Studies of the ocean-atmosphere system using a coupled climate model

An idealized atmospheric model consisting of energy and moisture conservation equations is developed for studies of the ocean's role in climate. Testing under fixed oceanic conditions yields a climatology comparable with direct observations, as does the case when the interpentadal (1955–59; 1970–74) sea surface temperature fields are applied.; The atmospheric model is then coupled to an ocean general circulation model as well as a thermodynamic ice model without the use of flux adjustments. When configured for a global realistic geometry, the model faithfully represents deep water formation in the Atlantic and Southern Oceans with upwelling throughout the Pacific and Indian Oceans. The model is then utilized to investigate the influence of meltwater discharge on the stability of North Atlantic Deep Water (NADW) production and the Younger Dryas (YD ∼ 14ka). Results suggest pre-YD meltwater is capable of diminishing NADW to the point where diversion of meltwater from the Gulf of Mexico to the St. Lawrence completely inhibits its production. The coupled model appears to be stable in this state, equivalent to the “Southern Sinking” equilibrium identified in previous models. Inclusion of the wind stress/speed feedback, however, has a dramatic effect causing a reestablishment of NADW production.; The model is then configured in a four basin-two hemisphere sector geometry, crudely representative of the global oceans. Two identically formulated models (one of which employs flux adjustments) are then perturbed to assess the role of flux adjustments on the ocean's response to a “global warming-like” scenario. Significant global and basin-scale differences exist between the cases which is linked to the influence of the salt-flux adjustment on the overturning cells within the model Atlantic and Southern Oceans. Results further suggest that minimizing the coupling shock prior to applying the perturbation leads to results slightly closer between the models, although large differences still persist.; The model is then configured for a highly idealized 60° sector geometry to study the influence of horizontal resolution and parameterized eddy processes on poleward heat transport. As resolution increases, the total oceanic heat transport steadily increases. This result is also evidenced in a parallel series of ocean-only model studies driven by restoring boundary conditions. In each case the increase in heat transport is associated with the steady currents. In particular the baroclinic gyre transport (our model analog of the transport associated with the “Warm Core” jet region of the Gulf Stream) increases by a factor of 5 between coarsest and finest resolution.; Spontaneous decadal-scale variability is also found to exist in the higher resolution experiments (with the exception of one of the restoring cases). The oscillation is thermally driven by an advective-convective mechanism and linked to the value of the horizontal diffusivity employed. Increasing the diffusivity in the high resolution cases is enough to destroy the variability, while decreasing the diffusivity in the moderately coarse resolution case is enough to induce the variability. These results point to the importance of higher resolution in the oceanic component of current climate models, yielding enhanced poleward heat transports and revealing the existence of richer decadal-scale variability in models which require less parameterized viscosity and diffusion.