Sensitivity of the Global Ocean Circulation to Parameterizations of Mesoscale Tracer Transports

Abstract

The isopycnal transport parameterization of Gent and Mc Williams has been implemented in the GFDL ocean general circulation model, replacing the physically unjustifiable horizontal mixing of tracers. The effects of this parameterization are investigated in a global domain. A comparison of its results with those of the conventional horizontal diffusion shows substantial and significant improvements in several climatically important aspects of the ocean circulation. These improvements include a sharper main thermocline, cooler abyssal ocean, elimination of the Deacon cell as a tracer transport agent, zonally integrated meridional heat transport and surface heat fluxes in better agreement with observations, and better confinement of the locations where deep convection occurs. The sensitivity of the model to the magnitude of the horizontal and isopycnal diffusion coefficients is also studied, showing that the domain averages of potential temperature and salinity, the mass transport of the Antarctic Circumpolar Current, and the meridional mass transport in the Northern Hemisphere all increase with decreasing diffusivity. The northward heat and freshwater transports also reveal significant sensitivities to these coefficients. In addition, the effects of spatially and temporally varying transport and of unequal values of the eddy-induced transport and isopycnal diffusion coefficients are examined.