Observations and model calculations of aerodynamic drag on sea ice in the Fram Strait

Wind and temperature profiles in the constant flux layer obtained by tethersonde were used to compute the total aerodynamic drag on an area of 60% pack ice in the Fram Strait (79°20’N, 1-3°W). The boundary layer appeared adiabatic to heights greater than 150 m, and there were only minor air/water temperature differences. Drag coefficients of 4.9 and 5.1 × 10^-3 referred to 10 m above ground level were found. Eddy correlation measurements in the local constant flux layers over ice floes were used to estimate the skin drag of an area of 100% ice cover. This was less than 40% of the total drag on the actual area. The corresponding drag coefficient was 1.4×10^-3. A drag partition model is proposed for computing the total drag over an area of pack ice as a function of ice concentration, mean freeboard and length of the ice floes, and typical roughness lengths of ice and sea surfaces. The model predicts maximum form drag at 73% ice concentration for floes of the type observed in the Fram Strait.