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NCL: HOMME: High-Order Multiscale Modeling Environment model (formerly SEAM)

Non-uniform grids and triangular mesh conversion

The HOMME grid a non-uniform grid. The data may be plotted directly (no explicit interpolation to another grid required) by using the triangular mesh. This is the default if the array to be plotted is one dimensional and the lat/lon information is provided by setting the sfXArray and sfYArray resources.

For more information on non-uniform grids that NCL can handle, see the document "Non-uniform grids that NCL can contour."

homme_1.ncl: This example shows how to create a basic filled contour plot of a SEAM grid over a cylindrical equidistant map.
homme_2.ncl: This example creates a basic color filled contour plot of a HOMME grid over a cylindrical equidistant map. No explicit interpolation to another grid is performed. Setting the sfXArray and sfYArray resources and using the original HOMME data invokes the triangular mesh option.
ESMF_regrid_18.ncl: This example, taken from the ESMF Regridding page, shows how to regrid two variables (PSL and T) on a HOMME unstructured finite volume grid (48602 cells) to a 96 x 144 finite volume (FV) rectilinear grid.

Once the first variable is regridded using ESMF_regrid and the weights file has been generated, the second variable can be regridded using ESMF_regrid_with_weights with this weights file.

ESMF_regrid_19.ncl: This is another example from the ESMF Regridding page. It shows how to regrid data on a HOMME unstructured grid to POP curvilinear gx1v3 grid (384 x 320).

In this case, the POP grid was retrieved from an old weights file from a previous regridding that went from a 1x1 degree grid to a POP grid.

The destination lat/lon arrays on this weights file have corresponding names "yc_b" and "xc_b", and are one-dimensional. You have to reshape these 1D arrays to their original 2D structure using the "dst_grid_dims" variable on the file. The POP weights file also contains a mask grid called "mask_b" that you must apply via the special "DstMask2D" option.