MOM3 relative to MOM2 The main advances in MOM3 relative to MOM2 are in the physics, numerics, and parallelization. The following is a brief outline of the changes.
KPP vertical mixing scheme of Large, McWilliams, and Doney (1994).
Partial bottom cell topography of Pacanowski and Gnanadesikan (1998).
Bottom boundary layer scheme of Gnanadesikan.
The Gent-McWilliams skew-flux of Griffies (1998).
Generalization of the isoneutral diffusion scheme of Griffies et al. to allow for partial bottom cells.
Streamlining of the isoneutral mixing schemes which results in a reduction in model run time relative to the MOM2 implementation.
The Held and Larichev (1996) and Visbeck, Marshall, Haine, and Spall (1997) closures for the Redi and GM tracer diffusivities.
The Roberts and Marshall (1998) biharmonic mixing scheme.
The explicit free surface of Griffies et al (2000).
Fresh water fluxes into the explicit free surface rather than virtual salt fluxes.
A specified spatially variable horizontal viscosity which includes the proper kinematic terms proportional to the spatial derivatives of the viscosity.
The biharmonic Smagorinsky scheme of Griffies and Hallberg (2000).
The meridional streamfunction diagnostic has been expanded so that the streamfunction can be computed using potential density as a vertical coordinate.
A diagnostic to map all the terms affecting the evolution of locally referenced potential density
The old time manager has been replaced by a Fortran 90 time manager which defines time structures and overloads the standard numerical operations of plus, minus, times, and divide to work with structures. All manipulations involving time are now much simpler than before.
Common blocks are being replaced by Fortran 90 modules. (For the barotropic portion only. There is a 30% slow down in speed when common blocks are removed from the baroclinic and tracer portions of the model.
In addition to the Euler Backward and the forward mixing time steps every nmix time steps (usually nmix = 17), an option has been added for a Robert filter applied every time step.
The model topography can now be changed by editing the file kmt.dta with a text editor.
An option for a square grid (one where Delta y compensates for the convergence of meridians to keep the grid cells square.
The test case resolution has been changed from a 4 x 3 grid to a 3 x 2.765 grid to facilitate parallel processing tests with up to 64 processors.
The model mean radius of the earth has been changed from 6370 km to 6371 km.
A parameterization for mixing tracers between unconnected regions of ocean has been added as a way to handle the tracer exchange between the Mediterranean and Atlantic, as well as other regions where resolution is insufficient to allow realistic exchanges.
The older relaxation methods for solving elliptic equations have been removed in favor of the method of conjugate gradients.