AIDJEX Bulletin #40 - Polar Science Center - University of Washington

condition is similar in magnitude to 27 January, when the major portion of
the region was not deforming.
In summary, we find that the deformation field is approximated equally
well by all predictions, and there is good qualitative agreement with the
stretching. It is extremely important to represent the deformation field
well, since it is the stretching tensor that causes mechanical redistribution
of the ice state. In the present simulations we have ignored the thickness
distribution for reasons explained in Pritchard et al. (1977). However, it
remains important to approximate the deformations even when a perfectly plastic
model is used; otherwise, we would expect significant changes in the solution
when the thickness distribution is included and the yield strength is determined
as a function of the thickness distribution. This statement is not true in
all cases, but it is true in the present conditions, where changes in yield
strength would not have a dominant effect on changing the solution.
In Figures 13-15 a stress tensor field is simulated for the three days of
interest. All information contained in the stress tensors at each point is
presented. Principal values are shown proportional to line length in the
direction given, so that we are able to identify both principal values and
direction in these field plots. It should be noted that the stress tensor
is quite dependent on details of the deformation field and can be extremely
sensitive to certain errors. By the same token, since the stress is constrained
to lie within or on the yield surface, the amount of error that can be introduced
to the stress state has a certain maximum. From these two conflicting
ideas we are uncertain how sensitive the stress field will be to the errors
in driving force.
It is seen that the magnitude of the principal values and variations
across the field are in general agreement in all cases, a result caused by
the bound introduced by the yield surface. The comparison when the material
is at rest on 27 January and 2 February is quite close. There seems to be no
degradation in any case as prediction times go from 24 to 48 hours. For 30
January the baseline response appears appreciably different on the western
edge from all three predicted values. It is possible that our errors in the
baseline air stress have again caused this deviation. We make this conjecture
primarily because the three predicted fields shown in Figure 14 are so similar.
In any case, in the nearshore regions of the Alaskan continental shelf the
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