Graduate Student Test: MR Weather App CCN Experiment

Test Description

This test assesses how easy it is to access and run a UFS code, modify a physics parameter, re-run the code and then compare results. The test case is a hurricane Dorian simulation using the UFS Medium-Range Weather Application. It is an example of a code usability evaluation following the "graduate student test" protocol developed for the Unified Forecast System (UFS).

In order to perform the test, you will run the model for 48 hours, use the workflow software to make a change in the namelist that increases the concentration of cloud condensation nucleii (CCN), and perform another 48 hour run with this change. Then you will compare the total cloud cover field before and after the change.

Cloud condensation nuclei (CCN) are small particles suspended in the atmosphere on which water vapor condenses. The number of nuclei per cubic centimeter is used in the microphysics parameterization. With more CCN in the air, cloud water is distributed over a larger number of smaller drops. This hinders the development of precipitation processes, so droplets stay suspended and cloud coverage is higher. Even after just 48 hours, an increase can be seen in the cloud cover field. As the forecast progresses, nonlinear processes take place and can change this simple interpretation.

Run the Control Case

Follow the instructions on the Getting Started page to run the Hurricane Dorian case at C96 resolution, with the GFSv15p2 physics, without the post-processor turned on, for two days.

Run the Experiment

You will need to create another case directory for the experiment, and setup and build the new case.

$ cd $HOME/my_ufs_sandbox/cime/scripts
$ ./create_newcase --case DORIAN_C96_GFSv15p2_EXP --compset GFSv15p2 --res C96 --workflow ufs-mrweather
$ ./case.setup
$ ./case.build

Look at the values of ccn_l and ccn_o using preview_namelists - check the input.nml file.

You should see: