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The Third Generation Coupled Global Climate Model

Canadian Centre for Climate Modelling and Analysis

The third version of the Canadian Centre for Climate Modelling and Analysis (CCCma) Coupled Global Climate Model (CGCM3), makes use of the same ocean component as that used in the earlier The Second Generation Coupled Global Climate Model, but it makes use of the substantially updated atmospheric component The Third Generation Atmospheric General Circulation Model. More details regarding the atmospheric component can be found by clicking on this link. The ocean component is describe in detail in Flato and Boer (2001), Kim et al. (2002, 2003), and references therein. The sea-ice component is a two-category model (mean thickness and concentration) with cavitating fluid dynamics (Flato and Hibler, 1992) and thermodynamics as in The First Generation Coupled Global Climate Model and The Second Generation Coupled Global Climate Model, except that a prognostic equation for ice concentration is included following Hibler (1979).

The initial version of CGCM3 was developed and ran on a NEC SX/6 vector supercomputer. A subsequent version, CGCM3.1, incorporates changes required to run efficiently on a new distributed memory IBM computer system. This latter version is the one used to produce an extensive suite of model simulations for use in the IPCC Fourth Assessment Report.

CGCM3.1 is run at two different resolutions. The T47 version has a surface grid whose spatial resolotion is roughly 3.75 degrees lat/lon and 31 levels in the vertical. The ocean grid shares the same land mask as the atmsosphere, but has four ocean grid cells underlying every atmospheric grid cell. The ocean resolution in this case is roughly 1.85 degrees, with 29 levels in the vertical.

The T63 version has a surface grid whose spatial resolution is roughly 2.8 degrees lat/lon and 31 levels in the vertical. As before the ocean grid shares the same land mask as the atmosphere, but in this case there are 6 ocean grids underlying every atmospheric grid cell. The ocean resolution is therefore approximately 1.4 degrees in longitude and 0.94 degrees in latitude. This provides slightly better resolution of zonal currents in the Tropics, more nearly isotropic resolution at mid latitudes, and somewhat reduced probles with converging meridians in the Arctic.

Acknowledgements

The development of CGCM3 was a team effort involving G. Flato, G. Boer, D.Y. Robitaille, W.G. Lee, W. Merryfield, and O. Saenko, along with many contributions from the AGCM development team.

References:

Flato, G.M. and G.J. Boer, 2001: Warming Asymmetry in Climate Change Simulations. Geophys. Res. Lett., 28, 195-198.

Flato, G.M. and Hibler, W.D. III, 1992: Modelling Pack Ice as a Cavitating Fluid. J. Phys. Oceanogr., 22, 626-651.

IPCC, 2001: Climate Change 2001: The Scientific Basis. J.T. Houghton et al. (eds.), Cambridge University Press, 881pp.

Kim, S.-J., G.M. Flato, G.J. Boer and N.A. McFarlane, 2002: A coupled climate model simulation of the Last Glacial Maximum, Part 1: transient multi-decadal response. Climate Dynamics, 19, 515-537.

Kim, S.-J., G.M. Flato, G.J. Boer, 2003: A coupled climate model simulation of the Last Glacial Maximum, Part 2: approach to equilibrium Climate Dynamics, 20, 635-661.