Dependency of simulated tropical Atlantic current variability on the wind forcing

Abstract. The upper wind-driven circulation in the tropical Atlantic Ocean plays a key role in the basin wide distribution of water mass properties and affects the transport of heat, freshwater, and biogeochemical tracers such as oxygen or nutrients. It is crucial to improve our understanding of its long-term variability which largely relies on model simulations due to sparse observational data coverage especially before the mid-2000s. We applied two different forcing products to a high-resolution ocean model which resolves the complex zonal current field in the tropical Atlantic. Where possible, we compared the simulated results to long-term observations. We found that in simulations the strength of the wind stress curl above the upwelling regions of the eastern tropical North Atlantic is important to set the mean strength of the off-equatorial surface and subsurface currents north of the equator. Too strong wind stress curl above the upwelling regions seems to overestimate the subsurface currents resulting in unrealistic seasonal variability. The simulated decadal to multidecadal variability of the tropical Atlantic current field can, to a large extent, be explained by changes in the Sverdrup dynamics. The combination of both simulations and observations reveals that the recent strengthening of the EUC can be indeed interpreted as a recovery from a weak phase the current experienced since the late 1990s. Where it has become common place for models to explain processes behind ocean observations, we postulate that long-term observations, once they have reached a critical length, can be used to test the quality of wind-driven simulations. This study presents one step in this direction.