Equatorial Atlantic interannual variability and its relation to dynamic and thermodynamic processes

Jouanno, Julien; Hernández, O; Sánchez-Gómez, Emilia; Deremble, Bruno

doi:10.5194/esd-2017-58

Cited by 11 publications

(16 citation statements)

References 3 publications

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“…Our results from the heat budget analysis, confirm that air‐sea fluxes are the main drivers of the HS branches and southwestern lobe of the Atlantic Niño mode. Furthermore, we provide further evidence of the fundamental role of ocean dynamics to generate and modulate the equatorial SST variability (Dippe et al, ; Foltz et al, ; Jouanno et al, ; Polo et al, ). It is noteworthy that both thermocline and advective feedback have a substantial contribution in the development of the Atlantic Niño warm tongue, while thermocline feedback appears as dominant in the generation of the HS pattern.…”

Section: Resultssupporting

confidence: 61%

“…This disagrees with the results from Nnamchi et al (); (), which claimed for the thermodynamic origin of the Atlantic Niño. However, Nnamchi et al () findings are based on coupled climate models that present a strong bias in their oceanic component (Wang et al, ), causing an overestimation of the thermodynamic contribution (Jouanno et al, ). On its part, Nnamchi et al () study of reanalysis datasets is based in an approximated estimation of a not‐closed heat budget analysis, in which the air‐sea fluxes present a significant but not unique contribution to the mixed layer temperature trend (Nnamchi et al, ).…”

Section: Resultsmentioning

confidence: 99%

“…Recent studies have questioned the air‐sea interactions and ocean mechanisms responsible to develop the Atlantic Niño, becoming a controversial topic (Brandt et al, ; Jouanno et al, ; Lübbecke et al, ; Nnamchi et al, , ; Planton et al, ; Richter et al, ). Traditionally, it has been established that a relaxation of south‐easterly trades related to an anomalous weakening of the South Atlantic Anticyclone (SAA), leads the generation of the Atlantic Niño (Lübbecke et al, ; Polo, Rodríguez‐Fonseca, et al, ).…”

Section: Introductionmentioning

confidence: 99%

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Ocean Dynamics Shapes the Structure and Timing of Atlantic Equatorial Modes

et al. 2019

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A recent study has brought to light the co-existence of two distinct Atlantic Equatorial Modes during negative phases of the Atlantic Multidecadal Variability: the Atlantic Niño and Horse-Shoe (HS) mode. Nevertheless, the associated air-sea interactions for HS mode have not been explored so far and the prevailing dynamic view of the Atlantic Niño has been questioned. Here, using a forced ocean model simulation, we find that for both modes, ocean dynamics is essential to explain the equatorial SST variations, while air-sea fluxes control the off-equatorial SST anomalies. Moreover, we demonstrate the key role played by ocean waves in shaping their distinct structure and timing. For the positive phase of both Atlantic Niño and HS, anomalous westerly winds trigger a set of equatorial downwelling Kelvin waves (KW) during spring-summer. These dKWs deepen the thermocline, favouring the equatorial warming through vertical diffusion and horizontal advection. Remarkably, for the HS, an anomalous north-equatorial wind stress curl excites an upwelling Rossby wave (RW), which propagates westward and is reflected at the western boundary becoming an equatorial upwelling KW. The uKW propagates to the east, activating the thermocline feedbacks responsible to cool the sea surface during summer months. This RW-reflected mechanism acts as a negative feedback causing the early termination of the HS mode. Our results provide an improvement in the understanding of the TAV modes and emphasize the importance of ocean wave activity to modulate the equatorial SST variability. These findings could be very useful to improve the prediction of the Equatorial Modes.Plain Language Summary A recent study has found how the inter-annual variations of sea surface temperature (SST) in the tropical Atlantic, are organized in two different equatorial modes during negative phases of the Atlantic Multidecadal Variability. These modes, which illustrate a particular and distinct spatial structure, are denoted as Atlantic Niño and Horse-Shoe mode. Here we show that, for both patterns, ocean dynamics is key to generate equatorial SSTs, while the off-equatorial SST anomalies are mainly explained by thermodynamic processes (heat fluxes exchanges). Outstandingly, we demonstrate that ocean waves have a substantial impact in the development and decay of Atlantic Niño and Horse-Shoe modes, shaping their distinct spatial configuration and timing. Our results bring to light the importance of ocean wave activity to explain the modulation of the equatorial Atlantic SST variability, which could be relevant to improve its predictability and associated climatic impacts.

