Advances in understanding ice–ocean stress during and since AIDJEX

Variation of ice/ocean drag (momentum exchange) is an important yet often overlooked aspect of pack ice modeling. It is commonly parameterized as proportional to the square of the velocity difference between the ice and the undisturbed ocean, often with a constant angle offset to account for rotational effects in the ice–ocean boundary layer. This approach is critiqued in light of extensive observations that have revealed the underlying turbulence scales governing momentum exchange within the IOBL. Fluid dynamical similarity implied by these scales provides a framework for addressing several factors that affect the drag relationship, including variation in ice roughness, relative drift speed, buoyancy flux at the ice/ocean interface, and stratification in the upper ocean. These are examined and discussed in light of recent changes in the Arctic ice pack. The drag law is formulated in terms of dimensionless surface velocity, which in its simplest form is called Rossby similarity, and accounts explicitly for variation in undersurface hydraulic roughness, z0. A generalization that includes interfacial buoyancy flux is also described and illustrated, and the impact of near surface ocean stratification is discussed. Estimates of z0 based on underice measurements vary widely; by a combination of observations and simple IOBL modeling, an attempt is made to reduce these to a manageable set associated with distinct ice types.

► Effective drag and turning angle decrease with increasing ice velocity. ► Buoyancy from interfacial melting can significantly decrease drag. ► Shallow pycnoclines (mixed-layer depth) may alter the deflection angle. ► Basal hydraulic roughness is the primary determinant of drag coefficient. ► Recent changes significantly affect ice/water stress parameterization.