Influence of a sea ice ridge on low-level airflow

The influence of a single pressure ridge of 4.5 m height on the structure of the atmospheric surface layer is studied. The field of the mean wind velocity is governed by typical features of a Bernoulli effect with a speedup over the crest and a shadowing effect downwind of the ridge. It is found that the turbulence generated by the ridge compensates for the deformation of the flow field by mixing momentum downward. Both mean and turbulent fields are restored to their upwind values at a distance of similar to 300 m downwind of the ridge, which is equivalent to an aspect ratio of similar to 0.015. The level of maximum turbulence generated by the ridge is characterized by a linear relationship. A formulation for the determination of the form drag of a single ridge is proposed and generalized toward an ensemble of ridges. We estimate that the form drag contributes <50% to the total drag exerted by a typically ice covered sea surface on the atmospheric flow.