GFDL - Geophysical Fluid Dynamics Laboratory

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Ocean models at GFDL

Schematic of processes that can affect ocean circulation.The Oceans and Climate Group at GFDL includes the lead developers of three of the leading ocean models used for climate studies:
  • The Modular Ocean Model v4.1 (MOM4) a B-grid level coordinate model whose development has been headed by Stephen Griffies.
  • The MIT Ocean General Circulation model (MITGCM) a C-grid level-coordinate whose development has been headed by Alistair Adcroft.
  • The Generalized Ocean Layer Dynamics model (GOLD), a descendant of the isopycnal (density-coordinate) HIM model whose development has been headed by Robert Hallberg.

All of these models break the ocean up into boxes, and represent the exchange of tracers and momentum between these boxes using the primitive equations for fluid flow on a sphere. While the models all start with the same continuous equations, the discrete forms of the equations (translated to the box scale) are different. Different parts of the ocean are most naturally represented using different coordinate systems. Level-coordinate models like MOM and MITGCM in which each box is at the same level are numerically easy to code, and have been the dominant class of model used for climate studies. Such models may also have particular advantages in representing the transition between the poorly stratified mixed layer and the interior ocean where flow is predominantly along density surfaces. Isopycnal models like GOLD handle the interior ocean more naturally, and may also have significant advantages in representing thin overflows. In shallow coastal regions, where the top and bottom boundary layers are thought to be most important, many oceanographers use terrain-following coordinate systems. For more discussion, see this paper by Griffies et al.

Important development in the past few years include:

The development of generalizable code that can be run using multiple vertical coordinates (illustrated in the figure above).

The development of a new discretization for the representation of the pressure gradient, that significant reduces spurious errors in isopyncal models arising from the nonlinearity of the equation of state.

Development of the ability to model flow under ice shelves.

Scientists involved in this work:

Alistair Adcroft (MITGCM, GOLD, numerical representation of physics in different vertical coordinates)
Anand Gnanadesikan (model diagnostics, flow under ice shelves, physical parameterizations)
Stephen Griffies (MOM, level-coordinate models)
Robert Hallberg (HIM, GOLD, isopycnal coordinate modeling)
Matt Harrison (physical parameterizations, model diagnostics, MOM/GOLD development)
Chris Little (flow under ice shelves)

Links

Ocean model development team home page.

CM2M and CM2G coupled climate models.

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