3: Modify wind stress

Wind stress plays a critical role in driving ocean currents and is a key factor in shaping the overall patterns of large-scale ocean circulation and, consequentialy, the climate. Further details on how wind stress affects the ocean circulation are discussed in this manuscript.

Exercise: Increase zonal wind stress

Create a case called g.GW_JRA.TL319_t233_wg37.003 using the compset GW_JRA at TL319_t233_wg37 resolution.

Verify that the run length is set to 1 month.

Modify the subroutine mom_import in mom_cap_methods.F90 to increase the zonal (x) component of the wind stress by 25%.

Note: taux is the actual zonal wind stress in MOM6, while u_flux is the rotated component along the MOM6 grid lines, so here the change should be applied to taux.

Build and run the model for one month.

Compare the simulations using ncview/ncdiff, etc.

Click here for hints

Where is the source code?

You can find mom_cap_methods.F90 in /glade/u/home/$USER/cesm.code/cesm3_0_alpha09b/components/mom/MOM6/config_src/drivers/nuopc_cap/

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.GW_JRA.TL319_t233_wg37.003 from your control experiment with the command:

cd /glade/u/home/$USER/code/my_cesm_code/cime/scripts/
./create_newcase --case /glade/u/home/$USER/cases/g.GW_JRA.TL319_t233_wg37.003 --compset GW_JRA --res TL319_t233_wg37 --run-unsupported

Case setup:

cd /glade/u/home/$USER/cases/g.GW_JRA.TL319_t233_wg37.003
./case.setup

Verify that the run length is 1 month:

./xmlquery STOP_N
./xmlquery STOP_OPTION

Copy the mom_cap_methods.F90 file from the control case to the ocean SourceMods.

cp /glade/u/home/$USER/code/my_cesm_code/components/mom/MOM6/config_src/drivers/nuopc_cap/mom_cap_methods.F90 /glade/u/home/$USER/cases/g.GW_JRA.TL319_t233_wg37.003/SourceMods/src.mom/

Edit the file mom_cap_methods.F90 in the mom_import subroutine after taux is defined (line 164):

  taux(:,:) = taux(:,:) * 1.25

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

./xmlchange JOB_QUEUE=tutorial,PROJECT=UESM0016 --force

Build and submit:

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

When the run is completed, look into the archive directory for: g.GW_JRA.TL319_t233_wg37.003.

cd /glade/derecho/scratch/$user/archive/g.GW_JRA.TL319_t233_wg37.003/ocn/hist
ls 

Test your understanding

• What are the impacts of increased zonal wind stress?

• Where do you think the impacts would be largest in the ocean?

• How do you think the changes would compare if you increased meridional wind stress?