...
There was much discussion about how to handle topography with the new physgrid. The dynamics requires a smoothed topography on the GLL grid, but the physics parameterization for turbulent mountain stress operates on the physics grid, so the initial question was which grid should the input topography be on? PR's #3267 and #3406 introduced a new file format for topography and related tools that allow a better consistency between the representation of topography on both grids. Specifically, there are two new tools to support this new treatment of topography for the physgrid.
The tools are motivated by the following considerations: Both the dycore and the physics parameterizations require surface geopotential (topography) phi_s. Thus, there a number of requirements.
- The dycore needs these data at GLL points, and the physics needs them at FV cell centers.
- We require that the map of the GLL phi_s data be equal to the FV phi_s data.
- We want to run HOMME's smoother on GLL phi_s.
- We do not want to use the GLL dual grid, which requires using an unscalable tool; we want to use only the FV dual grid, which can be created using, e.g., TempestRemap in a matter of seconds.
To fulfill these requirements, we introduce a new topography file format that has all data at FV points and, in addition, phi_s at the GLL points.
The first tool is a simple converter, for convenience. The input is an old GLL topography file. The output is a topography file in the new GLL-physgrid format. SGH, SGH30, LANDFRAC, and LANDM_COSLAT are not quite as good as with second tool, but this converter works in one step:
...