EDDY PARAMETRIZATION AND THE OCEANIC RESPONSE TO IDEALIZED GLOBAL WARMING

A coarse-grid global ocean general circulation model (OGCM) is used to determine the role of sub-grid scale eddy parametrization schemes in the response to idealized changes in the surface heat flux, of the sam e order as expected under increased atmospheric CO2 concentrations. Tw o schemes are employed. The first (H) incorporates standard horizontal mixing, whereas the second (G) combines both enhanced isopycnal mixin g and eddy-induced transport. Uniform surface heating anomalies of + 2 Wm(-2) and - 2Wm(-2) are applied for 50 years, and the results are com pared with a control experiment in which no anomalous heating is impos ed. A passive ''heat'' tracer is applied uniformly (at a rate of 2Wm(- 2) for 50 years) in a separate experiment. The sea-surface temperature response to global surface heating is generally larger in G, especial ly in the northern subtropical gyres, along the southern coast of Aust ralia and off the Antarctic coast. A pronounced interhemispheric asymm etry (primarily arising from an anomalous response south of 35 degrees S) is evident in both H and G. The surface trapping of passive tracer s in the Southern Hemisphere is generally greater in G than it is in H , and is particularly pronounced along the prime meridian (0 degrees E ). Dynamical changes (i.e., changes in horizontal and vertical current s, convection, and preferred mixing: and eddy transport pathways) enha nce surface warming in the tropics and subtropics in both G and H. The y are dominated by an anomalous meridional overturning centred on the equator, which may also operate in greenhouse warming experiments usin g coupled atmosphere-ocean GCMs. Over the Southern Ocean the passive t racer experiments and associated ventilation rates suggest that surfac e warming will be greater in G than in H. In fact, the contrast betwee n the dynamical responses evident in G and H in the actual heating exp eriments leads to a situation in which the reverse is often true. Over all, dynamical changes enhance the interhemispheric assymetry, more so in G than in H.