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geoschem / geos-chem

GEOS-Chem "Science Codebase" repository. Contains GEOS-Chem science routines, run directory generation scripts, and interface code. This repository is used as a submodule within the GCClassic and GCHP wrappers, as well as in other modeling contexts (external ESMs).
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[FEATURE REQUEST] Retire met-field LWI in GC-Classic #1413

Closed lizziel closed 1 year ago

lizziel commented 2 years ago

This feature request is to (1) remove use of land-water-ice index (LWI) meteorology input in GC-Classic, and (2) remove the GEOS-Chem State_Met%LWI.

The motivation for this is the land-water-ice index in the GEOS-Chem input meteorology will not be available in the GEOS-IT dataset. Updates have already removed the dependency in GCHP by using other input met-fields to determine if each grid cell is predominantly land, water, or ice. https://github.com/geoschem/geos-chem/blob/412ba5906b2aa9dcd72a2188c76c50220c3697b7/Interfaces/GCHP/Includes_Before_Run.H#L65-L74

There is only one location in GEOS-Chem that uses LWI for computation, in dry deposition. https://github.com/geoschem/geos-chem/blob/412ba5906b2aa9dcd72a2188c76c50220c3697b7/GeosCore/drydep_mod.F90#L2271-L2273

GEOS-Chem also passes LWI to HEMCO which uses it in several extensions. HEMCO will thus need to be updated to use the available land type met-fields to do this instead, and I'll make a separate feature request in HEMCO for this.

I will work on getting this update into 14.1. It will impact the benchmark but the impact should be minor.

yantosca commented 2 years ago

For reference, here is the definition of LWI in GEOS-5.

LWI: A Land-Water-Ice mask provided for backward compatibility with the GEOS-4 product. It is 1 over continental areas, 0 over open ocean, and 2 over sea-ice covered ocean. Since in GEOS-5 a grid box can be a combination of these, continental areas are arbitrarily defined as those where FRLAND+FRLANDICE>=0.5. The remaining grid boxes are designated as sea-ice if the ice cover exceeds 50%; otherwise they are open (ice-free) ocean.

Note, this field was introduced in GEOS-5 for backwards compatibilty with the GEOS-4 SURFTYPE variable. LWI is going to be retired from the newer GEOS-IT dataset as it can be created from a combination of other fields:

lizziel commented 2 years ago

Thanks @yantosca. That definition of LWI interestingly does not say anything about FRLAKE (fraction lake). I've been qualifying grid cells as over continental land if FRLAND + FRLANDICE + FRLAKE is greater than both FROCEAN - FRSEAICE (open ocean) and FRSEAICE (ocean ice). If not continental land then I assign open ocean or ocean ice based on which fraction is larger. These are mostly used in HEMCO extensions to determine if over ocean, land, or ice. HEMCO includes an additional qualifier that FRLANDICE >= 0.5 be classified as ice. This is different from LWI that classifies ice as only over ocean.

How tied do you think we should be to the old GEOS-4 definition when switching from LWI to fraction land types?

yantosca commented 2 years ago

@lizziel, we probably shouldn't be too tied to GEOS-4.

lizziel commented 2 years ago

I have a couple draft PRs almost ready for review. Integration tests are in progress. https://github.com/geoschem/geos-chem/pull/1435 https://github.com/geoschem/HEMCO/pull/170

msulprizio commented 1 year ago

These PRs are now included in the dev/14.1.0 branch. I will close out this feature request.