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For an overview of the Topography generation process, see the parent page: Adding support for new grids

Requirements:

  • High resolution USGS topography file named USGS-topo-cube3000.nc (located in the CESM inputdata server here; note this is on a 3 km cubed sphere grid)
  • SCRIP-format atmosphere grid file
  • topography tool (components/cam/tools/topo_tool/cube_to_target)
  • homme_tool  (same tool used to create SCRIP files described above).tool  

For "pg2" grids (E3SM v2):  dont follow this page and instead see the instructions on  Special Considerations for FV Physics Grids 

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The unsmoothed topography then needs to be smoothed using the smoothing operator in HOMME. This is done using the homme_tool utility.  Follow the instructions above in the Adding support for new grids page, SCRIP section, to configure and build this tool.  A sample namelist for the topo smoothing option is given in components/homme/test/tool/toposmooth_gll.nl

  1. For cubed sphere grids:
    1. Set resolution via set ne = 4  (for ne4 example here).
    2. Set  smooth_phis_numcycle=16.    (adjustable paramemter, lower for less smoothing)
    3. Set smooth_phis_nudt.  This is a resolution dependent parameter, recommend value for cubed sphere grids is 28e7 * ( 30/NE)**2
  2. For RRM grids, we use the tensor laplace operator so that the amount of smoothing is proportional to the resolution
    1. ne=0, mesh_file=/path/to/exodus-rrm-grid-file.g
    2. Set  smooth_phis_numcycle=12.    (adjustable paramemter, lower for less smoothing)
    3. smooth_phis_nudt = 4e-16.  
  3. Set infilenames=/path/to/unsmoothed/PHISdata

After running the tool, the output will be named "geos", in the file phis-smoothed1.nc, along with other unnecessary fields.  To convert this file into an EAM topo file:

Step (c)

The topography tool then needs to be re-ran to compute the subgrid surface roughness. This is done by passing an extra argument to the topography tool with the smoothed topography output from the standalone HOMME run above:

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