A parameterization of the ice‐ocean drag coefficient

Abstract

A parameterization of the ice‐ocean drag coefficient (Cw) was developed through partitioning the oceanic drag force into three components: (1) form drag on the floe edge, (2) form drag on the ridge keel, and (3) skin friction on the ice bottom. Through these quantities, Cw was expressed as a function of observable sea ice geometric parameters. Sensitivity studies were carried out to investigate the influence of varying sea ice conditions on Cw. The results revealed that Cw increases first and then decreases with increasing ice concentration (A), similar to the observations of the air‐ice drag coefficient, and which is mainly attributed to the nonmonotonic variation of the form drag on the floe edge with ice concentration. Moreover, the form drag on the floe edge is always the dominant component, having a proportion of more than 60% in sea ice with a large aspect ratio (draft/length ≥ 1/100), indicating the necessity of including this term in sea ice dynamic models, particularly for the marginal ice zone (MIZ). The form drag on the ridge keel becomes dominant only when the ridging intensity is extremely high (depth/spacing ≥ 1/20). Additionally, a large value of Cw cannot be caused only by the inclusion of form drag terms but also by large skin friction over rough ice bottoms. Finally, for typical situations in the MIZ with moderate ridging intensity, the parameterization will underestimate Cw by approximately 30% for a rough ice bottom and by over 80% for a smooth ice bottom if no form drags are considered.