Wind drag coefficient over first‐year sea ice in the Bering Sea

Abstract

Profiles of relative wind speed and temperature were collected from four levels over rough sea ice in the marginal ice zone of the Bering Sea and used to compute surface wind drag coefficients. Based upon 138 profiles for near‐constant ice conditions, northeast winds of 3–15 m s −1 , and near‐neutral stability, the mean, near‐neutral, 10‐m drag coefficient was 0.00309±0.00049. This is among the largest drag coefficients measured for neutral atmospheric conditions over sea ice. Sixty‐five percent of the variance of this estimate is explained by orientation of the ice floe to the wind; an additional 5% of the variance is explained by wind‐speed dependence. Provided that diabatic atmospheric stability over the Bering Sea ice pack is well correlated with low wind speed, the significant ice‐advecting wind stress on the ice is determined from the neutral value of the drag coefficient, a function of ice roughness length alone. The ice forecaster thus may use remote measurements or estimates of wind speed and surface roughness to assess the wind component of ice advection.