Dynamics of the Atlantic meridional overturning circulation. Part 2: Forcing by winds and buoyancy

Solutions forced by τx and ρ∗ differ markedly from those forced only by ρ∗ because water flows across y2 throughout the interior of the Subpolar Gyre, not just near the eastern boundary. In some of our solutions, the strength of the MOC's descending branch is determined entirely by this wind-driven mechanism, whereas in others it is also affected by Rossby-wave damping near the eastern boundary. Upwelling can occur in the interior of the Subpolar Gyre and in the western-boundary layer, providing “shortcuts” for the overturning circulation; consequently, there are different rates for the convergence of upper-layer water near y2,Mn, and the export of deep water south of the Subpolar Gyre, M, the latter being a better measure of large-scale MOC strength. When western-boundary upwelling occurs in our solutions, M is independent of the diapycnal processes in the subpolar ocean.