other is how to link it to actual opening, which depends on ice condition such as geometric pattern of leads and cracks. The first problem is essentially statistical. That is how to estimate the deformation field in a robust way. Previous experience shows that the deformation field is much more sensitive to a smoothing and interpolation schemes than the velocity field, At present, an effort is put into estimating deformation characteristics such as divergence, pure shear, and the direction of principal shear. An early indication is that it is more robust to compute the deformation field by averaging deformation characteristics directly, rather than based on an averaged and interpolated velocity field and differentiate it. It also makes more sense to take this route as the ice velocity field and associated deformation field have significant variability in a short time scale (less than a synoptic scale). It seems necessary to compile the deformation field as a cumulative map with an incremental time scale short enough to capture high frequency variability. In essence, the second problem can be paraphrased as what is the functional relationship between deformation characteristics and the amount of opening? Although there is some uncertainty associated with an exact role by pure shear motion in the opening, enough progress has been made recently [Stern et al.,.1995], in fact, we are now compiling buoy data to construct maps of daily deformation fields. On the basis of them, we are further computing some statistics of the opening, such as a maximum amount of opening. This would ultimately help us to understand the role of leads and cracks in air-sea-ice interactions.
4 Remarks
In this presentation, two areas where the mechanical property of sea ice interacts with the dense water formation are discussed, the influence of ice mechanical property on the dense water formation in coastal and interior regions of the Arctic Ocean. The fundamental question is how much of the open water appears as a consequence of deformation in the ice field. Over the coastal region, the mechanical property measured by a new index for brittleness gives information as to lead and/or polynya characteristics. For the interior region, the combination of, perhaps, a daily deformation map and a functional estimate linking deformation characteristics to the amount of opening would provide us with means to estimate the aerial average salt flux. It seems that we now have machinery to relate the mechanical property of ice directly to the formation of the dense water. It remains to be seen that a further assimilation of satellite remote sensed and buoy data would allow us to make a real progress in this area near future.
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