HIERARCHY AND SEA-ICE MECHANICS - A CASE-STUDY FROM THE BEAUFORT SEA

Hierarchy implies that the study of sea ice can be divided into analysis of subsets of processes based on scale and their interaction with adjacent scales. We apply these concepts to regional sea ice dynamics. The apparent self-similar property of ice floes seen in aircraft or satellite images argues for an aggregate nature of sea ice, that viscouslike regional behavior arises from discrete flee interactions. However, for some regions and some times, characteristic behavior, where lead patterns seen in basin-wide advanced very high resolution radiometer images appear to be related to coastal orientation hundreds of kilometers away, suggests that small regional scale processes O(10 km) and discontinuities in the velocity or stress state along boundaries can affect the larger-scale sea ice distribution and dynamics O(500 km). Thus sea ice displays both aggregate type behavior and discontinuous type behavior based on the history of forcing and shape of the enclosing basin. The appropriate matching of atmospheric processes to sea ice processes in air-ice interaction is through the sea ice deformation field rather than the response of ice velocity to the local wind. This is because atmospheric forcing and sea ice deformation have matching energetic scales at several hundred kilometers and timescales of days. An example of northerly winds during the April 1992 Arctic Leads Experiment period suggests discontinuous type behavior upwind of the Alaska coast followed by a general opening behavior with easterly winds. There appear to be natural scale divisions between climate scale sea ice processes of O(100-300 km) which resolve aggregate behavior, regional scale O(10-50 km) which is necessary to resolve observed shearing behavior, and the flee scale O(1 km). Because the climate scale is two levels removed from the flee scale, care must be exercised in using ice properties from the flee scale in climate scale models; ice strength is an example of such a scale dependent parameter.