Difference between revisions of "Ice Sheet Evolution Experiments"

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Now that we've (1) convinced ourselves that the higher-order model is "working" (at least as well as other higher-order models out there) and (2) added some code so that we can evolve the ice sheet geometry, we can do some simple experiments looking at the combination of the two. By "simple", I mean coarse resolution, idealized domains with idealized boundary conditions. These may actually be somewhat "non-sensicle" with respect to real ice sheets, but that makes the output much more easy to analyze.
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Now that we've (1) convinced ourselves that the higher-order model is "working" (at least as well as other higher-order models out there) and (2) added some code so that we can evolve the ice sheet geometry, we can do some simple experiments looking at the combination of the two. By "simple", I mean coarse resolution, idealized domains with idealized boundary conditions. These may actually be somewhat "non-sensicle" with respect to real ice sheets, but they are still useful exercises for illustrating other important issues.
  
  
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* Allow a parablic-shaped mound of ice to spread out under it's own weight. The non-sensicle part is that we will assume (i) zero surface mass balance (no accumulation or ablation) and (ii) a fixed lateral boundary. That is, the ice sheet margin won't be allowed to move past it's original position (think of an ice sheet surrounded by a very tall (and very strong) fence - the ice sheet will eventually take on the shape of a disk with uniform thickness).
 
* Allow a parablic-shaped mound of ice to spread out under it's own weight. The non-sensicle part is that we will assume (i) zero surface mass balance (no accumulation or ablation) and (ii) a fixed lateral boundary. That is, the ice sheet margin won't be allowed to move past it's original position (think of an ice sheet surrounded by a very tall (and very strong) fence - the ice sheet will eventually take on the shape of a disk with uniform thickness).
  
* Evolve a confined ice shelf of uniform thickness and temperature for XX years (that is, we will evolve the diagnostic solution to the unpublished ESIMINT ice shelf experiments 3 and 4 [http://homepages.vub.ac.be/~phuybrec/eismint/iceshelf.html], which you [[COMSOL activities#Shallow shelf approximation|explored a bit earlier in one of the COMSOL exercises]]. The non-sensicle part here is that again, we assume no accumulation or ablation. Thus, the only thing that can happen is that ice flows out of the shelf front. Eventually, the shelf should thin to zero thickness (but how and when that happens will vary depending on a number of things).
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* Evolve a confined ice shelf of uniform thickness and temperature. That is, we will evolve the diagnostic solution to the unpublished ESIMINT ice shelf experiments 3 and 4 [http://homepages.vub.ac.be/~phuybrec/eismint/iceshelf.html], which you [[COMSOL activities#Shallow shelf approximation|explored a bit earlier in one of the COMSOL exercises]]. The non-sensicle part here is that again, we assume no accumulation or ablation. Thus, the only thing that can happen is that ice flows out of the shelf front. Eventually, the shelf should thin to zero thickness (but how and when that happens will vary depending on a number of things).
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== Experiment 1: evolve the blob ==
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Change your current directory to '''tests/ho-other''' (i.e. higher-order other). There will be a model configuration file there called '''blob.config''' and a related python scrip '''blob.py''' for making the input netCDF files (both courtesy of Tim Bocek).
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== Experiment 2: evolve the shelf ==
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Change your current directory to '''tests/shelf/'''. There will be a model configuration file there called '''confined-shelf.config''' and a related python scrip '''confined-shelf.py''' for making the input netCDF files (again, both courtesy of Tim Bocek).
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Increase/decrease this time by changing rate factor.
 
Increase/decrease this time by changing rate factor.
 
Can we compare the profile at some time w/ that from SIA model and figure out why/where differences exist?
 
Can we compare the profile at some time w/ that from SIA model and figure out why/where differences exist?
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Can we compare profile from upwinding scheme w/ profile from remapping scheme?
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How close can we get to the CFL limit and still get stable evolution for a XX year run?

Revision as of 13:58, 6 August 2009

Now that we've (1) convinced ourselves that the higher-order model is "working" (at least as well as other higher-order models out there) and (2) added some code so that we can evolve the ice sheet geometry, we can do some simple experiments looking at the combination of the two. By "simple", I mean coarse resolution, idealized domains with idealized boundary conditions. These may actually be somewhat "non-sensicle" with respect to real ice sheets, but they are still useful exercises for illustrating other important issues.


The two experiments we will attempt are:

  • Allow a parablic-shaped mound of ice to spread out under it's own weight. The non-sensicle part is that we will assume (i) zero surface mass balance (no accumulation or ablation) and (ii) a fixed lateral boundary. That is, the ice sheet margin won't be allowed to move past it's original position (think of an ice sheet surrounded by a very tall (and very strong) fence - the ice sheet will eventually take on the shape of a disk with uniform thickness).
  • Evolve a confined ice shelf of uniform thickness and temperature. That is, we will evolve the diagnostic solution to the unpublished ESIMINT ice shelf experiments 3 and 4 [1], which you explored a bit earlier in one of the COMSOL exercises. The non-sensicle part here is that again, we assume no accumulation or ablation. Thus, the only thing that can happen is that ice flows out of the shelf front. Eventually, the shelf should thin to zero thickness (but how and when that happens will vary depending on a number of things).


Experiment 1: evolve the blob

Change your current directory to tests/ho-other (i.e. higher-order other). There will be a model configuration file there called blob.config and a related python scrip blob.py for making the input netCDF files (both courtesy of Tim Bocek).


Experiment 2: evolve the shelf

Change your current directory to tests/shelf/. There will be a model configuration file there called confined-shelf.config and a related python scrip confined-shelf.py for making the input netCDF files (again, both courtesy of Tim Bocek).



Questions

Shelf: what happens if you change the rate factor by an order of mag in the python script? Decrease it ... increase it (w/o altering time step, should lead to crash due to CFL violation - use this as an excuse to alter subroutine and add CFL warning) Change thickness by factor of 2? Look at rate of decay of thickness and estimate how long until shelf-front thins to zero Discuss problem w/ domain edges - thickness stays at 500m forever, which is non-physical and due to BCs (only "inside" of domain acts in a way we'd expect)

Blob: How long to decay to disk? Increase/decrease this time by changing rate factor. Can we compare the profile at some time w/ that from SIA model and figure out why/where differences exist? Can we compare profile from upwinding scheme w/ profile from remapping scheme? How close can we get to the CFL limit and still get stable evolution for a XX year run?