1 Spatial Modelling of the Terrestrial Environment - Georeferencial

Modelling Ice Sheet Dynamics by Satellite-Derived Topography 27
-65 o
-50 o
-35 o
-20 o
-5 o
80 o
75 o
70 o
65 o
-50 o
0 500 km
60 o
a
Figure 2.8 (a) Contour plot of balance velocities estimated for the Greenland ice sheet, and
(b) the same as (a) but for the Antarctic ice sheet. The contour intervals plotted are 25, 50,
100, 200, 300 and 500 m a −1 .
moving from simulation 1 to 4. The simplest configuration was for simulation 1, where
the ice was assumed to be isothermal and there was no basal sliding. This means that
the thermodynamic component had been switched off and the ice viscosity had a constant
value with depth. This is a gross simplification and known to be a poor representation of the
englacial dynamics. In reality, most of the ice deformation takes place in the bottom 10%
of the column as the ice is warmest here and subject to the highest stress. The difference in
viscosity of ice between the surface and bed can be as much as 10 3 . It might be expected,
therefore, that this most basic simulation, lacking two crucial physical processes, would
provide the poorest agreement with U b .
In the isothermal cases (experiments 1 and 2) U d generally decreases with respect to
U b moving from the centre towards the margins. This means the ice is too stiff inland and