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

The ice-ocean drag coefficient $$ and turning angle $$ 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 $$ and $$ 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 $$  = 1-130 $$ 10^-3 and $$  =  - 19-1° at 5 m depth. Comparing different stations, the observations suggest a pronounced dependence of $$ on the stability parameter ( $$ ) resulting from mechanical and buoyant forcing. $$ rapidly decays with increasing $$ , indicating that the ice-to-ocean momentum transfer is enhanced for neutral or unstable conditions, while it is weakened for stable conditions. In addition, observed vertical profiles of currents revealed that $$ 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.