A three dimensional ocean model with an idealized global geometry and coarse resolution is coupled to a two dimensional (zonal-mean) statistical-dynamical atmospheric model and a simple thermodynamic sea ice model. Long term present-day climate simulations have been carried out with and without flux adjustments. The results of these simulations agree in general with the results of similar simulations with more sophisticated coupled Atmosphere Ocean GCMs. A drift of the climate in the simulation without flux adjustments is caused mainly by the mismatch in the heat transports by the two models. The model is used to test the possibility of using asynchronous integrations of the tracer and momentum equations. The results show that this is feasible, so long as the tracer time step is no more than about 12 times the momentum time step.
The model is being used to determine what factors are important in controlling the thermohaline circulation and its sensitivity to climate change. Results of recent simulations with ocean GCMs show that produced distribution of CFC11 agrees better with observations when Gent-McWilliams (GM) parameterization scheme is used. In particular, models which use horizontal diffusion (HD) tend to overestimate depth of CFC11 penetration into the deep ocean in the high latitudes of the Southern Hemisphere. To test dependence of the model response to external forcing on the parameterization of mesoscale eddies, we carry out two experiments in which atmospheric CO2 increases 1% per year, one with each of the parameterizations. In the one with HD, the warming and its pattern is qualitatively similar to that in published experiments with coupled GCMs (which also use HD). However in the simulation with GM the zone of deep heat penetration in the southern ocean is absent. As a result there is very little inter-hemispheric asymmetry in the surface warming, in contrast to all published global warming simulations with coupled GCMs. The use of GM parameterization also results in substantially larger surface warming.
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12th Conference on Atmospheric and Oceanic Fluid Dynamics