Comparison of Observed and Modeled Ice Motion in the Arctic Ocean

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Abstract
Daily maps of multiyear ice concentration, derived from Nimbus-7 SMMR passive microwave data, are analyzed to obtain the displacement of the multiyear ice edge and information on the convergence/divergence within the pack. The dynamic—thermodynamic sea-ice model of Hibler (1979) is run with daily time steps and with forcing by the interannually varying fields of geostrophic wind and temperature-derived thermodynamic fluxes. Model-data comparisons are made for the net drift during the months of November through January of the 1978—79, 1979—80, and 1980—81 seasons, and for the shorter-term drift during a 52 day period. Both the model and the data-based drifts for the 25 November 1978 to 28 January 1979 period differ from the classical Beaufort-gyre pattern exhibited in the other two winters. For the 52 day period of November—December 1978, both the model and the data show an eastward drift followed by a westward drift of the ice edges in the Laptev Sea, and for the 25 November 1978 to 28 January 1979 period, a net westward drift of about 250 km. Overall, the model and the data exhibit the same patterns of ice movement with marked month-to-month and large interannual variations in the drift. Good agreement is found in most regions of the central Arctic, but pronounced discrepancies occur near the edge of the total ice pack in the East Greenland Sea. During a short period of large changes in multiyear ice concentration in the central Arctic around 2 December 1980, the divergence implied by the changes in multiyear concentration is qualitatively compared with the divergence computed from the modeled velocity fields. Both the microwave data and the model results indicate similar temporal characteristics of pack-ice response during this major deformation event.