Add output variable in CAM#

Exercise: Add an additional output variable

Create a case called b1850_T750 using the compset B1850 at f19_g17 resolution.

  • Add an output field for the temperature at 750 mbar.

  • Output daily values of T750 and T500 in the h1 history file.

  • Set the namelist to output a single h1 for the run.

  • Make a 1-month run.

Click here for hints

Tip to add T750

  • Use T500 as a template for your changes.

  • Find the subroutine containing T750. For instance, in the CESMROOT, use the command:

    grep –r T500 *

Tip to check your solution T750

  • When the run is completed, go to your archive directory:

  • check the fields T750 and T500 are in the file h1

  • create a file with the difference between T750-T500

  • For instance, you can use ncap2

    ncap2 -s ’T750_minus_T500=T750-T500' b1850_T750.cam.h1.0001-01-01-00000.nc  T750-T500.nc

  • Look at the difference with ncview.

    ncview T750-T500.nc
Click here for the solution

# Create a new case

Create a new case b1850_T750 with the command:

 cd /glade/work/$USER/code/my_cesm_code/cime/scripts/
./create_newcase --case ~/cases/b1850_T750 --compset B1850 --res f19_g17

# Setup

Invoke case.setup with the command:

cd ~/cases/b1850_T750
./case.setup

# Make Source Modifications
Use T500 as a template for your changes. For that purpose, locate the file where T500 is computed and copy it into SourceMods/src.atm:

cp /glade/p/cesm/tutorial/cesm2.1_tutorial2022/components/cam/src/physics/cam/cam_diagnostics.F90 SourceMods/src.cam

Now, let’s use T500 as a template for your changes and add the relevant lines for T750: edit the file SourceMods/src.cam/cam_diagnostics.F90 to add the following.

First change

Under the lines:

!++ add a variable for T500 
call addfld ('T500', horiz_only,  'A', 'K','Temperature at 500 mbar pressure surface')

add the lines:

!++ add a variable for T750 
call addfld ('T750', horiz_only,  'A', 'K','Temperature at 750 mbar pressure surface')

Second change Under the lines:

!++ add a variable for T500 
if (hist_fld_active('T500')) then 
    call vertinterp(ncol, pcols, pver, state%pmid, 50000._r8, state%t, p_surf, & 
         extrapolate='T', ps=state%ps, phis=state%phis)
    call outfld('T500    ', p_surf, pcols, lchnk )
end if

add the lines:

!++ add a variable for T750 
if (hist_fld_active('T750')) then 
    call vertinterp(ncol, pcols, pver, state%pmid, 75000._r8, state%t, p_surf, & 
         extrapolate='T', ps=state%ps, phis=state%phis)
    call outfld('T750    ', p_surf, pcols, lchnk )
end if

# Customize namelists Edit the file user_nl_cam and add the lines:

    nhtfrq = 0, -24
    mfilt = 1, 31
    fincl2 = 'T750', 'T500'

# Set run length

Set the run length to 1 month:

./xmlchange STOP_N=1,STOP_OPTION=nmonths

# Change the job queue and account number

If needed, change job queue and account number.
For instance, to run in the queue regular and the project number P93300642, use the command:

./xmlchange JOB_QUEUE=regular,PROJECT=P93300642

# Build and submit

Build the model and submit your job:

qcmd -- ./case.build
./case.submit

# Look at your solution

When the run is completed, check the fields T750 and T500 are in the file h1:

cd /glade/scratch/$USER/archive/b1850_T750/atm/hist/ 
ncdump -h b1850_T750.cam.h1.0001-01-01-00000.nc

The file should contain:

float T500(time, lat, lon) ;
    T500:units = "K" ;
    T500:long_name = "Temperature at 500 mbar pressure surface" ;
    T500:cell_methods = "time: mean" ;
float T750(time, lat, lon) ;
    T750:units = "K" ;
    T750:long_name = "Temperature at 750 mbar pressure surface" ;
    T750:cell_methods = "time: mean" ;

If you don’t see these variables, check you correctly set the user_nl_cam.

Create a file with the difference between T750-T500:

cd /glade/scratch/$USER/archive/b1850_T750/atm/hist/ 
ncap2 -s 'T750_minus_T500=T750-T500' b1850_T750.cam.h1.0001-01-01-00000.nc  T750-T500.nc

Look at the difference between T750-T500 with ncview:

cd /glade/scratch/$USER/archive/b1850_T750/atm/hist/ 
ncview T750-T500.nc

The field T750-T500 looks like:

ncview T750-T500
Figure: Overview of the CESM directories and the SourceMods directories.