Problem changing namelist variable in N1PCTcmip6frc2

[rsteene]

I am trying to change the flbc_file through user_nl_cam in a N1PCTcmip6frc2 compset, but it does not write to atm_in. The exact same thing works well when I change to a SSP compset, but when using N1PCTcmip6frc2 the flbc_file does not change. Can anyone tell me why?

[gold2718]

The N1PCTcmip6frc2 is a CMIP6 DECK 1pctCO2 experiment which forces CO2 to increase by 1% per year (other forcings are maintained at the 1850 piControl levels).
For these experiments, the flbc_file is set in CAM's config_component.xml file. These values override any setting in user_nl_cam.
You could override the setting in config_component.xml. While this likely changes the compset away from its 1% ramp it is possible.

[rsteene]

Thanks for your reply! Yes, I want to do a run where CO2 increases with 1% per year like in N1PCTcmip6frc2, but then decrease it again after a given amount of years. And I also want to extend the run (and therefore the flbc_file) beyond 165 years. So I think overriding the config_component.xml setting is what I want to do? How can I accomplish that?

[gold2718]

My approach would be to create a branch from the tag you are working with and change that file. I think the line you want to change is:

<value compset="_CAM60%NORESM%FRC2%1PCT"  > flbc_file='$DIN_LOC_ROOT/atm/waccm/lb/LBC_CMIP6_1pctCO2_y1-165_GlobAnnAvg_0p5degLat_c180929.nc'</value>

probably somewhere around line 416 in your <NorESM>/components/cam/cime_config/config_component.xml file.

[rsteene]

Thank you! I will give that a try.