ctsm5.4.002

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Tag name: ctsm5.4.002
Originator(s): erik (Erik Kluzek,UCAR/TSS,303-497-1326)
Date: Wed Dec 10 03:35:12 PM MST 2025
One-line Summary: Start using CMIP7 Carbon Isotope datasets

Purpose and description of changes
----------------------------------

By default read in the cmip7 c13/c14 stream files rather than the previous cmip6 ones. Read in the cmip6 ones if CLM_CMIP_ERA=cmip6 and use_c13/use_c14 are on.

Found problems with the "nn" nearest-neighbor interpolation in streams. Added a new test on Derecho
to turn on nn for several of the streams. These problems go away when using ESMF-8.9.0 or later.

Significant changes to scientifically-supported configurations
--------------------------------------------------------------

Does this tag change answers significantly for any of the following physics configurations?
(Details of any changes will be given in the "Answer changes" section below.)

[Put an [X] in the box for any configuration with significant answer changes.]

[ ] clm6_0

[ ] clm5_0

[ ] ctsm5_0-nwp

[ ] clm4_5

Bugs fixed
----------

List of CTSM issues fixed (include CTSM Issue # and description) [one per line]:
Fixes #182 -- c13/c14 isotope time-series is awkward for 1850 control (convert to streams file)

Notes of particular relevance for users
---------------------------------------

Changes to CTSM's user interface (e.g., new/renamed XML or namelist variables):
CLM_CMIP_ERA also changes Carbon isotope streams from cmip6 or cmip7

Changes made to namelist defaults (e.g., changed parameter values):
CMIP7 Carbon Isoptope datasets are used when use_c13/c14 is on and CLM_CMIP_ERA==cmip7

Notes of particular relevance for developers:
---------------------------------------------
Caveats for developers (e.g., code that is duplicated that requires double maintenance):
cmip_era is now an attribute for C13/C14 timeseries files
Changes to tests or testing:
Added stream input history output to the f09_ObscureStreams testmod
Added a new test with nn for streams

Testing summary: regular
----------------
[PASS means all tests PASS; OK means tests PASS other than expected fails.]

build-namelist tests (if CLMBuildNamelist.pm has changed):

derecho - OK

regular tests (aux_clm: https://github.com/ESCOMP/CTSM/wiki/System-Testing-Guide#pre-merge-system-testing):

derecho ----- OK
izumi ------- OK

If the tag used for baseline comparisons was NOT the previous tag, note that here:


Answer changes
--------------

Changes answers relative to baseline: Yes! (Just when Carbon Isotopes and timeseries is turned on)

Summarize any changes to answers, i.e.,
- what code configurations: Any physics with use_c13/c14 on and use_c13_timeseries/c14_bombspike on, CLM_CMIP_ERA=cmip7
- what platforms/compilers: All
- nature of change (roundoff; larger than roundoff/same climate; new climate): adjusted climate for C13/C14
Changes answers for clm4_5, clm5_0 and clm6_0 physics options when Carbon Isotopes are on
Doesn't change answers for non C13/C14 fields
Doesn't change answers if CLM_CMIP_ERA=cmip6

Other details
-------------

Pull Requests that document the changes (include PR ids):
(https://github.com/ESCOMP/ctsm/pull)
#3634 -- CMIP7 Carbon Isotopes on by default


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