Exercise 3: Change physics timestep

Exercise 3: Change physics timestep#

Exercise: Change physics timestep in CAM and CLM

Hybrid start a fully coupled run under pre-Industrial conditions with a resolution of f19_g17. Use restart and initial files from Exercise 2. Change the physics timestep in the atmosphere and land to 1200 seconds (default is 1800). Run 5 days.

Hint!

The atmosphere physics timestep is determined by the base period of coupling NCPL_BASE_PERIOD and the coupling frequency ATM_NCPL.
Find out their default values using xmlquery.

Click here for the solution

1. From the script directory, create your case:

    cd /glade/work/$USER/code/my_cesm_code/cime/scripts/
    ./create_newcase --case /glade/work/$USER/cases/b.day2.3 --res f19_g17 --compset B1850

2. In your case directory, change run type and runtime variables:

    cd /glade/work/$USER/cases/b.day2.3
    ./xmlchange RUN_TYPE=hybrid,RUN_REFCASE=b.day2.2,RUN_REFDATE=0001-06-01,GET_REFCASE=FALSE,JOB_WALLCLOCK_TIME=2:00:00

3. Change the physics timestep for CAM:

    ./xmlchange ATM_NCPL=72

(Why ATM_NCPL = 72? Do the math).

4. Set up the case and position your initial and restart files in the `$RUNDIR`:

    ./case.setup
    cp /glade/scratch/$USER/archive/b.day2.2/rest/0001-06-01-00000/*  /glade/scratch/$USER/b.day2.3/run/

5. Continue to build and submit:

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

Remember that qcmd is used on Cheyenne only.