Modeled Global Climate Data from the CSIRO Global Coupled Ocean-Atmosphere-Sea-Ice Model (CSIRO-Mk2 Coupled)

Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO), Climate Research Program is Australia's largest and most comprehensive program investigating the greenhouse effect and global climate change. CSIRO has participated in the climate change scenario experiments of the International Panel on Climate Change (IPCC) using a model called CSIRO Global Coupled Ocean-Atmosphere-Sea-Ice Model (CSIRO-Mk2 coupled).

The CSIRO-Mk2 coupled model is best described by Gordon and O'Farrell (1997). The version used here includes the GM ocean mixing scheme described by Hirst et al (1996). The CSIRO-Mk2 coupled model involves global atmospheric, oceanic, sea-ice and biospheric sub-models (Hirst et al., 1996). The atmospheric, biospheric and sea-ice sub-models are the same as those used in the CSIRO Mark 2 GCM. There is a diagnostic cloud scheme. The model is fully flux corrected. Atmospheric and oceanic components use a spectral R21 horizontal grid (each gridbox measuring about 625 km by 350 km) with 9 vertical levels in the atmosphere and 21 levels in the ocean. The ocean model has a heat transport scheme which significantly reduces problems associated with excessive mixing in the Southern Ocean. On a CRAY YMP computer, climate variables for one model day take 60 seconds to evaluate, so a 10 year run takes 61 hours.

Coupling the atmosphere to the ocean is technically challenging because the ocean has a much longer timescale of variability than the atmosphere. The coupled model requires adjustments to the fluxes of heat, salinity and wind stress which link the atmospheric and oceanic components. Adjusting the heat fluxes at the ocean/atmosphere/ice interface is performed by running the ocean and atmosphere models independently and computing (i) the fluxes required by the ocean model when driven by observed SST, sea-surface surface salinity (SSS) and wind stress, and (ii) the heat fluxes generated by the atmosphere/ice model with observed SST and SSS. The flux adjustment is the difference between (i) and (ii). These adjustments were used in the fully coupled model which generates its own SST, SSS and wind stress.

When flux adjustments are applied in the coupled experiment with present levels of CO2, small errors in the ocean model remain. These errors lead to a drift in climate rather than equilibrium. Additional adjustments were made to the model-generated SST to reduce climatic drift and this resulted in negligible drift in global average SST in the control run. The same flux adjustments are applied to the transient CO2 run, which places an artificial constraint on the variability of sea-surface temperature as the climate changes. This limitation may have important implications for ocean behaviour and atmospheric circulation patterns. (NOTE: CSIRO has recently developed the Mk3 Climate System Model. The major aim in the development of the Mk3 climate model has been to provide a coupled atmosphere-ocean system that gives a significantly improved representation of the current climate relative to the prior model generations. See Gordon et al., 2002 for a full history of the development path of the Mk3 model).

The Mk2 model has been used in a large number of climate-related experiments, and for multi-seasonal predictions. Results from Mk2 Runs based on the IPCC- IS92a (or similar) emmission scenarios and IPCC-SRES scenarios (i.e., IPCC Special Report on Emissions Scenarios data set) have been widely distributed by the IPCC Data Distribution Centre (DDC) (see Download Data Set Links and Dix et al., 2001). Data from other experiments have been distributed by the Climate Impact Group of CSIRO (see Hennessy, 1998). Information on more recent data sets can be obtained from Dr. Roger Jones ([e-mail]).

References:

Charlson, R. J., J. Langner, H. Rohde, C. B. Leovy, and S. G. Warren. 1991. Perturbation of the Northern Hemisphere radiative balance by backscattering from anthropogenic sulfate aerosols. Tellus, 43AB, 152-163.

Dix, M.R., T.I. Elliott, and B.G. Hunt. 2001. Simulations of Climatic Change Based on the Mark 2 CSIRO Coupled Global Climatic Model Using the SRES Scenarios with Sulphate Aerosols. Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia.

Gordon, H. B., and S. P. O'Farrell. 1997. Transient climate change in the CSIRO coupled model with dynamic sea ice. Mon. Wea. Rev., 125, 875-907.

Gordon, H.B., L.D. Rotstayn, J.L. McGregor, M.R. Dix, E.A. Kowalczyk, S.P. O’Farrell, L.J. Waterman, A.C. Hirst, S.G. Wilson, M.A. Collier, I.G. Watterson, and T.I. Elliott. 2002. The CSIRO Mk3 Climate System Model. CSIRO Atmospheric Research Technical Paper No. 60. Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia.

Hennessy, Kevin J. 1998. Climate Change Output. CSIRO Atmospheric Research Technical Paper No. 37. Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia.

Hirst, A. C., H. B. Gordon, and S. P. O'Farrell. 1996. Global warming in a coupled climate model including oceanic eddy-induced advection. Geophys. Res. Lett., 23, 3361-3364.

Kiehl, J. T., and B. P. Briegleb. 1993. The relative roles of sulfate aerosols and greenhouse gases in climate forcing. Science, 260, 311-314.

Mitchell, J. F. B., and T. C. Johns. 1997. On modification of global warming by sulfate aerosols. J. Climate, 10, 245-267.