[A-CG42] Science in the Arctic Region

[ACG42-09] Dependency of ice-ocean drag coefficient on boundary layer stability in Central Arctic Ocean

*Yusuke Kawaguchi ¹, Benjamin Rabe ², Ivan Kuznetsov², Mario Hoppmann², Kunio Shirasawa³ (1.Atmosphere and Ocean Research Institute , 2.Alfred Wegener Institute , 3.Institute of Low Temperature Science )

Keywords:Arctic Ocean , turbulent flux, eddy covariance , ice-ocean boundary layer

The ice-ocean drag coefficient (Cw) is a crucial parameter in ice-ocean coupled simulations, determining transfer of momentum between the two media. In simulations, Cw is often set as a constant regardless of the diverse boundary conditions at the ice-ocean interface. This study investigated the variability of Cw based on eddy-covariance measurements for interfacial turbulent fluxes of heat and momentum beneath drifting pack ice. The observations were conducted extensively across the central Arctic Ocean during a period when the ice-ocean interface transitioned from ablation to refreezing. Upon comparing different stations, the observation suggests a pronounced dependence of Cw on the stability parameter (μ) estimated from measured friction velocity and buoyancy flux. Cw exponentially decays with increasing μ, indicating that the ice-to-ocean momentum transfer is strengthen during unstable conditions and weaken during stable conditions. Numerical simulations with an invariant Cw would underestimate ice-ocean momentum exchange, leading to undermining of large-scale circulation of near-surface currents and sea-ice drift especially during the ice growing period.