The rationale for the Large Scale Geostrophic Ocean general circulation model (LSG-OGCM) is based on the observation that for a large scale ocean circulation model designed for climate studies, the relevant characteristic spatial scales are large compared with the internal Rossby radius throughout most of the ocean, while the characteristic time scales are large compared with the periods of gravity modes and barotropic Rossby wave modes. In the present version of the model, the fast modes have been filtered out by a conventional technique of integrating the full primitive equations, including all terms except the nonlinear advection of momentum, by an implicit time integration method. The free surface is also treated prognostically, without invoking a rigid lid approximation. The numerical scheme is unconditionally stable and has the additional advantage that it can be applied uniformly to the entire globe, including the equatiorial and coastal current regions.
Maier-Reimer, E., and U. Mikolajewicz
(1992): The Hamburg Large Scale Geostrophic Ocean General Circulation Model
(Cycle 1); Technical Report No.2 of Deutsches Klimarechenzentrum.
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S.S. Drijfhout, E. Maier-Reimer, U. Mikolajewicz
Royal Netherlands Meteorological Institute, P.O. Box 201, De Bilt, 3730AE, The Netherlands
1996: JGR-Oceans, Vol. 101, No. C10 , p. 22,563
The flow which constitutes the conveyor belt in the Hamburg LSG OGCM has been investigated with the help of a particle tracking method. In the region of NADW formation, a thousand trajectories were calculated backward in time to the point where they upwell from the deep ocean. In the Atlantic Ocean the path and strength (17 Sv) of the conveyor belt in the model are found to be consistent with observations. All trajectories enter the South Atlantic via Drake Passage, as the model does not simulate any Agulhas leakage. Large changes in water masses occur in the South Atlantic midlatitudes and subtropical North Atlantic. Along its path in the Atlantic, the water in the conveyor belt is transformed from Antarctic Intermediate Water to Central North Atlantic Water. The ventilation of thermocline waters in the South Atlantic midlatitudes is overestimated in the model due to too much convective deepening of the winter mixed layer. As a result, the fraction of the conveyor belt water flowing in the surface layer is also overestimated, along with integrated effects of atmospheric forcing. The abnormally strong water mass transformation in the South Atlantic might be related to the absence of Agulhas leakage in the model.