Write DZDXF/DZDYF derived from ZSF - #6
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CFBM reads the terrain gradients from the input file. Both gradients are derived form the reprojected ZSF. Sencil follows geogrid's calc_dfdz/calc_dfdy with centred difference in the interior, one-sided at the edges. Behavior unchanged for NFUEL_CAT and ZSF. Portions drafted with Claude Opus 5. Closes #5
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Thank you @masih-e! Can you confirm that you tested the new code and checked the output? |
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Closes #5
Derives
DZDXF/DZDYFfrom the reprojectedZSFand writes them alongsideNFUEL_CAT/ZSF.Boundary handling. The issue specifies "equivalent to extending terrain at
the edge." I used a one-sided difference instead. Replicating the edge into a
ghost cell leaves the numerator
z1-z0over a denominator of2h, whichreports half the true gradient, an O(1) error.
Map factor sense. Applied map factors, but multiplying where
calc_dfdx(WPS) divides. WRFmeasures grid spacing in projection space and treats the true inter-point
distance as
dx/MAPFAC—dyn_em/module_diffusion_em.F:1894builds itsphysical mixing length as
sqrt(dx/msftx * dy/msfty). So a physical gradientmultiplies by the map factor, and dividing doubles the error rather than
removing it. This reads like a WPS bug rather than a convention to match, but
flagging it since anyone diffing against a geogrid-produced file will see the
difference. Negligible at fire scale (5e-6 across the 40 km CT2 nest), 1.3%
across 2000 km, 8% across a continental domain.