AbstractThe Atlantic Multidecadal Oscillation (AMO) is the leading mode of Atlantic Sea Surface Temperature (SST) variability at multidecadal time-scales. Previous studies have denoted that AMO could modulate El Niño-Southern Oscillation (ENSO) variance. However, the role played by AMO in the Tropical Atlantic Variability (TAV) is still uncertain. Here, it is demonstrated that during negative AMO phases, associated with a shallower thermocline, the eastern equatorial Atlantic SST variability is enhanced by more than 150% in boreal summer. Consequently, the inter-annual TAV modes are modified. During negative AMO, the Atlantic Niño displays larger amplitude and a westward extension and it is preceded by a simultaneous weakening of both Subtropical Highs in winter-spring. In contrast, a meridional seesaw SLP pattern evolving into a zonal gradient, leads the Atlantic Niño during positive AMO. The North Tropical Atlantic (NTA) mode is related to a Scandinavian blocking pattern during winter-spring in negative AMO, while under positive AMO it is part of the SST-tripole associated with the North Atlantic Oscillation. Interestingly, the emergence of an overlooked variability mode, denoted as Horse-Shoe (HS) pattern, is favored during negative AMO. This anomalous warm (cool) HS surrounding an eastern equatorial cooling (warming) is remotely forced by an ENSO phenomenon. During negative AMO, the tropical-extratropical teleconnections are enhanced and the Walker circulation is altered. This, together with the increased equatorial SST variability, could promote the ENSO impacts on TAV. Our results give a step forward in the better understanding of TAV, which is essential to improve its modelling, impacts and predictability.
Journal of Climate – American Meteorological Society
Published: Jun 28, 2017
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