Local and remote wind stress forcing of the seasonal variability of the Atlantic Meridional Overturning Circulation (AMOC) transport at 26.5N

Abstract

The transport of the Atlantic Meridional Overturning Circulation (AMOC) varies considerably on the seasonal time scale at 26.5N, according to observations made at the RAPID-MOCHA array. Previous studies indicate that the local wind stress at 26.5N, especially a large wind stress curl at the African coast, is the leading contributor to this seasonal variability. The purpose of the present study is to examine whether nonlocal wind stress forcing, i.e., remote forcing from latitudes away from 26.5N, affects the seasonal AMOC variability at the RAPID-MOCHA array. Our tool is a two-layer and wind-driven model with a realistic topography and an observation-derived wind stress. The seasonal cycle of the modeled AMOC transport agrees well with RAPID-MOCHA observations while the amplitude is in the lower end of the observational range. In contrast to previous studies, the seasonal AMOC variability at 26.5N is not primarily forced by the wind stress curl at the eastern boundary, but is a result of a basin-wide adjustment of ocean circulation to seasonal changes in wind stress. Both the amplitude and phase of the seasonal cycle at 26.5N are strongly influenced by wind stress forcing from other latitudes, especially from the subpolar North Atlantic. The seasonal variability of the AMOC transport at 26.5N is due to the seasonal redistribution of the water mass volume and is driven by both local and remote wind stress. Barotropic processes make significant contributions to the seasonal AMOC variability through topography-gyre interactions.