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Grids

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Beau Cronin edited this page Jun 20, 2016 · 9 revisions

The grids are specified in CESM by setting an overall model resolution. Once the overall model resolution is set, components will read in appropriate grids files and the coupler will read in appropriate mapping weights files. Coupler mapping weights are always generated externally in CESM. The components will send the grid data to the coupler at initialization, and the coupler will check that the component grids are consistent with each other and with the mapping weights files.

In CESM1.2, the ocean and ice must be on the same grid, but the atmosphere and land and river runoff can each be on different grids. Each component determines its own unique grid decomposition based upon the total number of pes assigned to that component.

From here

There are several basic kinds of grid:

  • Finite Volume grids store the average value of a quantity or function within each zone
    • Example: f19 or 1.9x2.5 is 1.9 by 2.5 degrees, and is 144 (360 / 2.5) by 96 (180 / 1.9) cells
    • Used for: atmosphere, land
  • Global Spectral or Gaussian grids use (sums of) spherical harmonics, with the resolution determined by the number of basis functions included in the sum
    • Example: T85 is about 1.4 degrees, and is 128 cells in latitude by 256 cells in longitude
    • Common resolutions
  • Cubed Sphere or spectral element grids
    • Example: ne30np4 is a 1 degree cubed sphere, with 48,602 cells
    • Used for: atmosphere, land
  • Displaced Pole grids are finite volume grids where the pole has been moved under Greenland in order to keep that singularity out of the domain of the model
    • Example: gx3v7 is a 3 degree displaced pole, with 100 cells in latitude by 116 cells in longitude
    • Used for: ocean, sea ice

In CESM, there are complex rules governing which grids can be used together for different model components. While it is possible for the user to define a new grid combination, it's best to stick with a predefined setting. All existing grid settings are defined in config_grid.xml, and the same information is available in this web page.

Grid naming conventions

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