Is the decadal variability in the tropical Atlantic a precursor to the NAO?

In the past two decades climate research in the tropical Atlantic with respect to the inter-hemispheric gradient of sea surface temperature (SST) emphasized the predominance of decadal-scale variability. Our results show that this mode of variability is prevalent only for part of the last 130-years record (the 1880s, the 1920s and, especially, the 1970s). There is a lag of a few months between the decadal variations of the inter-hemispheric gradient of SST and the decadal variability of the North Atlantic Oscillation (NAO). This seems to indicate that the 10-year variability first develops in the tropics and then propagates polewards. The inter-hemispheric gradient of SST mode should be thought as episodic and not as a periodic oscillation

Evidence of remote forcing in the Equatorial Atlantic ocean

An analysis of sea-surface temperature (STT) and surface winds in selected areas of the Tropical Atlantic indicates that the nonseasonal variability of SST in the Eastern Equatorial Atlantic (Gulf of Guinea) is highly correlated with the nonseasonal variability of the zonal wind stress in the Western Equatorial Atlantic. A negative (positive) anomaly of the zonal wind stress near the North Brazilian coast is followed by a positive (negative) SST anomaly in the Gulf of Guinea about one month later. Furthermore, the correlation betweenthe local winds stress anomaly and STT anomaly in the Gulf of Guinea is considerably smaller. These preliminary results indicate that remote forcing in the Western Equatorial Atlantic ocean is an important factor affecting the Eastern Equatorial Atlantic sea-surface temperature. Recent equatorial theories are consistent with these observations. (Résumé d'auteur

Multiple causes of interannual sea surface temperature variability in the equatorial Atlantic Ocean

The eastern equatorial Atlantic Ocean is subject to interannual fluctuations of sea surface temperatures, with climatic impacts on the surrounding continents. The dynamic mechanism underlying Atlantic temperature variability is thought to be similar to that of the El Nino/Southern Oscillation (ENSO) in the equatorial Pacific, where air-sea coupling leads to a positive feedback between surface winds in the western basin, sea surface temperature in the eastern basin, and equatorial oceanic heat content. Here we use a suite of observational data, climate reanalysis products, and general circulation model simulations to reassess the factors driving the interannual variability. We show that some of the warm events can not be explained by previously identified equatorial wind stress forcing and ENSO-like dynamics. Instead, these events are driven by a mechanism in which surface wind forcing just north of the equator induces warm ocean temperature anomalies that are subsequently advected toward the equator. We find the surface wind patterns are associated with long-lived subtropical sea surface temperature anomalies and suggest they therefore reflect a link between equatorial and subtropical Atlantic variability