[BUG/ISSUE] Resolution-dependent bias in surface ozone in 12.5.0

[geoschem]

[BUG/ISSUE] Resolution-dependent bias in surface ozone in 12.5.0

[lizziel]

FV3 is moving to a new repository on GEOS-ESM and GEOS-ESM/GEOSgcm_GridComp#48 will be moved. Information about changes to this issue will be documented here for the GCHP community.

[lizziel]

This issue persists in dev versions of 13.0.0 which uses MAPL 2.0.

[lizziel]

This ozone bias in the southern hemisphere is fixed by switching the regridding method of winds from bilinear interpolation to conservative. This update should be made in ExtData.rc for UC;UV, ULL, UVV, U, and V. The update will go into 12.8.0.

[lizziel]

The switch to conservative winds regridding introduced a polar stratospheric NOy source in the Arctic. We are now delaying making the fix default until the source of this is better understood. It will not be included in 12.8.

The 1-month benchmark plots for before and after the fix are located here if you would like to take a look: http://ftp.as.harvard.edu/gcgrid/geos-chem/validation/GCHPctm/13.0.0-alpha.3/

[lizziel]

The surface ozone bias fix will be included in 12.8 after all. It appears that the polar stratospheric NOy source in the Arctic was a compute cluster fluke, although we are on the lookout for seeing something like it again. Rerunning a 1-month benchmark run made it go away.

The update to fix the ozone bias requires a minor update to MAPL, also to be included in 12.8.0. A remnant of pre-12.5 MAPL remained post-12.5 in which the run was forced to stop if conservative regridding of vectors (winds in our case) was turned on. This alarm was spurious and conservative regridding of vectors is actually possible. The GCHP repository update for 12.8 therefore comments out that forced stop. See geoschem/GCHP@ffb5a09.

This update can be applied to earlier versions of GCHP to bypass the surface ozone bias. Simply change ExtData.rc regrid method for winds from N to Y in the conservative column, and apply the GCHP commit above.

[sdeastham]

@lizziel Do you think it's safe to close this issue then?