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- sum of area weights is close to physical area
- mapping weights are between 0 and 1.
- For higher order maps, it may be acceptable for small overshoots, but we need to test this.
- FV2 map weights will violate this condition, but they are then corrected with CAAS.
- Consistency: Row sum of weights (measures what happens when mapping a constant function):
- Should be 1 to machine precision for all grids where a >= b. (global → regional)
- For grids with a<b (such as ocn→atm) row sums should be 1.0 at all ocean points, 0 at all land points, and between 0 and 1 at coastal points.
- Conservation: area_b weighted column sum of weights = area_a (exact for conservation, close otherwise)
- Should be equal to machine precision for all grids where a <= b. (regional → global)
- For grids with a>b (such as atm->ocn) should be equal to machine precision at all ocean points, 0 at all land points and between 0 and 1 at coastal points
- Non-conservative maps are expected to have small errors in the above metric. The traditional ESMF bilinear map does not include areas in the map file and this metric might not be accurate.
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There is a python package that can perform a more detailed analysis of mapping files used within a configured E3SM case: Map file analysis. It will create a PDF document with a page for each mapping file listing several metrics as which:
- lists weight, consistency and conservation metrics as well as their desired value and allowable variation.
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- For atmosphere target grids, check consistency with the atmosphere land fraction mask
- Measure mapping error using a standard test function, plotting the results and computing L2 and max errors. These errors can be compared to know working configurations to determine if they are sufficiently small.
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Older information from v1 and v2 development:
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