Attributing Variability in Atlantic Meridional Overturning to Wind and Buoyancy Forcing

Thursday, 18 December 2014: 8:30 AM
David Philip Marshall1, Helen R Pillar2, Patrick Heimbach3 and Helen Louise Johnson1, (1)University of Oxford, Oxford, United Kingdom, (2)Niels Bohr Institute - University of Copenhagen, Copenhagen, Denmark, (3)Massachusetts Institute of Technology, Cambridge, MA, United States
An adjoint model is used to attribute variability in the Atlantic Meridional Overturning Circulation (AMOC) to wind and buoyancy forcing over the preceding 15 years. AMOC variability of magnitude ±5 Sv is excited by local wind forcing. In contrast, interannual to decadal AMOC variability of similar amplitude is excited by heat fluxes in the subpolar North Atlantic, with freshwater fluxes playing a very minor role. The magnitude of the reconstructed AMOC variability does not converge as the time window over which past forcing is accounted for is increased to 15 years. Beyond this point the assumption of linearity may break down, suggesting not all of the observed AMOC variability can be attributed in a linear manner to surface forcing. Nevertheless, the reconstructed AMOC variability is broadly consistent with RAPID observations at 26.5N, especially in periods dominated by wind forcing.