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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)

  • topography tool (components/eam/tools/topo_tool/cube_to_target)

  • homme_tool  ( components/homme/test/tool, used to create SCRIP files).

Topography needs to be interpolated from a high resolution USGS file, and then doctored up a bit to allow the model to run stably with the new topography. The tool chain used to compute topography is documented in the following paper:  

P.H. Lauritzen, J.T. Bacmeister, P.F. Callaghan, M. Taylor,  NCAR_Topo (v1.0): NCAR global model topography generation software for unstructured grids, Geosci. Model Dev., 8, 3975-3986, 2015.

There are three main steps in this process:

Step (a) downsample USGS topography data to the atmosphere grid
Step (b) apply dycore-specific smoothing to reduce the amount of gravity wave noise if the topography is too rough. This is a tunable parameter, and a rigorous analysis probably needs to be performed to determine the optimal tuning parameter for future very-high-resolution atmosphere grids.  For physgrid configurations (pg1, pg2, pg3)t here is the extra step of generating consistent topo data on both the GLL (dynamics) and pgN (physics) grid. 
Step (c) based on the smoothed topography, compute the SGH and SGH30 surface roughness fields used by some parameterizations

Steps (a) and (c) use the topography tool located at components/eam/tools/topo_tool/cube_to_target in the E3SM repo, as well as homme_tool.

Step (b) requires running the homme_tool's smoothing algorithm.  The namelist should be edited to specify the resolution (NE value) or grid file (RRM) grid and the amount of smoothing
Detailed instructions depend on which version of the model is being used:

  • E3SM V1. V1 Topography: GLL grids

    • V1 uses topography on a GLL grid with a laplacing smoothing. The smoothing reduces the effective resolution of the topography from 2dx to 6.4dx. (effective resolution is determined by the first wavelength to be damped by 50% from the unsmoothed topography, computed via spherical harmonic spectra)

    • V1 only needs data on the GLL grid.

    • Tool chain: Requires cube_to_target, homme_tool, and a SCRIP file for the grid.

    • V1 has poor treatment of topography and compensates in part with increased divergence damping.

  • E3SM V2:V2 Topography: GLL/PG2 grids

    • V2 needs topography on the GLL grid, and then a consistent topography on the PG2 grid (created with the same GLL->PG2 algorithm used internally when running EAM)

    • V2 uses the same smoothing as V1: 50% damping of the 6.4dx wavelength.

    • V2 has improved topography treatment over V1. V2 configurations do not need to run with increased divergence damping.

  • E3SM V3: V3 Topography: GLL/PG2 grids

    • The (proposed) V3 tool chain is similar to V2, with minor modifications to in the smoothing algorithm.

    • V3 has further improved topography treatments over V2, supporting significantly rougher topography ( /wiki/spaces/NGDNA/pages/2411397876 )

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