Multi-scales in sea ice: A review of sea ice structure and how it relates to mechanics
J. Hutchings, S. Durski, A. Khosravi
Oregon State University
Sea ice growth history defines its structure in the vertical, with spatial scales defined by the crystal structure, grain boundaries, voids and brine channels. Most strength testing is on cm to sub-meter scale, and the bulk strength is, while not fully characterized, reasonably well understood. There is evidence for scale invariance of the material properties of sea ice over scales of centimeters to 100m. At the scale seas within the Arctic basin, we see similar mechanisms for failure as in the laboratory with Coulombic rheological behavior. However between these scales the sea ice deformation is not scale invariant. Suggesting different physical properties or forcing conditions for pack ice between kilometer to 10s of kilometers scales. Considering the structure of pack ice we describe a multiscale hierarchical structure of pack ice that might explain this. In particular the deformation in kilometer to 10 kilometer regime is controlled by floe interaction and development of shear bands. These have very different boundaries forcing motion than on the largest scale where synoptic wind patterns drive ice to interact with the coast. In both situations the scale of deformation is set by the size of the domain between these differing boundaries. The load on the ice is likely to have different spectral character between the two situations due to the different wind fetch and the role of ice interaction. Implications for modeling are that the different methods should be taken to build empirical constitutive relationships for each scale. Bridging between scales to upscale measurable ice strength, on scales of cm to 100m, to pack ice, requires consideration of the changing structure of the ice between these scales. It can not be expected a sheet of intact ice will behave the same way as a cracked sheet of ice or an aggregate of loose or cemented floes / consolidated ridges. The emergent scales based on ice structure are described, including those for which stress might be isotropic and homogeneously distributed.
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