Summary of Suckale et al. paper
Basic physics
Meltwater produced in the partially molten shear margin forms channelized
drainage system, which brings down the shear stress.
Some important points
Steady state
Given the growth rate of the Dragon margin, it may not be very conclusive to
say the margin is in a steady state. It is necessary to check the relaxation time
scale of the stream margin and compare it with the time span of the model
Parameter mapping
In the model the enhancement value E is set to 1 to reduce the ambiguity. The
value E is not a physical variable by itself, but represents effects of grain size,
impurities, fabrics and possibly other variables, and it is difficult to constrain it
from first principles. By introducing E, you increase the degrees of freedom of
the model, and by manipulating E you can match any data by tweaking these
not-so-well-grounded parameters (“I can make a rabbit out of it”, said Jenny).
Ice rheology
The ice rheology is a combined mechanism of diffusional creep ‘D and Glen’s
law ‘G. It is shown in the paper that the Glen’s law dominates the ice rheology
in the high-stress region around the crack tip. It is not clear whether similar
results can obtained if a different rheology, e.g. rheology proposed by Goldsby, is
used.
Benchmark test
Figure 5 shows the benchmark test for Dragon margin. It shows that the far-field
dominates the overall behavior, and the singularity is only important at the
very immediate vicinity. For very wide ice streams, the numerical model has no
discernible difference with the analytical solution.
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