GFDL CM2.X

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GFDL CM2.X (Geophysical Fluid Dynamics Laboratory Coupled Model, version 2.X) is a coupled atmosphere-ocean general circulation model (AOGCM) developed at the NOAA Geophysical Fluid Dynamics Laboratory in the United States. It is one of the leading climate models used in the Fourth Assessment Report of the IPCC, along with models developed at the Max Planck Institute for Climate Research, the Hadley Centre and the National Center for Atmospheric Research. The solutions of these GFDL CM2 models are described in a series of papers published in the Journal of Climate in 2006.

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[edit] Model construction

Atmosphere

The atmospheric component of the CM2.X models is a 24-level atmosphere run at a resolution of 2 degrees in the east-west and 2.5 degrees in the north-south direction. This resolution is sufficient to resolve the large mid-latitude cyclones responsible for weather variability. It is too coarse, however, to resolve processes such as hurricanes or intense thunderstorm outbreaks.

Ocean

The ocean component is a 50 level ocean, run at a resolution of 1 degree in the east-west direction and varying in the north-south direction from 1 degree in the polar regions to 1/3 of a degree along the equator. This resolution is sufficient to resolve the equatorial current system, but is too coarse to capure the highly energetic mesoscale eddies.

[edit] Simulation description

Two sets of models were run for the IPCC, consisting of very similar ocean circulations but different methodology for solving the equations of motion. The result is that the models have very different wind stresses over the Southern Ocean, with the CM2.0 exhibiting the common bias of winds that are shifted equatorward but the CM2.1 model being one of the few that have winds close to the correct latitude and magnitude in this region (Russell et al., 2006). Work by Reichler and Kim at the University of Utah suggests that this model series is one of the top models in a range of atmospheric characteristics. It also has one of the better simulations of El Nino among the IPCC models (van Oldenburgh et al., 2005; Wittenberg et al., 2006). However, as is the case with most AOGCMs run without flux adjustment, the models fail to capture the cold upwelling zones along the eastern boundaries of the Pacific and Atlantic, and tend to produce an overly dry Amazon basin.

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[edit] References

  • Delworth, T. et al., (2006) GFDL's CM2 global coupled climate models- Part 1: Formulation and simulation characteristics, Journal of Climate, 19, 643-674. [1]
  • Gnanadesikan A., et al., (2006) GFDL's CM2 global coupled climate models- Part 2: The baseline ocean simulation, J. Climate, 19, 675-697. [2]
  • Knutson, T. et al., (2006), Assessment of Twentieth Century Regional Surface Temperature Trends using the GFDL CM2 Coupled Models, Journal of Climate, 19, 1624-1651.[3]
  • Russell, J.L., R.J. Stouffer and K.W. Dixon (2006), Intercomparison of the Southern Ocean circulation in IPCC coupled model control simulations. Journal of Climate, 19(18), 4560-4575.[4]
  • van Oldenburgh,G., S.Y. Philip and M. Collins (2005), El Nino in a changing climate- a multi-model study, Ocean Science 1,81-95. [5]
  • Wittenberg, A., et al. (2006), GFDL's CM2 global coupled climate models- Part 3: Tropical Pacific Climate and ENSO, Journal of Climate, 19, 675-697. [6]
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