FY 1989

Modeling ice dynamics of coastal seas

Overland, J.E., and C.H. Pease

J. Geophys. Res., 93(C12), 15,619–15,637, doi: 10.1029/JC093iC12p15619 (1988)

A coupled sea ice, barotropic ocean model with a 1-km resolution and a seaward domain of 200 km quantifies three coastal processes: coupling of ice motion to wind-driven coastal currents, ice thickness redistribution under compaction at the coast, and formation of coastal shear zones. The model consists of an ice momentum balance, mass concentration and two-parameter ice thickness distribution, and equations for horizontal water motion and continuity using vertical structure functions. An appropriate constitutive law appears to be a hardening plastic based on qualitative observations from Alaskan continental shelves. For first-year sea ice, strength is taken to be proportional to the square of ice thickness. A north wind example of 10 m/s with the coastline to the west shows the depth dependence of rotational shear in the sea ice/ocean boundary layer and sea surface tilt which contributes an alongshore slope current. There is slight convergence of sea ice over the shelf, a coastal shear zone of 4 km, and an alongshore ice speed seaward of the shear zone of 6% of the wind speed caused by the combination of an under-ice shear layer and an alongshore slope current. For an onshore wind, ice is near free drift at 3% of the wind seaward of a ridging front, which propagates seaward. A square dependence of ice strength on thickness is required for the rubble field to approach a limiting thickness, consistent with observations. The hardening plastic interpretation of the rubble field has the stress state at the yield limit in contrast with a rigid plastic of high constant strength that yields only at the coast. We conclude that (1) ice thickness/motion feedback is important on scales less than 10 km, (2) the observational base to discriminate between mesoscale constitutive laws is not yet available, and (3) the relation of ice velocity to wind stress is variable because the ocean slope current responds only to the alongshore component of the wind.