Decadal variability of the midlatitude climate system driven by the ocean circulation

A midlatitude coupled ocean–atmosphere model is used to investigate interactions between the atmosphere and the wind-driven ocean circulation. This model uses idealized geometry, yet rich and complicated dynamic flow regimes arise in the ocean due to the explicit simulation of geostrophic turbulence. An interdecadal mode of intrinsic ocean variability is found, and this mode projects onto existing atmospheric modes of variability, thereby controlling the time scale of the atmospheric modes. It is also shown that ocean circulation controls the time scale of the SST response to wind forcing, and that coupled feedback mechanisms thus modify variability of the atmospheric circulation. It is concluded that ocean–atmosphere coupling in the midlatitudes is unlikely to produce new modes of variability but may control the temporal behavior of modes that exist in uncoupled systems.