Parameterizing the Sheltering Effect of Ice Ridges on Ice–Ocean Drag in Polar Oceans: Insights from Numerical Simulations

Abstract In recent decades, ice ridge formation has become more frequent in the polar oceans, constituting substantial areal fractions of sea ice. Ridges enhance air–ocean momentum transfer and modify sea ice drift patterns by altering ocean drag forces. Dynamic interactions between ridges and ocean currents trigger a keel sheltering effect (KSE), reducing ice–ocean drag. Quantifying the KSE under full-scale conditions remains challenging due to technological limitations. To address this gap, we conducted computational fluid dynamics (CFD) simulations of KSE, building on our previous findings from laboratory experiments. Simulations showed that the sheltering function Г (upstream/downstream keel drag ratio) is negatively correlated with keel intensity ( H / L , keel depth/spacing ratio), keel angle ( α ), and dimensionless depth ( D / H , water depth/keel depth ratio). When D / H ≥ 25, Г approached an asymptotic constant independent of D / H , resembling deep-water conditions. For an average α of 30°, an increase in keel intensity from typical to clustered keel spots ( H / L from 0.01 to 0.10), resulted in a decrease of Г from 0.91 to 0.36. By taking into account Г, the refined parameterizations of the keel and the ice–ocean drag coefficient revealed that the KSE reduced the ice–ocean drag coefficient by 4%–64% as H / L increased. Neglecting KSE would lead to an average of 23% underestimation of sea ice drift speed and a 4° shift in the drift direction for the full α range between 10° and 90°. A new parameterization of the ice–ocean drag coefficient accounting for the distribution of α was proposed for sea ice dynamics modeling. This improves the simulation performance in scenarios with high keel intensity and ice concentration.