Difference between revisions of "ISMIP-HOM test suite exercise"

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== Background ==
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In this exercise, we will test out Glimmer/CISM's higher-order stress balance subroutines by running the model through a few of the [http://homepages.ulb.ac.be/~fpattyn/ismip/ ISMIP-HOM] test suite problems. The tests we'll run are for 3d models, so the domain and boundary conditions vary in the ''x'' and ''y'' directions (i.e. in map plane). For test A, the topography varies periodically in ''x'' and ''y'', and for test C, the basal traction varies periodically in ''x'' and ''y''. While the amplitude of the variations is the same for all tests, the wavelength is decreased by a factor of two for each successive test. For λ=160 km, the velocities solutions essentially look like that from a shallow ice model. Halving λ to 80 km, then to 40, 20, 10, and finally 5 km, the higher-order components of the stress balance become successively more important to the velocity solution.  Figures 1 and 2 below shows relevant input data for each of the two experiments for λ = 80km. Here, in the interest of time, we will only run tests for the first three wavelengths in the series (160, 80, and 40 km).
 
In this exercise, we will test out Glimmer/CISM's higher-order stress balance subroutines by running the model through a few of the [http://homepages.ulb.ac.be/~fpattyn/ismip/ ISMIP-HOM] test suite problems. The tests we'll run are for 3d models, so the domain and boundary conditions vary in the ''x'' and ''y'' directions (i.e. in map plane). For test A, the topography varies periodically in ''x'' and ''y'', and for test C, the basal traction varies periodically in ''x'' and ''y''. While the amplitude of the variations is the same for all tests, the wavelength is decreased by a factor of two for each successive test. For λ=160 km, the velocities solutions essentially look like that from a shallow ice model. Halving λ to 80 km, then to 40, 20, 10, and finally 5 km, the higher-order components of the stress balance become successively more important to the velocity solution.  Figures 1 and 2 below shows relevant input data for each of the two experiments for λ = 80km. Here, in the interest of time, we will only run tests for the first three wavelengths in the series (160, 80, and 40 km).
  

Revision as of 10:31, 3 August 2009

Background

In this exercise, we will test out Glimmer/CISM's higher-order stress balance subroutines by running the model through a few of the ISMIP-HOM test suite problems. The tests we'll run are for 3d models, so the domain and boundary conditions vary in the x and y directions (i.e. in map plane). For test A, the topography varies periodically in x and y, and for test C, the basal traction varies periodically in x and y. While the amplitude of the variations is the same for all tests, the wavelength is decreased by a factor of two for each successive test. For λ=160 km, the velocities solutions essentially look like that from a shallow ice model. Halving λ to 80 km, then to 40, 20, 10, and finally 5 km, the higher-order components of the stress balance become successively more important to the velocity solution. Figures 1 and 2 below shows relevant input data for each of the two experiments for λ = 80km. Here, in the interest of time, we will only run tests for the first three wavelengths in the series (160, 80, and 40 km).


Figure 1: ISMIP-HOM test A input (periodic basal roughness with no sliding); ice thickness, basal topography, and surface elevation. The basal boundary condition is no slip and the lateral boundary conditions are periodic velocities in x and y.

Ismiphom.a.jpg


Figure 2: ISMIP-HOM test C input (sliding according to periodic basal traction); ice thickness,bBetasquared, and surface elevation. Sliding takes place along the basal boundary according to a "betasquared" (traction) type sliding law. The lateral boundary conditions are periodic velocities in x and y.

Ismiphom.c.jpg


To set up the experiments, we will use some configuration files and python scripts developed by Tim Bocek and Jesse Johnson. These set the correct flags, so that Glimmer/CISM calls the necessary subroutines, and construct the necessary input netCDF files.

First, we need to change into the correct directory where the test scripts and configuration files live. Assuming that you are starting in the directory

glimmer/src/fortran/

you will need to type

cd ../tests/ISMIP-HOM/




Have them play w/ the grid spacing to see how that affects results?

Can we get a 0-order solution for these as well?