FY 1987

The size of wind-driven coastal polynyas

Pease, C.H.

J. Geophys. Res., 92(C7), 7049–7059, doi: 10.1029/JC092iC07p07049 (1987)

The sizes of wind-generated coastal polynyas have been observed to be nearly constant for steady atmospheric conditions owing to the balance between the advection of sea ice away from the coast and the area-averaged production rate of new ice. A simple model is used to explore the relationship of several environmental parameters to the maximum size attained by the polynya and the speed at which the maximum is reached for a given atmospheric event. The model results suggest that size is strongly a function of air temperature, such that colder air produces a smaller polynya for a given offshore wind velocity. However, size is only moderately a function of wind speed, especially for winds greater than 10 m s^–1, since increasing the speed increases both the advection rate and the ice production rate. The model results are compared to observations made around a coastal polynya during February 1982 and 1983 along the southern coast of St. Lawrence Island in the northern Bering Sea and during February 1985 along the southern coast of the Seward Peninsula. The model correctly predicts the general maximum dimensions of these winter polynyas, although the atmospheric stationarity assumptions limit the usefulness of the predictions of the speed at which the maximum is reached. The results of this study suggest that the contribution of heat from the coastal ocean to the high-latitude winter atmosphere is a self-limiting process proportional to the amount of time the wind-driven ice drift has a component normal to the coast. This has important implications for the interpretation of satellite imagery for ice-covered oceans and for understanding high-latitude climate dynamics.