Sheltering of sea ice ridges in the ice-ocean drag force: implications from laboratory experiments

Abstract

The increasing movement and deformation of Arctic sea ice cover results in pronounced drag sheltering effects behind sea ice pressure ridges. This needs to be accounted for in the parameterization of the form drag of ridges, thereby posing a challenge to evaluate the ice–ocean dynamic feedback. Laboratory experiments were conducted in a water tank to explore the sheltering effect between adjacent ridges of various geometries. The form drag forces on the keel models were measured, and the particle image velocimetry (PIV) system was employed to capture the flow fields surrounding the models to explain the variations in the drag force. The key sheltering parameters were the ratio between keel spacing and keel depth L/H, flow velocity u, and keel slope angle α. The results showed that the drag force F1 on the upstream keel was close to the value of the single keel case, while the drag force F2 on the downstream keel was lower, for L/H ≤ 10 even opposite to the flow direction. Having changed from negative to positive, the sheltering coefficient Г = F1/F2 increased with increasing L/H. Г decreased remarkably with steepening α and was independent of u. To fully incorporate the effects of the L/H and α , we propose a new sheltering function fitted with the experimental results:Г =[1-1.56exp(sL/H)]*1.20α-0.08, s=0.001α-0.15. This function is compared with the previous sheltering functions and the actual ice conditions in the Arctic Ocean, pointing the way to obtain the final sheltering functions applicable to sea ice dynamics models.