Page Comparison

See also CAM-FV Grid Overview

CAM-SE works with data stored at Gauss-Lobatto-Legendre (GLL) nodes.  These nodes can be interpreted in several ways shown in various grids below.  In the "SE native grid", "SE subcell grid" and "SE dual grid", 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 E3SM 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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Meta data files:  (not used directly by the E3SM model, but used by the various pre- and post-processing utilities

• Exodus:  <grid>.g
  • NetCDF file with grid information in the Exodus format:   https://github.com/gsjaardema/seacas#exodus
  • This file contains a description of the spectral elements, but not the GLL or PG cells within each spectral element. 
  • Can be used by TempestRemap to make mapping files for GLL grids for a given np. 
  • Can be used by TempestRemap to make SCRIP files for PG grids.  
• "latlon":   <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
• SCRIP:  <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.  

Tools:

1. TempestRemap:  https://github.com/ClimateGlobalChange/tempestremap.   
   1. Used to make Exodus files (GLL and physgrid) and to make SCRIP files (physgrid only).
   2. Used to make mapping files for GLL grids directly from the Exodus file.
2. Obsolete:  For quasi-uniform cubed-sphere grids, E3SM 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 E3SM code - see e3sm/components/homme/test/tool.
3. Obsolete:  For RRM grids, E3SM v1 used 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 E3SM PreAndPostProcessingScripts repo under regridding/spectral_elements_grid_utilities/

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Using TempestRemap to create Exodus and SCRIP files: 

1. To create the Exodus file.  For cubed sphere grids with a resolution of "NE":  
   1. GenerateCSMesh --alt --res $NE --file ne${NE}.g
   2. For RRM grids, the Exodus .g file is part of the model configuration and is stored along with the initial condition files in the E3SM input data server, inputdata/atm/cam/inic/homme
2. To create a SCRIP file for PG2 grids from the Exodus file:
   1. GenerateVolumetricMesh --in ne${NE}.g --out ne${NE}pg2.g --np 2 --uniform 2
   2. ConvertExodusToSCRIP --in ne${NE}pg2.g  --out ne${NE}pg2.scrip.nc
3. For E3SM V2, the physics is running on the "PG2" grid.  This means most output, and all coupled model mapping files need to work with PG2 grids.   
   1. Mapping files should be created using the SCRIP file