Dependency of the drag coefficient on boundary layer stability beneath drifting sea ice in the central Arctic Ocean

Abstract

Abstract The ice-ocean drag coefficient $$C_{w}$$ C w and turning angle $$\theta_{w}$$ θ w are crucial parameters in ice-ocean coupled simulations, determining the transfer of momentum between the two media. These parameters are often treated as constants regardless of the static stability at the ice-ocean interface. This study investigates the variability of $$C_{w}$$ C w and $$\theta_{w}$$ θ w based on direct observations of thermal and kinetic energy balance. The observations were conducted beneath multiyear ice packs widely across the central Arctic during a period transitioning from ablation to refreezing, indicating significant variability of $$C_{w}$$ C w = 1–130 $$\times$$ × 10−3 and $$\theta_{w}$$ θ w = − 19–1° at 5 m depth. Comparing different stations, the observations suggest a pronounced dependence of $$C_{w}$$ C w on the stability parameter ( $$\mu$$ μ ) resulting from mechanical and buoyant forcing. $$C_{w}$$ C w rapidly decays with increasing $$\mu$$ μ , indicating that the ice-to-ocean momentum transfer is enhanced for neutral or unstable conditions, while it is weakened for stable conditions. In addition, observed vertical profiles of currents revealed that $$|\theta_{w}|$$ | θ w | tends to be smaller for unstable and larger for stable conditions. We suggest that numerical simulations using constant values could result in an underestimate of large-scale near-surface currents during the ice growing period.

Keywords

• Ice-ocean boundary layer
• Drag coefficient
• Turning angle
• Static stability
• Heat balance
• Sea ice dynamics