Toy Terminator Chemistry

The simpler model configurations described in this page are in development and will be considered for integration into the standard CESM Simpler Models after consideration and discussion at upcoming Atmosphere Model Working Group meetings, and in consultation with Lorenzo Polvani ( or Amy Clement (

Note, the following instructions are only valid for the development version of CESM. If you wish to run this test case configuration, please contact Peter Hjort Lauritzen ( or Steve Goldhaber (

This test extends the evaluation of transport schemes from prescribed advection of inert scalars to reactive species. The test consists of transporting two reacting chlorine-like species (Cl and Cl2). The sources and sinks for the two species are given by a simple, but non-linear, 'toy' chemistry. This chemistry mimics photolysis-driven processes near the solar terminator. As a result, strong gradients in the spatial distribution of the species develop near the edge of the terminator. Despite the large spatial variations in Cl and Cl2 the weighted sum Cly=Cl+2Cl2 should always be preserved regardless of the flow field. The terminator test demonstrates how well the advection/transport scheme preserves linear correlations. Physics-dynamics coupling can also be studied with this test. For more information on the terminator chemistry see Lauritzen et al. (2015).

The terminator chemistry can be turned on in any CAM configuration. The terminator chemistry flag will add the two tracers, Cl and Cl2, and invoke the idealized chemical reactions. For simplicity we document the terminator chemistry with the moist baroclinic wave with Kessler microphysics below.

Running the FKESSLER test case (with terminator chemistry)

After downloading the latest CESM code base, users may perform this test by following the procedures outlined below.  See the CESM user's guide for more infomation on creating and running new cases. 

The FKESSLER compset automatically turns on the terminator chemistry.

Step 1: Create the FKESSLER test case

This can be done using the create_newcase script located in the directory $CESM/cime/scripts/ e.g., for the f09_f09 resolution

./create_newcase -compset FKESSLER -res f09_f09 -case $CASEDIR --run-unsupported

 where the case directory is $CASEDIR. -res f09_f09 sets the dynamical core to the finite-volume dynamical core at 1 degree horizontal resolution. Replace -res f09_f09  with -res f19_f19  for the 2 degree horizontal resolution finite-volume dynamical core or -res ne30_ne30  for the 1 degree horizontal resolution spectral-element dynamical core. Any supported dynamical core and supported resolution for that particular dynamical core in CESM can be used (see source code file components/cam/bld/config_files/horiz_grid.xml).

Step 2: Configure the FKESSLER test case

The FKESSLER compset ensures that most of what is necessary to perform the test case is set up automatically.  The default length of the simulation is set to 5 days, so in order to perform a 12 day test case, the following command must be invoked

./xmlchange STOP_OPTION=ndays,STOP_N=12

For short simulations generating relatively small output files it is sometimes convenient to turn off the automatic archiving functionality in the CESM scripts:

./xmlchange DOUT_S=FALSE

If you want to see what configuration options you are using use

./xmlquery CAM_CONFIG_OPTS

which will generate the following output:

CAM_CONFIG_OPTS: -phys kessler -chem terminator -analytic_ic

The -chem terminator is the configure option that invokes terminator chemistry.

Step 3: Set up and build the FKESSLER test case

From within $CASEDIR run


Step 4: Run the FKESSLER test case


Step 5: Validate the FKESSLER terminator chemistry output

A number of fields can be used to check that the simulation has produced correct output. Three such fields are shown below.

Figure: Column-integrated mass-weighted averages of CL, CL2 and CLy.

Column-integrated mass-weighted averages of CL, CL2 and CLy

These plots can be reproduced using an ncl script that can be downloaded here