2: Turn off parameterization#

Oceanic overflows are dense currents originating in semienclosed basins or continental shelves. They contribute to the formation of abyssal waters and play a crucial role in large-scale ocean circulation. When these dense currents flow down the continental slope, they undergo intense mixing with the surrounding (ambient) ocean waters, causing significant changes in their density and transport (see figure below). However, these mixing processes occur on scales that are smaller than what ocean climate models can accurately capture, leading to poor simulations of deep waters and deep western boundary currents. To improve the representation of overflows some ocean climate models rely on overflow paramterizations, such as the one developed for the POP model (check this report for additional information).

overflows

Figure: Physical processes acting in overflows (from Legg et al., 2009)

Exercise: Turn off overflow parameterization

Create a case called g_overflows by cloning the control experiment case.

Verify that the run length is set to 1 year.

In user_nl_pop make the following modifications:overflows_on = .false. and overflows_interactive = .false.

Build and run the model for one year.

Compare the simulations using ncview/ncdiff, etc.

Click here for hints

How do I compile and run?

You can compile with the command:

qcmd -- ./case.build

You can run with the command:

./case.submit

How do I check the lenght of the run?

Use xmlquery to search for the variables that control the run length

Click here for the solution

Clone a new case g_overflows from your control experiment with the command:

cd /glade/work/$USER/code/my_cesm_code/cime/scripts/
./create_clone --case /glade/work/$USER/cases/g_overflows --clone /glade/work/$USER/cases/g_control

Case setup:

cd /glade/work/$USER/cases/g_overflows
./case.setup

Verify that the run length is 1 year:

./xmlquery STOP_N
./xmlquery STOP_OPTION

Edit the file user_nl_pop and add the lines:

 overflows_on = .false.
 overflows_interactive = .false.

If needed, change job queue and account number. For instance:

./xmlchange JOB_QUEUE=regular,PROJECT=UESM0011

Build and submit:

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

When the run is completed, look into the archive directory for: g_overflows.

(1) Check that your archive directory on cheyenne (The path will be different on otehr machines):

cd /glade/scratch/$USER/archive/g_overflows/ocn/hist
ls

Test your understanding#

  • What variables do you expect to change when you turn off the overflow parameterization?

  • What variables show a difference between this experiment and the control difference? How different are they?