3.3 The MOM Test Cases

MOM is executed by a CRAY T90 script run_mom which is in directory MOM_3 on the workstation side of the file structure. The script executes a test case global domain with a horizontal resolution of $3^\circ$ in longitude by about $2.8^\circ$ in latitude with 15 vertical levels. This yields 122 points in longitude (120 + 2 for cyclic conditions) and 66 latitude rows (64 + 2 for boundary rows which is a useful size for parallel processing tests with up to 64 processors). For simplicity and portability, idealized internally generated geometry (not very accurate) and topography (absolutetly bogus) are used. More realistic data can be easily included by enabling the option for Scripps topography in the run script. Many diagnostics are enabled (to demonstrate that they work) and output is in 32 bit IEEE format. As an alternative, an option for NetCDF formatted output can be enabled within the run script.

Only a very few options are enabled to keep physics simple for the test cases. Basically, an option is enabled for constant vertical mixing. In the horizontal, a variable horizontal mixing parameterization is enabled which weights the constant horizontal viscosity coefficient by the cosine of latitude to compensate for the convergence of meridians. This aids in resolving the Munk boundary layer at each latitude yet keeps the Killworth time step restriction from limiting the time step at high latitudes. When realistic topography is used, a light smoothing of topography is also needed and enabled northward of 85N to reduce topographic slopes so the Killworth condition remains satisfied. Latitudes northward of 75N are filtered with a fourier filter to compensate for time step restrictions due to convergence of meridians.

The barotropic equation is solved by the method of rigid lid stream function although options exist for an implicit and explicit free surface as well. The time steps are asynchronous with 1 day for density and 1 hour for internal and external modes.

Test cases #0, #1, #2, and #3 use various types of surface boundary conditions with the above configuration. They are selected by setting the CASE variable within script run_mom as follows:

• CASE=0 uses idealized surface boundary conditions which are a function of latitude only and independent of time: zonally averaged annual mean Hellerman and Rosenstein (1983) wind stress with surface temperature and salinity damped back to initial conditions on a time scale of 50 days using a thickness of about 25 meters. Initial conditions are no motion and an idealized temperature (function of latitude and depth) and salinity (constant) structure^3.9. All required data is generated internally and therefore the DATABASE is not needed. This is similar to the test case for MOM 1. The results are in file EXP/TEST_CASE/printout.0.gfdl.

• CASE=1 is similar to CASE=0 except uses time mean surface boundary conditions from SBC/TIME_MEAN which are assumed to have been prepared using scripts run_sbc and run_ic in PREP_DATA. These surface boundary conditions are a function of longitude and latitude but independent of time. The results are in file EXP/TEST_CASE/printout.1.gfdl.

• CASE=2 is similar to CASE=0 except uses time varying surface boundary conditions from SBC/MONTHLY as described in Section 3.2 which are assumed to have been prepared using scripts run_sbc and run_ic in PREP_DATA. The surface boundary conditions are linearly interpolated to each time step as the integration proceeds. The results are in file EXP/TEST_CASE/printout.2.gfdl.

• CASE=3 is similar to CASE=0 except uses surface boundary conditions supplied by an idealized atmospheric model as described in Section 3.2. This illustrates coupling MOM to an atmospheric GCM. The results are in file EXP/TEST_CASE/printout.3.gfdl.