Oceanic overturning and heat transport: The role of background diffusivity

AbstractThe role of oceanic background diapycnal diffusion for the equilibrium climate state is investigated in the coupled climate model CM2G. Special emphasis is put on the oceanic meridional overturning and heat transport. Six runs with the model, differing only by their value of the background diffusivity, are run to steady state and the statistically steady integrations are compared. The diffusivity changes have large scale impacts on many aspects on the climate system. Two examples are the volume mean potential temperature that increases by 3.6 °C between the least and most diffusive run and the Antarctic sea ice extent, which reduces rapidly as the diffusivity increases. The overturning scaling with diffusivity is found to agree rather well with classical theoretical results for the upper but not for the lower cell. An alternative empirical scaling with the mixing energy is found to give good results for both cells. The oceanic meridional heat transport increases strongly with the diffusivity, an i...