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

and what is observed becomes less important.
on free drift:
currents were dominant.
This is much like our comment
that errors in the air stress were less important when ocean
In the present case we have the same contribution
from ocean currents and one other important one as well, from ice stress
divergence.
Now that we have evaluated the effect of air stress errors on ice velocity,
we take a closer look at certain second-order quantities, such as stretching
and stress.
In Figures 10-12 we present the stretching tensor field during the three
days we have simulated using the predicted air stress fields.
In all cases
there is general agreement; that is, when no deformation is occurring (as for
27 January), the same condition exists in the 24-, 36-, and 48-hour predic-
tions.
In fact, during this day all four plots are nearly the same. Only
small differences exist near the northwest boundary where the greatest
stretching occurs.
There the baseline stretching shows a maximum of about
3% per day uniaxial opening, while the predictions all show a maximum of about
2%.
In Figure 11, for 30 January, we see the same general pattern of large
shear in a narrow band off the North Slope, with uniaxial opening near Banks
Island.
In this case, however, there is a difference between magnitudes and
locations of the maxima.
the development of a narrow band of shear.
For example, the 24- and 36-hour predictions show
Pritchard et al. (1977) have
identified it as a flaw lead beginning near Barrow, running east, and curving
north to Banks Island; it can be identified readily in NOAA-4 satellite images
(Pritchard et al., 1977, Figs. 5-8).
cell widths) north of the observed region.
The feature is located about 80 km (two
the eastward part of the region is at rest and not moving as in the baseline
calculation.
Thus, the maximum uniaxial opening occurs about 200 km from
Banks Island rather than at the shore, as shown in Figure 9.
We should point
out, however, that the data buoy tracks (Pritchard et al., 1977) show the ice
in this region to be at rest. A look at Figure lld shows that the 48-hour
prediction is quite similar to the observed motions.
Furthermore, as we saw in Figure 8,
The baseline and all predicted stretching fields for 2 February (Fig. 12)
are similar to each other. Differences are on the order of 1% per day.
This
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