2004 LOM Workshop Monday 11:10 - 11:30 a.m.
A Global Ocean Model Based on Icosahedral-Hexagonal Grids With a Hybrid Vertical Coordinate
Todd Ringler, David Randall, John Baumgardner, Don Stark, Bert Semtner
Colorado State University
todd@atmos.colostate.edu
ABSTRACT
This talk will present results from a new global ocean general circulation model (OGCM). The ocean model uses an icosahedral-hexagonal grid to tile the surface of the sphere and hybrid (floating) coordinates to discretize the vertical depth of the ocean. The use of icosahedral-hexagonal grids leads to a highly uniform and isotropic discretization of the sphere and eliminates problematic grid singularities found in other grid systems. The hybrid coordinate used to discretize the vertical direction spans the limits between an Lagrangian-coordinate, such as isopycnal coordinates, and an Eulerian-coordinate, such as z-level coordinates. As a result, the model can be integrated forward in time for several days using Lagrangian vertical coordinates to minimize vertical diffusion and dispersion. At fixed time intervals, the vertical layers are mapped back to z-level coordinates and the integration continues forward in time. This type of coordinate is referred to as an Arbitrary Lagrangian Eulerian coordinate and is being developed at LANL. The model contains much of the functionality of a full production ocean model including convective adjustment, implicit vertical mixing, UNESCO equation of state, realistic bathymetry, and sub-grid scale mixing parameterizations. The results show realistic ocean circulations using 40962 grids cells in the horizontal (nominal 1 degree grid) and 33 layers in the vertical. The ocean is forced using monthly mean NCEP wind stresses and restoring to Levitus temperature and salinity in the top 5 meter layer. The results demonstrate that not only is this a viable approach to ocean modeling, but also provides an alternative approach to overcome many of the classical problems in ocean modeling.
LOM Users' Workshop, February 9-11, 2004