Experiment with the Atmosphere


Teaching: min
Exercises: min
  • How do I setup and run an experiment with prescribed ocean forcing?

  • How is the ocean forcing defined?


In this lesson, we will learn about setting up experiments using the atmosphere with the ocean in data mode with prescribed SST forcing.

We will start with a basic case of running an atmosphere-forced experiment. We will then consider a specific scientific question and setup experiments using the atmosphere-forced experiment to answer this question, following the Drought Working Group Experiments.

Running the Atmosphere

Anytime we want to setup a new expeiment, we will create a newcase using the create_newcase script. The script requires us to provide several things when we run it. Let’s figure out the correct options for setting up a case with the atmosphere in forced mode.

--case ~/case/casename We can name our case whatever we want

--res f19_g17 We are using this resolution, but we will need to check if it is available for what we want to do

--compset COMPSET We will need to determine the right compset for this experiment.

--project UGMU0032 This is our project code. It does not change.

What compset do we use?

There are two ways to determine which compset to use.

  1. There is a tool:
$ CIMEROOT/scripts/query_config --compsets

We can see from this that the compsets with cam, the atmosphere model, active all start with F, but it gives us the complicated long name and doesn’t provide us with all the information we need. Let’s take a look at the website for more information.

Notice that the website indicates which version of CESM you are using in the upper right corner. Our version is CESM 2.1.1. Let’s scroll until we find the F compsets.

There are several options here, but the most basic option is FHIST. This is an atmosphere forced run with prescribed ocean and ice using historical GHG forcing.

Remember that the compset determines which grids are scientifically validated, meaning which ones have been tested.

Is our resolution grid scientifically validated for any of the F compsets?

Take a look at the webpage and view the scientifically validated grid for the F-composets. See if our grid is listed.

Create your case

Create a new case using the FHIST compset with our grid and project code Call the case whatever you wish.

$ ./create_newcase --case ~/cases/testatmF --res f19_g17 --compset FHIST --project UGMU0032

You will get an error. Read the error.

What does it mean? What do you need to do to setup your case with this compset and grid resolution?


create_newcase is letting us know that our grid is not scientifically validated for this compset. It tells us we can use the --run_unsupported option to use this grid and compset anyway.

$ ./create_newcase --case ~/cases/testatmF --res f19_g17 --compset FHIST --project UGMU0032 --run-unsupported

Complete the setup, build the case and run it for 1-month as a test


$ ./case.setup
$ qcmd -- case.build
$ ./xmlchange STOP_OPTION=nmonths
$ ./xmlchange STOP_N=1

How is the ocean prescribed in this run?

Full documentation on DOCN is here

The file specifying the SST and Ice data is located in SSTCE_DATA_FILENAME. We can use xmlquery to see what this is set to.

	SSTICE_DATA_FILENAME: /glade/p/cesmdata/cseg/inputdata/atm/cam/sst/sst_HadOIBl_bc_1x1_1850_2017_c180507.nc
Let’s look at the description of this variable in env_run.xml:
Prescribed SST and ice coverage data file name. Sets SST and ice coverage data file name. This is only used when DOCN_MODE=prescribed.

Based on the filename, this appears to be SST and Ice data on a 1x1 degree grid from 1850-2017. We can do ncdump -h on the file to get more information.

$ ncdump -h /glade/p/cesmdata/cseg/inputdata/atm/cam/sst/sst_HadOIBl_bc_1x1_1850_2017_c180507.nc

The data contains several variables: ice_cov, SST_cpl, etc. The global attributes tell us how this data was made and even give us a reference for it. We can look this up in more detail if we want. For now, let’s take a look at the data using ncview.

$ module load ncview
$ ncview /glade/p/cesmdata/cseg/inputdata/atm/cam/sst/sst_HadOIBl_bc_1x1_1850_2017_c180507.nc

We now know how to create a case with ocean prescribed.

We know how to set the file that prescribes the ocean.

We have an example file that prescribes the ocean.

Key Points