Interannual atmospheric variability forced by the deep equatorial Atlantic Ocean

Brandt, Peter; Funk, Andreas; Hormann, Verena; Dengler, Marcus; Greatbatch, Richard John; Toole, John M.

doi:10.1038/nature10013

Cited by 86 publications

(106 citation statements)

References 27 publications

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“…Several studies have demonstrated that even though weaker than in the Pacific, the Bjerknes feedback is active in the equatorial Atlantic [e.g., Zebiak, 1993;Keenlyside and Latif, 2007;Lübbecke and McPhaden, 2013;Deppenmeier et al, 2016]. Other mechanisms that have been discussed involve meridional advection of temperature anomalies [Richter et al, 2013], forcing from equatorial deep jets [Brandt et al, 2011b], and heat flux forcing [Nnamchi et al, 2015]. Despite the differences that exist between ENSO and the Atlantic Niño mode, our working hypothesis, based on several studies like those cited above, is that the Bjerknes feedback plays a central role in the equatorial Atlantic.…”

Section: Introductionmentioning

confidence: 99%

Symmetry of the Atlantic Niño mode

Lübbecke

McPhaden²

2017

Geophysical Research Letters

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El Niño–Southern Oscillation (ENSO) in the Pacific is asymmetric for warm and cold events with respect to amplitude, spatial patterns, and temporal evolution. Here the symmetry of the Atlantic Niño mode, which many previous studies have argued is governed by atmosphere‐ocean dynamics similar to those of ENSO, is investigated using two different ocean reanalysis products. Calculation of Bjerknes feedback terms for the Pacific reveals a pronounced asymmetry between warm and cold events, though unlike most previous studies, the largest asymmetry is found in the relationship between eastern Pacific thermocline depth and sea surface temperature anomalies. For the Atlantic, cold events are effectively mirror images of warm events with Bjerknes feedbacks of similar strength. The analysis supports not only the conclusion that Atlantic Niños are more symmetric than ENSO but also the hypothesis itself that the Bjerknes feedback is operative in the Atlantic given the strength of the relationship between the key variables involved.

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Section: Introductionmentioning

confidence: 99%

Symmetry of the Atlantic Niño mode

Lübbecke

McPhaden²

2017

Geophysical Research Letters

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“…Thus, the tropical Atlantic Ocean is often implicated in climate variability over parts of the adjacent continents including the Guinea coast, the Sahel, and Brazil Nordeste. Studies suggest that during the boreal summer [June-August (JJA)], tropical Atlantic variability is dominated by the equatorial zonal mode termed the Atlantic Niño occurring at the interannual time scale (Zebiak 1993;Chang et al 2006;Keenlyside and Latif 2007;Brandt et al 2011). The peak phase of the Atlantic Niño in JJA is characterized by a relaxation of the southeast trade winds and zonally oriented anomalous warming along the climatological mean axis of the cold tongue.…”

Section: Introductionmentioning

confidence: 99%

“…On the other hand, the Atlantic Niño is widely believed to be dynamically driven because of the Bjerknes feedback (Zebiak 1993;Keenlyside and Latif 2007;Lübbecke and McPhaden 2013;Deppenmeier et al 2016), equatorial Kelvin waves (Brandt et al 2011), and meridional temperature advection from the tropical North Atlantic Ocean (Richter et al 2013).…”

Section: Introductionmentioning

confidence: 99%

An Equatorial–Extratropical Dipole Structure of the Atlantic Niño

Nnamchi

Kucharski

et al. 2016

Journal of Climate

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Equatorial Atlantic variability is dominated by the Atlantic Niño peaking during the boreal summer. Studies have shown robust links of the Atlantic Niño to fluctuations of the St. Helena subtropical anticyclone and Benguela Niño events. Furthermore, the occurrence of opposite sea surface temperature (SST) anomalies in the eastern equatorial and southwestern extratropical South Atlantic Ocean (SAO), also peaking in boreal summer, has recently been identified and termed the SAO dipole (SAOD). However, the extent to which and how the Atlantic Niño and SAOD are related remain unclear. Here, an analysis of historical observations reveals the Atlantic Niño as a possible intrinsic equatorial arm of the SAOD. Specifically, the observed sporadic equatorial warming characteristic of the Atlantic Niño (;0.4 K) is consistently linked to southwestern cooling (;20.4 K) of the Atlantic Ocean during the boreal summer. Heat budget calculations show that the SAOD is largely driven by the surface net heat flux anomalies while ocean dynamics may be of secondary importance. Perturbations of the St. Helena anticyclone appear to be the dominant mechanism triggering the surface heat flux anomalies. A weakening of the anticyclone will tend to weaken the prevailing northeasterlies and enhance evaporative cooling over the southwestern Atlantic Ocean. In the equatorial region, the southeast trade winds weaken, thereby suppressing evaporation and leading to net surface warming. Thus, it is hypothesized that the wind-evaporation-SST feedback may be responsible for the growth of the SAOD events linking southern extratropics and equatorial Atlantic variability via surface net heat flux anomalies.

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“…The tropical Atlantic ocean plays a key role for climate variability in sensitive regions of the surrounding continents: Previous studies suggest that inter-annual variability of sea surface temperature (SST) in the equatorial Atlantic impacts rainfall variability over northeast Brazil and the coastal regions surrounding the Gulf of Guinea Kushnir et al 2006;Brandt et al 2011b). In particular, inter-annual SST variability within the Atlantic cold tongue (ACT) is known to influence the onset and strength of the West African Monsoon (Marin et al 2009;Brandt et al 2011a;Caniaux et al 2011).…”

Section: Introductionmentioning

confidence: 99%