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Is sea ice modeling rocket science?

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SIPW05 - SIP Follow on: Mathematics of sea ice in the twenty-first century

In addition to simulating sea ice thermodynamic processes, a sea ice dynamical model is necessary for a realistic representation of the spatial distribution of ice thickness and concentration, and (solid) freshwater transport from the Arctic to the northern North Atlantic in for instance Global Climate Models. This can be accomplished by using any parameterizations of ice-ice interactions in the dynamical model that include some transition from low deformation to large deformation (or fracture) when critical internal ice stresses in shear and compression are reached. Of equal importance is a realistic simulation of sea ice deformation (shear and divergence) along the fracture lines, called Linear Kinematic Features (LKFs), where moisture, salt and heat between the surface ocean and the atmosphere are exchanged. LKFs are both intermittent in time and localized in space and conjugate pairs of fracture lines intersect over a specific range of angles. The source of this intermittency and localization however remains unknown: yet again, any model that considers a transition from low deformation to large deformation when critical internal stresses in shear and compression are reached reproduce these fractal properties (at the scale they are currently resolved). And while the angle between fracture lines follows theory for rheological models with a normal flow rule (alignment of stress and strain invariants axes), they no longer follow theory for models with a non-normal flow rule (appropriate for real sea ice) in simple uniaxial loading experiment nor in realistic pan-Arctic simulations irrespective of the rheological model used. The sensitivity of the spatial and temporal scaling to ad hoc parameterizations or poorly constrained parameters such as damage or shear and compressive strength, and the relative importance of ice-ice interactions compared to the first order balance of surface wind stress and water drag also point to a lack of understanding of first order processes governing sea ice deformations. All in all, current sea-ice dynamical models are sensitive to poorly constrained parameters and a better understanding of the questions posed above will be necessary before we can propose a rheological model that reproduces all key observed sea-ice features.   


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