On Modeling the Weddell Sea Pack Ice

Abstract

Some results from a dynamic-thermodynamic simulation of the seasonal cycle of the Weddell Sea pack ice are described. The model used for the study is similar to that developed by Hibler (1979) for a numerical investigation of the Arctic ice cover. It employs a plastic ice rheology coupled to a two-level ice-thickness distribution. The thickness characteristics evolve in response to ice dynamics, and to ice growth and decay rates dictated by surface heat-budget calculations and by heat storage in a fixed depth oceanic boundary layer. Observed time-varying wind, temperature, and humidity fields based on the 1979 Australian analysis are used together with empirical radiation fields and fixed ocean currents to drive the model. Employing these fields, the model is integrated over two seasonal cycles. The second-year results are compared to observed ice-drift data obtained by Ackley (1981[b]) and to ice-edge characteristics determined from satellite imagery. In analyzing the results, particular attention is paid to ascertaining the relative roles of ice dynamics and thermodynamics in determining the ice-edge characteristics. A sensitivity analysis of the effect of a different parameterization of the atmospheric temperature and humidity fields is also carried out. Overall, the results suggest that (1) ice dynamics are essential in describing the seasonal cycle, and (2) a feedback between the atmospheric temperature and the presence of ice may be a major cause of the rapid decay of the Antarctic ice cover during the spring-summer period.