Decadal variability of shallow cells and equatorial sea surface temperature in a numerical model of the Atlantic

Abstract

The relative role of extraequatorial mechanisms modulating decadal sea surface temperature anomalies (SSTA) in the equatorial Atlantic is investigated using a suite of sensitivity experiments based on an ocean general circulation model. The model is forced by observed wind stress and/or computed heat flux from an associated advective atmospheric mixed layer model. In addition, the surface forcing is optionally applied on the equator or in off‐equatorial regions. The long‐term response of equatorial SST is dominated by local forcing. However, a weak but significant part of the response that is not in phase with the locally induced SST variability is caused by remote forcing. Subtropical cells (STCs) provide the oceanic bridging of the climate signals. The dynamical forcing leads to a spin‐up and spin‐down of the shallow cells, which, in the case of local forcing included, coincides with cold and warm SSTA. The local heat flux forcing reveals an overall damping tendency on the dynamical SST response. When excluding the local forcing, the isolation of the effect of the northern remote forcing from the one in the south appears to be essential in understanding the respective mechanisms at work. In the Northern Hemisphere, the spin‐up and spin‐down of the STC is highly correlated with the (lagging) SSTA, and the effect of off‐equatorial heat flux forcing on SSTA is negligible. In the Southern Hemisphere, both momentum and heat fluxes in the subtropics lead to a significant SST response on the equator.