) surface temperature valu es for 100 x 100 km(2) regions. Regional flux estimates are compared to dir ect flux measurements taken during the Surface Heat Budget of the Arctic Oc ean (SHEBA) experiment in the Beaufort Sea. We describe 48 cases of clear-s ky conditions between December 1997 and February 1998. The distribution of surface temperatures within each region is skewed: most temperatures fall n ear the value observed at the ice camp, but the distribution has a warm tai l corresponding to subregions with thinner ice. Sensible heat fluxes at the ice camp were downward, from the air to the ice; Although the camp was rep resentative of the majority of the region, the upward flux from thin ice ge nerally balanced the downward flux to thicker ice, suggesting a regional eq uilibrium of near-zero sensible heat flux. This was true whether the net do wnward flux at the camp was large or small or whether the ice was less comp act, as in January, or more compact, as in December and February. The only exception to this generalization occurred when the ice was under strong com pression. The net regional radiative loss from the ice surface was similar to 22% greater than that measured on the flee at the SHEBA camp. This incre ase is due to the fourth-power temperature dependence of the radiative flux acting on the skewed distribution of surface temperatures. The implication s for modeling are that sea ice tends toward small net surface sensible hea t flux on an aggregate scale, an emergent property of the system, and that parameterizing the regional mosaic of surface temperatures to resolve corre ctly the radiative balance in winter is important.