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

• Published in: Scientific Reports
• Main Authors: Kawaguchi, Yusuke, Hoppmann, Mario, Shirasawa, Kunio, Rabe, Benjamin, Kuznetsov, Ivan
• Format: Article in Journal/Newspaper
• Language: English
• Published: Nature Publishing Group 2024
• Subjects: Arctic Ocean; Drag coefficient; Heat balance; Ice-ocean boundary layer; Sea ice dynamics; Static stability; Turning angle; Sea ice
• Online Access: https://doi.org/10.1038/s41598-024-66124-8; https://pubmed.ncbi.nlm.nih.gov/38965366; https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11224423/

The ice-ocean drag coefficient Cw and turning angle θw 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 Cw and θw 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 Cw = 1-130 × 10-3 and θw = - 19-1° at 5 m depth. Comparing different stations, the observations suggest a pronounced dependence of Cw on the stability parameter ( μ ) resulting from mechanical and buoyant forcing. Cw rapidly decays with increasing 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 |θw| 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.