Exercise 1#
We’ll start with a simple example: doubling the CO2 concentration
Exercise: Doubling the CO2 concentration
Make a new case using the B1850-tutorial
compset and f19_g17
resolution. Put it in ~/cases
and call it b1850_2x
.
Set up the case and preview the namelists. You can preview the namelists that the case is using with the following command in your case directory
./preview_namelists
Check that the value of co2vmr
in CaseDocs/atm_in
and in the run directory.
Double the CO2 concentration and preview the namelists again.
Check that the value of co2vmr
changed in CaseDocs/atm_in
and in the run directory.
Note: You don’t need to build (qcmd -- ./case.build
) and submit (./case.submit
). We are just looking at namelists without running the case.
Click here for hints
How to preview namelists
You can preview the namelists that the case is using with the following command in your case directory
./preview_namelists
This will generate files with names XXX_in where XXX corresponds to the model component e.g.,
atm_in
for the atmosphere component. These files are generated both in the CaseDocs sub-
directory of your case directory and the run directory. Take a look at ./CaseDocs/atm_in
.
How to double the CO2 concentration
Now for the B1850-tutorial
compset, CO2 concentrations are controlled by the namelist parameter co2vmr
i.e., CO2 volume mixing ratio.
You should see in the atm_in file that it is currently set to
co2vmr=284.7e-6
To double the CO2 concentration we need to modify co2vmr
by setting it to the value we want
in the user_nl_cam file. DO NOT change it in the atm_in
file. That will not affect the
simulation. The atm_in
file is generated simply for reference when the case is built
or submitted. So place the following entry in user_nl_cam
co2vmr=569.4e-6
Has your change been propagated to the atm in file after running preview_namelists
?
How to edit the user_nl_cam
Use a text editor as explained in the nano editor section.
Click here for the solution
To create a new case using the B1850-tutorial
compset with f19_g17 resolution you can do the following
cd $CESMROOT/cime/scripts
./create_newcase --case ~/cases/b1850_2x --compset B1850-tutorial --res f19_g17
Now, go to the case directory and set up your case
cd ~/cases/b1850_2x
./case.setup
You can check the default value of co2vmr by previewing the namelists
./preview_namelists
and searching for the variable co2vmr in ./CaseDocs/atm_in
within your case directory
grep 'co2vmr' ./CaseDocs/atm_in
Now add the following line to user_nl_cam
co2vmr=569.4e-6
Now run
./preview_namelists
and check your changes have propagates to the namelist i.e., examine the files
~/cases/b1850_2x/CaseDocs/atm_in
and
~/scratch/b1850_2x/run/atm_in
We’re not doing this here, but if you wanted to actually submit the run, you’d do
qcmd -- ./case.build
./case.submit