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Often map file algorithm choices dont have much of an impact on the solution, but occasionally they do. Here is a great example showing the noise that can be generated when an aave map is used for upscaling coarse-to-fine mapping of a non-flux variables: /wiki/spaces/ECG/pages/2350776353
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For ESMF maps, we previously recommend bilinear maps for upscaling coarse-to-fine and aave for downscalingfine-to-coarse. All the TempestRemap algorithms recommended here should work well for either upscaling or downscalingcoarse-to-fine or fine-to-coarse.
- SE → Lat/Lon: "intbilin"
- "intbilin" if exact conservation is not needed.
- "mono" if exact conservation is needed and 1st order accurate is ok (i.e. for downscalingfine-to-coarse maps).
- Lat/Lon → SE
- FV→SE "mono". Disabling the conservation constraint with --noconserve does not improve accuracy
- SE → SE
- SE→SE "mono"
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- Some compsets use ESMF bilinear maps for state variables The bilinear algorithm introduces aliasing artifacts when mapping from a high-resolution to low-resolution region (downscaling). Some v1 compsets already use TR high-order for atm2ocn maps, which avoid this issue.
- We currently use ESMF conservative maps for fluxes. This algorithm uses piecewise-constant finite volume reconstruction. These maps are good for downscalingfine-to-coarse mapping, but will produce blocky artifacts when upscaling.
- ESMF conservative maps for spectral element grids requires us to first generate a "dual grid" that puts a finite volume around each spectral element node. Constructing this dual grid requires running a Matlab tool that uses Newton iteration to find the dual grid. For a high-resolution grid, this procedure can take several days. (For information on the dual grid, see SE Atmosphere Grid Overview (EAM & CAM)). The dual grid is contained in the SCRIP format metadata file.
- TR algorithms natively support finite element grids, do not require the SCRIP dual grid, and give more accurate results when remapping to/from a spectral element atmosphere grid.
- TR algorithm recommended for state variables is automatically downscalingcell integration based, so can always be used when mapping from high-res to low-res grids.
- Inline mapping: TempestRemap algorithms are part of the MOAB coupler, making it possible to eliminate mapping files and have them computed as needed.
- Land/Ocean Mask consistency: The flux ocn2atm map is used to define the land/ocean mask on the atmosphere grid. All other ocn2atm maps (state and vectors) must have the same range as the map uses for fluxes. That is, if a point on the atmosphere grid receives ocean data from the flux map, it must also receive ocean data from all other maps. The aave and bilinear maps do not have the same range, and thus if an aave map is used for fluxes, it must be used for all other ocn2atm maps. We speculate that TR maps all have the same range and thus we can use high order maps for ocn2atm state and vectors.
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