noresm3_0_044_cam6_4_121: new nearest_lat mapalgo in cdeps - does not requre a mesh

[mvertens]

Summary

Added new nearest_lat mapping option for CO2 surface source override. Previously the stream was always regridded with bilinear, which required a mesh file. The nearest_lat option lets forcing data that is purely latitude-based (lat/time or lat/lev/time) be mapped directly onto the model grid without a mesh file.

Changes

src/cpl/nuopc/atm_stream_co2.F90

• Added two new namelist variables: stream_co2_surface_source_mapalgo (defaults to nearest_lat) and stream_co2_surface_source_lat_dimname.
• If tream_co2_surface_source_mapalgo is set to 'nearest_lat - then
  • The mesh file must be set to 'none'
  • The stream_co2_surface_source_lat_dimname must be set (currently should be 'lat') for the datasets that are being used

bld/build-namelist

• Requires the two new variables to be defined when co2_surface_source is .true..
• Adds a consistency check: if mapalgo is nearest_lat, the mesh filename must be none.

bld/namelist_files/namelist_definition.xml

• Documents the two new namelist entries and updates the mesh-filename entry to note it must be none for nearest_lat.

NOTE: - this PR requires the companion CDEPS change that implements the mesh-free nearest_lat mapalgo - NorESMhub/CDEPS#40.

Testing:
Using the following compset/resolution

--compset 1850_CAM70%LT%NORESM%CAMoslo_CLM60%FATES-NCFB%NORESM_CICE_BLOM%HYB%ECO_MOSART_DGLC%NOEVOLVE_SWAV_SESP 
--res ne16pg3_tn14

And the following namelist setting in user_nl_cam

co2_surface_source = .true.
stream_co2_surface_source_data_filename = 
stream_co2_surface_source_data_filename = '$DIN_LOC_ROOT/atm/waccm/lb/cmip7_ghg_version20260727/ghg_cmip7_CMIP_CR-CMIP-1-0-0_1750-2023_monthly_gnz_0p5degLat_version20260727.nc'
stream_co2_surface_source_data_varname = 'CO2_LBC'
stream_co2_surface_source_mesh_filename = 'none'
stream_co2_surface_source_mapalgo = 'nearest_lat'
stream_co2_surface_source_lat_dimname = 'lat'
stream_co2_surface_source_taxmode = 'extend'
stream_co2_surface_source_year_first = 1850
stream_co2_surface_source_year_last = 2023
stream_co2_surface_source_year_align = 1

Verified that the resulting coupler history file looked correct.

[mvertens]

@DirkOlivie @gold2718 - currently using the nearest_lat mapping requires new files that have a _time.nc suffix (the original files did not have valid values for the time variables). I'd like to replace the files in atm/waccm/lb/cmip7_ghg_version20260607/ that have no _time suffix with those that do have the _time suffix for backwards compatibility. In that case there are no different files that have to be used in order to leverage the co2 surface override capability.

[gold2718]

I have a question and there is at least one typo.

[gold2718]

Looks great, thanks!