CAM-SE works with data stored at Gauss-Lobatto-Legendre (GLL) nodes. These nodes can be interpreted in several ways shown in the three grids below. In all three grids, the GLL nodes are the same (the green dots in the figure). Internally, the dycore uses the CAM-SE native grid connectivity, but the rest of CAM and ACME has no knowledge of the grid connectivity and only sees data at GLL nodes and their associated area weight. The other other types of connectivity are not used within the model, but are sometimes used by pre- and post-processing tools.
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- <grid>_latlon_<date>.nc
- This file contains the GLL node locations and the native grid and the subcell grid connectivity
- Used by CAM's interpic_new to generate initial condition files
- Used by Paraview and Visit to plot native grid CAM-SE output
- Used by TempestRemap to create mapping files (when specifying the Jacobian to override Tempests internal reference element map)
- <grid>_scrip_<date.nc>
- This file contains the GLL node locations, the dual grid cell vertices and the dual grid connectivity
- Used by ESMF to create mapping files.
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- For quasi-uniform cubed-sphere grids, ACME currently uses the "pentagons" option to construct the dual grid for making ESMF mapping files. To create these meta data grid files, we use a utility distributed with the ACME code - see acme/components/homme/test/templates.
- For RRM grids, ACME currently uses the "cheveron" option to construct the dual grid for making ESMF mapping files. To create these meta data grid files we use a Matlab program that performs a Newton interation. This matlab code is in the ACME PreAndPostProcessingScripts repo under regridding/spectral_elements_grid_utilities/
Future Plans
We note that the TempestRemap package uses an algorithm that understands both SE and FV grids (Ullrich & Taylor, MWR 2015) and can produce map files directly from the CAM-SE Native grid. It only needs the SE Native grid (the first grid shown on this page) and does not need any type of dual grid. These mapping files are more accurate since they take advantage of the SE discretization. If ACME atmosphere adopted TempestRemap mapping files, we will not need to use the SE dual grid.
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