changing co2 in cam5

[hannay]

From user:

I am trying to run CAM5 with 4xCO2 in our local machine.

Could you tell me what I need to add in atm_in file or other files to make 4xCO2 run?

I add ‘co2vmr = 1516.000e-6’ in atm_in. But the output co2vmr is still original value.

There must be other parameter needs to be modified.

Appreciate your help in advance!

 

[hannay]

You need to set your namelist changes in user_nl_cam not in atm_in. Changes on atm_in will be overwritten. Instructions how to change namelist variables can be found in: https://www.cesm.ucar.edu/events/tutorials/2021/files/Practical4-introduction-hannay.pdf

Changing the CO2 value with the co2vmr namelist variable won't work in every configuration. In some configurations, the CO2 is set as a constant with the co2vmr (for instance for a B1850 with CESM1 or CESM2) but in other configurations, the CO2 will be varying year to year and it will be set in a netcdf file with the variable flbc_file or the variable bndtvghg

For instance in a B1850 with CESM2, the greenhouse gases are set to a constant value.

ch4vmr         =    791.6e-9   
 co2vmr         =    284.7e-6   
 f11vmr         =    12.48e-12 
 f12vmr         =    0.0       
 flbc_list              = ' '
 n2ovmr         =    275.68e-9

For instance in a FHIST or a BHIST with CESM2:

flbc_file              = '/glade/p/cesmdata/cseg/inputdata/atm/waccm/lb/LBC_17500116-20150116_CMIP6_0p5degLat_c180905.nc'
flbc_list              = 'CO2','CH4','N2O','CFC11','CFC12','CFC11eq'
flbc_type              = 'SERIAL'
scenario_ghg           = 'CHEM_LBC_FILE'

Or for instance in a FAMIPC5 or B20TR with CESM1:

bndtvghg               = '/glade/p/cesmdata/cseg/inputdata/atm/cam/ggas/ghg_hist_1765-2005_c091218.nc'
co2vmr         = 284.7e-6
flbc_list              = ' '
scenario_ghg           = 'RAMPED'

 

[hannay]

From user:

I check the link in your email and also ppt file for how to modify usr_nl_atm.

But that is for CESM2 and CAM6. For CESM1 and CAM5, there is no usr_nl_atm file for the case I created.

This is the commend I used to create the case for the control run,

create_newcase -mach generic_linux_intel -scratchroot /ptmp/CAM5/run -din_loc_root_csmdata /ptmp/CAM5/inputdata -max_tasks_per_node 8 -compset F_AMIP_CAM5 -res f19_f19 -case /ptmp/CAM5/run/cam5.1_ctl

For the abrupt 4xCO2 run with CESM1 and CAM5, I used the following code in atm_in,

bndtvghg = '/glade/p/cesmdata/cseg/inputdata/atm/cam/ggas/ghg_hist_1765-2005_c091218.nc'

co2vmr = 1516.0e-6

flbc_list = ' '

scenario_ghg = 'RAMPED'

But there is only very small change in 4xCO2 run comparing with the control run. In the control run, co2vmr = 379.0e-6

Still not sure what is the right setup for an abrupt 4xCO2 run with CAM5.

 

[hannay]

Please look into the case directory:
/ptmp/CAM5/run/cam5.1_ctl
for the file:
user_nl_cam
This is where you would do your changes.
Note that the file called: user_nl_cam and not usr_nl_atm.

In your example, the greenhouse gases will be read from the file bndtvghg
bndtvghg = '/glade/p/cesmdata/cseg/inputdata/atm/cam/ggas/ghg_hist_1765-2005_c091218.nc'
scenario_ghg = 'RAMPED'

The variable
co2vmr
will be ignored.

You might be able to force the model to use co2vmr instead bndtvghg of by setting:
scenario_ghg = 'FIXED'


PS: If possible, please could you post further questions here instead of sending in a email. Thank you so much.

 

[wuxq]

There is no file user_nl_cam under /ptmp/CAM5/run/cam5.1_ctl, not sure why. But under /ptmp/CAM5/run/cam5.1_ctl/run, there is atm_in.

After changing RAMPED to FIXED, the run fails with co2vmr=1516.0e-6. But the run with co2vmr = 379.0e-6 is running ok with FIXED.

 

[hannay]

I am confused why there is no user_nl_cam under /ptmp/CAM5/run/cam5.1_ctl
As far as I know, you cannot change the namelist by directly modifying atm_in.
Any change you would do in /ptmp/CAM5/run/cam5.1_ctl/run/atm_in should be overwritten when you submit the run.
Which tag are you using? By tag I mean version of cesm. I want to try to reproduce the case directory.
Thanks.

 

[wuxq]

cesm1_0_3

 

[hannay]

This is a very old tag.

I believe that in the old days, there was a variable called CCSM_CO2_PPMV in the file env_conf.xml. If you change it there, it should propagate into co2vmr