Exercise#

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.

  • Make a 5-day run.

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

  • One the run is completed, check the contents of your archive directory to make sure it has worked. You can also check if the output makes sense by using the analysis notebook `~/analysis_notebooks/codemods/compare_T750_T500.ipynb’

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 CAM source code directory within 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

    ncdump -h b1850_T750.cam.h1.0001-01-01-00000.nc

  • You can also open up the analysis notebook ~/analysis_notebooks/codemods/compare_T750_T500.ipynb by navigating to it in the left hand panel. You can execute the scripts to make a plot of the difference between T750 and T500. You should see that T750 is warmer than T500 by between 10 and 25K.

Click here for the solution

# Create a new case

Create a new case b1850_T750 with the command:

cd $CESMROOT/cime/scripts
./create_newcase --case ~/cases/b1850_T750 --compset B1850-tutorial --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:

You can locate where T500 is computed by going into the CAM source code directory and searching for T500 using grep

cd $CESMROOT/components/cam/src
grep -r 'T500' *

Here you should find that ‘T500’ is computed and output in the cam_diagnostics.F90 subroutine within cam physics. So copy cam_diagnostics.F90 into your CAM SourceMods directory

cd ~/cases/b1850_T750
cp $CESMROOT/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:

call addfld ('T500', horiz_only,  'A', 'K','Temperature at 500 mbar pressure surface')

add the lines:

call addfld ('T750', horiz_only,  'A', 'K','Temperature at 750 mbar pressure surface')

Second change

Under the lines:

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:

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, 5
    fincl2 = 'T750', 'T500'

# Build and submit

Build the model and submit your job:

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