Oceanic control of multidecadal variability in the North Atlantic.

Thierry Huck, Olivier Arzel, Alain Colin de Verdière, Florian Sévellec, Quentin Jamet 

The origin of multidecadal variability in the North Atlantic ("AMO, "AMV") has not yet been settled, and a wide range of hypothesis have been proposed in various coupled model simulations but none allow a straightforward comparison or validation with (maybe too short) observations.
On the other hand, multidecadal variability appears spontaneously in idealized ocean simulations forced by prescribed surface buoyancy flux, through baroclinically-unstable Rossby waves. Such mechanism was also found in more realistic North Atlantic configurations (OPA ORCA2°), with and without eddies, with and without atmospheric coupling. The signature of this mode in the more realistic simulations is comparable to the signature of the AMO in the observations, as far as it can be identified and distinguished from global warming.
We review several results from the most idealized studies to the more realistic in ocean and coupled GCMs to support the relevance of such a mechanism for the Atlantic Multidecadal Oscillation.