Author(s): Yoshiki Kawano; Tetsuya Ohashi
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Abstract: Developments of sea ice polycrystals from the sea surface are simulated under two-dimensional approximation by combining numerical models for crystal growth, salinity diffusion and flux of heat. Anisotropic growth of ice crystals from a number of nuclei and their mutual impingements are numerically reproduced by a simple and novel technique, named Voronoi dynamics. In an extreme case where the growth rate is isotropic and the initial salinity is zero, resultant microstructure consists of Voronoi polyhedron. Discharge of salt from solidified region and salinity condensation at the solid-liquid interface are also taken into the simulation. Diffusion process of salinity and heat flux are evaluated by solving equations for diffusion and heat conduction, and growth of ice crystals is affected by these two factors. Results show that layer of granular grains are formed near the sea surface and columnar shaped grains develop below it. Brine regions are mainly formed along grain boundaries in the layer of granular grains, while in the region of columnar shaped grains, brine regions exist both along grain boundaries and inside grains. Columnar shaped crystal grains consist of ice platelets growing in the vertical direction and brine layers are sandwiched between them. Mechanism for the formation of this substructure, ice platelets and brine layers is discussed in terms of Mullins-Sekerka type instability of solid-liquid interface and temperature gradient due to cooling from sea surface. These microstructural features are in accordance with experimental observations.
Year: 2008