Add reader for surface meteorological forcing from S2S-3

[gmao-qliu]

We need to read S2Sv3 output for offline forecast experiments. Since S2Sv3 doesn't output 3-hourly downward shortwave and longwave radiation, we could rename the land forcing variables in post-processing. Ideally, we would extend get_GEOS() to read both S2Sv3 Forecast and Analysis outputs.

Related PRs:
GEOSldas PR#831

Successfully 0-diff tested for standard Intel builds after

• ff95e4e (14 Aug 2025) by @gmao-rreichle
• fe7b771 (20 Aug 2025) by @gmao-rreichle

[gmao-qliu]

@gmao-rreichle I updated the code. Please begin reviewing the changes.

MET_TAG for S2Sv3 would be:
GEOSS2S3FCST__ens?__YYYYMMDD for forecast forcing
and
GEOSS2S3AODAS for analysis forcing. AODAS forcing data will be stored in daily files under the usual GEOS directory structures (/diag/Y../M../)

[gmao-rreichle]

@gmao-qliu : I think I have something that should be close to working as desired. Pls note the comment below. We also still need to add documentation of the new reader in the GEOSldas repo: doc/README.MetForcing_and_BCS.md, see GEOS-ESM/GEOSldas#831

PS: The revised implementation requires that the 'time_increment' (sp?) attribute is available in the nc4 file or otherwise finds its way into LDAS_GetVar().

[gmao-qliu]

PS: The revised implementation requires that the 'time_increment' (sp?) attribute is available in the nc4 file or otherwise finds its way into LDAS_GetVar().

I tested this revision with "time_increment" attribute. It does work.