1/8 Fix dual-regional ESMF weight generation - #38
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Use ESMF_RegridWeightGen’s -r option consistently when both source and
destination grids are regional, replacing contradictory combinations of
-r, --src_regional, and --dest_regional. Apply the correction to
ERA5-to-satellite, land-cover-to-satellite, and satellite-to-WRF weight
generation, and add regression tests that capture each generated command
before ESMF executes.
Treat ESMF regridding grids as regional
Use ESMF_RegridWeightGen’s -r option alone when both source and
destination grids are regional so regional source and destination grids
are not interpreted as periodic global grids. This prevents invalid
connections across a regional grid’s opposing boundaries. Without this,
regrids can fail obviously near the 180th meridian, and quite possibly
fail subtly for some grids in other parts of world.
The ESMF_RegridWeightGen reference manual defines -r as the
dual-regional case; --src_regional instead means a regional source with
a global destination, while --dst_regional means a global source with a
regional destination. Remove the contradictory mixed-grid flags from the
generic ESMF and fractional land-cover command builders so regional
MODIS and ancillary- grid boundaries are handled according to the ESMF
documented interface.
from ESMF_RegridWeightGen docs:
-r - an optional argument specifying that the source and
destination grids are regional grids. If the argument
is not given, the grids are assumed to be global.
--src_regional - an optional argument specifying that the source is
a regional grid and the destination is a global grid.
--dst_regional - an optional argument specifying that the destination
is a regional grid and the source is a global grid.
Test dual-regional ESMF commands
Add regression coverage for ESMF_RegridWeightGen command construction in
WRF-output and fractional land-cover regridding paths. Mock external
execution while asserting that two regional grids use -r alone, omit the
contradictory one-sided regional flags, and retain the land-cover
unmapped-cell option.
Test ERA5 regional ESMF command
Add regression coverage for ERA5-to-satellite weight generation, which
is also affected by the dual-regional ESMF fix. The test constructs a
minimal meteorology handler, captures its generated command before ESMF
executes, and verifies that it uses -r alone rather than contradictory
per-grid regional flags.
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Fix dual-regional ESMF weight generation
Summary
ESMF_RegridWeightGendistinguishes between a source-only regional grid, a destination-only regional grid, and the case where both grids are regional. Several pyVPRM command builders used a contradictory combination of these options. This PR uses ESMF's dual-regional-roption consistently when both source and destination grids are regional.The correction applies to:
Why
The previous commands combined
-rwith source- and destination-specific regional flags. In theESMF_RegridWeightGencommand-line interface,--src_regionalmeans source regional AND destination global, while--dst_regionalmeans destination regional AND source global;-ris the option for both grids regional. Passing both--src_regionaland--dst_regionalis therefore contradictory.Treating both grids as regional is required for these pyVPRM workflows and prevents ESMF from applying global-grid topology assumptions. The documented options are listed in the ESMF_RegridWeightGen reference manual.
Validation
execution for the ERA5, land-cover, and WRF paths.
-rand containsneither
--src_regionalnor--dest_regional.3 passed.Visual evidence
I think it is likely (though I have not tested) that the
--src_regional --dest_regionalcontradictory combination results in some really minimal regrid errors at all places/times. As demonstrated below it does cause the regrid to implode really spectacularly in the New Zealand area. The NZ ERA5 met regrid put pronounced East-West stripes into the regridded data:regridded ERA5 t2m with
-r(looks like New Zealand 👍):regridded ERA5 t2m with
--src_regional --dest_regional(does NOT look like New Zealand 😭):I generated the below diagnostic images while investigating a regional-grid failure. The longitude error field showed pronounced horizontal striping without the dual-regional option; with
-r, it is reduced to the small numerical residual expected from coordinate transformation and interpolation.Before: longitude error with
--src_regional --dest_regional:After: longitude error with
-r:Before: latitude error with
--src_regional --dest_regional:After: latitude error with
-r: