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, Stockholm University, Uppsala UniversityIce sheets, with connected ice shelves, are important components of the global climate system. Numerical models help us both in understanding past ice configurations (through paleoglacial simulations), and in predicting future ones. Ice can be regarded as a fluid with a very high viscosity, and governing its dynamics are the Stokes equations. Stress and strain-rate are related by a non-linear constitutive relation, the so-called Glen's flow law. In many large-scale ice sheet codes, and certainly in those employed to run paleo simulations, the governing equations are approximated in different manners in order to speed up simulations, the most common approximation being the so-called shallow ice approximation (SIA).
An ice sheet (the grounded part) deforms due to its own weight and flows out onto the sea, forming an ice shelf (the floating part). The ice can be either cold (with a temperature below the pressure melting point) or temperate (with an temperature at the pressure meltling point).
Models using the shallow ice approximation typically fail in modeling ice streams (narrow band of faster flowing ice) and the coupling between ice sheet and ice shelves. In this project a more accurate approximation, the second order shallow ice approximation (SO-SIA), is implemented in the ice sheet code SICOPOLIS in order to overcome these problems. The overall goal to develop an ice sheet model that can simulate coupled ice sheet/ice stream/ice shelf systems accurately and fast.
Computed surface velocities in the Greenland Ice Sheet, using the shallow ice approximation. In the north eastern part (at the red arrow) a large ice stream is missing.
To verify the model, benchmark experiments (ISMIP-HOM) are carried out, comparing the results with other models.
In benchmark experiments a simple ice sheet with a flat ice surface and sinusodial bedrock topography is modeled. This picture shows the pressure according to the second order shallow ice approximation.
Publications related to the project.
. Master's thesis by Josefin Ahlkrona, 2011. 8th of February, 2012: Workshop in Ice Modeling and Simulation
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