CESM picontrol run with weird CO2 trend

[nlaureanti]

What version of the code are you using?
release-cesm2.2.2

Have you made any changes to files in the source tree?
No


Describe every step you took leading up to the problem:
I'm testing two experiments with the same compset and model version.

./create_newcase --case ./b.e21.B1850.f09_g17.CMIP6-piControl.001 --compset B1850 --res f09_g17
./create_newcase --case ./b.e21.B1850.f09_g17.CMIP6-esm-piControl.001.test2 --compset B1850 --res f09_g17

The first is a pi-Control case b.e21.B1850.f09_g17.CMIP6-esm-piControl.001, that takes a restart file from 501-01-01 spin-up (which I imagine is from another version) and the case b.e21.B1850.f09_g17.CMIP6-esm-piControl.001.test2 as spin-up for this version of the model running in our cluster (but has only 30 years).

Describe your problem or question:

Hi all, I'm running two simple piControl runs. I haven't changed any of the CO2 parameters. As you can see in the images, the CO2 starts around 285ppm and is decreasing to 270 ppm in 20 years. I'm using the parameters as the default for the case, basically:

&co2_cycle_nl
 co2_flag        = .true.
/
&chem_surfvals_nl
 ch4vmr        =    791.6e-9   
 co2vmr        =    284.7e-6   
 f11vmr        =    12.48e-12 
 f12vmr        =    0.0       
 flbc_list        = ' '
 n2ovmr        =    275.68e-9 
/

I wonder if I need to change the CO2 parameters to run the piControl as the CMIP6. Or should I test another version of the model? Could you please guide me on this issue?
Thanks a lot!

 

[hplin]

Hi Nicole, thanks for writing. I am forwarding to the CAM forum to help diagnose the CO2 issue. The namelist parameters you provided seems to match https://svn-cesm2-expdb.cgd.ucar.edu/public/b.e21.B1850.f09_g17.CMIP6-piControl.001/CaseDocs/atm_in but you are correct that it is from a different version.

The original runs were on CESM2.1 and I believe that is still the recommended version for CMIP6-related simulations so I would try to run with CESM2.1 to see if the issue still persists in that version.