A wind-driven perspective on the Atlantic Meridional Overturning Modelling eddy induced deep layer transport with HIM

Abstract

With the Meridional Overturning Circulation (MOC) it is considered that a large part of the deep ocean transport is buoyancy driven. Several studies however have shown that the deep ocean transport shows a circulation structure that cannot be explained by the buoyancy forcing alone. This structure is due to eddies that drive the deep ocean. Eddies are the result of wind forcing which in the first place drive the surface gyres, but also create instability which induces transport of energy to the deep ocean. In this study the effect of the wind induced eddy kinetic energy is studied by modeling with the Hallberg Isopycnal Model (HIM) in order to analyse the effect on the deep ocean transport and the MOC. The model consists of a simplified ocean with a rectangular domain and two layers with a density difference. The only forcing on the domain is the wind forcing so the buoyancy forcing is not implemented in the model. The results show for both the surface and deep layer a transport induced by the wind at surface. Whether these results can explain elements of the MOC is further analysed by a tracer analysis. In addition the model results are compared with measurements conducted over the 26,5oN “Rapid” array. At this array the MOC is calculated by the summation of the Gulf Stream transport, Ekman transport and mid-ocean transport. The comparison gives an interesting result and raises the question whether the Ekman transport should be taken into account in determining the MOC from Rapid.