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Section: Resultssupporting

confidence: 61%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ocean Dynamics Shapes the Structure and Timing of Atlantic Equatorial Modes

et al. 2019

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“…The main consequence of the equatorially enhanced turbulence below the mixing layer, both in the tropical Atlantic and Pacific, is the strongly enhanced diapycnal fluxes of heat, freshwater, and nutrients that contribute to controlling the mean state and variability of SST, SSS, and primary production (e.g., Gregg et al, ; Hummels et al, ; Moum et al, ; Sandel et al, ; Schlundt et al, ; Wang & McPhaden, ). Furthermore, the results from the measurement program verified results from model studies that had shown elevated mixing to occur within the ACT region along with consequences for the heat and freshwater budget of the ACT and the Gulf of Guinea region (Camara et al, ; Da‐Allada et al, , , ; Jouanno et al, , ; Planton et al, ).…”

Section: Additional Results In Cooperation With Other National and Insupporting

confidence: 62%

PIRATA: A Sustained Observing System for Tropical Atlantic Climate Research and Forecasting

Bourlès

Araújo

McPhaden

et al. 2019

Earth and Space Science

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Prediction and Research Moored Array in the Tropical Atlantic (PIRATA) is a multinational program initiated in 1997 in the tropical Atlantic to improve our understanding and ability to predict ocean‐atmosphere variability. PIRATA consists of a network of moored buoys providing meteorological and oceanographic data transmitted in real time to address fundamental scientific questions as well as societal needs. The network is maintained through dedicated yearly cruises, which allow for extensive complementary shipboard measurements and provide platforms for deployment of other components of the Tropical Atlantic Observing System. This paper describes network enhancements, scientific accomplishments and successes obtained from the last 10 years of observations, and additional results enabled by cooperation with other national and international programs. Capacity building activities and the role of PIRATA in a future Tropical Atlantic Observing System that is presently being optimized are also described.

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“…Warm DT10A extend further south continuously up to around 25°S, corresponding to the approximate maximum latitude where the signature of Benguela Niños and corresponding interannual CTWs can be tracked (Bachèlery et al, ). The warm T10 anomaly with values greater than 0.5 °C extends northwestward into the eastern equatorial Atlantic region up to 15°W, a region with a strong seasonal cycle of SST (the seasonal formation of the Atlantic Cold Tongue) which is modulated interannually by the so‐called Atlantic Equatorial Mode often referred to Atlantic Niño with peak variability in Austral winter (Jouanno et al, , ; Lübbecke et al, ). The wind stress anomalies during the mature phase of the selected extreme events reveal persisting northerly anomalies over the warm areas along the Angolan coast.…”

Section: Resultsmentioning

confidence: 99%

Benguela Niños and Benguela Niñas in Forced Ocean Simulation From 1958 to 2015

et al. 2019

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A systematic study of Benguela Niño and Benguela Niña events during 1958 to 2015 including those that developed before the satellite era (1982) is carried out using an ocean general circulation model in combination with a linear equatorial model. Altogether, 21 strong warm and cold anomalous coastal events are identified among which 6 undocumented extreme coastal events are reported. Results suggest that most of these extreme coastal events including the newly identified ones are linked to remote equatorial forcing via mode 2 equatorial Kelvin waves. The latter propagates after approaching the African coast poleward as coastally trapped waves leading surface temperature anomalies along the Angola‐Benguela current system by one month. One to two months before the peak of Benguela Niños or Niñas usually occurring in March–April, a large‐scale wind stress forcing is observed with both local (variations of alongshore coastal wind stress) and remote forcing developing simultaneously. Results further suggest that surface temperature anomalies off Southern Angola and in the Angola‐Benguela Front are associated with equatorial dynamics and meridional wind stress fluctuations off the southwestern African coast north of 15°S. Similar mechanisms are observed for Northern Namibia in combination with forcing by local meridional wind stress variations.

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Equatorial Atlantic interannual variability and its relation to dynamic and thermodynamic processes

Cited by 11 publications

References 3 publications

Ocean Dynamics Shapes the Structure and Timing of Atlantic Equatorial Modes

Ocean Dynamics Shapes the Structure and Timing of Atlantic Equatorial Modes

PIRATA: A Sustained Observing System for Tropical Atlantic Climate Research and Forecasting

Benguela Niños and Benguela Niñas in Forced Ocean Simulation From 1958 to 2015

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