Is There Evidence of Changes in Tropical Atlantic Variability Modes under AMO Phases in the Observational Record?

Martín‐Rey, Marta; Polo, Irene; Rodríguez‐Fonseca, Belén; Losada, Teresa; Lazar, Alban

doi:10.1175/jcli-d-16-0459.1

Cited by 82 publications

(103 citation statements)

References 96 publications

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“…INTER simulation reproduces the observational results of Martín‐Rey et al (), hereinafter MR18, for the 1968‐1995 period (Figure a‐b). The Atlantic Niño and HS emerge as the first two leading modes, exhibiting significant equatorial SST anomalies.…”

Section: Resultssupporting

confidence: 83%

“…The basin‐wide Atlantic Niño pattern described in MR18 for negative AMV phases is well reproduced by INTER (Figure a and Figure S1a). INTER also simulates the general reduction of tropical trades during previous winter‐spring (Figure b,f), caused by a simultaneous weakening of the Subtropical Highs (Martín‐Rey et al, ). Interestingly, The Atlantic Niño during negative AMV exhibits an early development, starting from previous fall‐winter (Figure d) and it is characterized by a westward extension of its equatorial warm tongue (Figure a), compared with the canonical Atlantic Niño (see Figure in Martín‐Rey et al, ; Losada & Rodríguez‐Fonseca, ).…”

Section: Resultsmentioning

confidence: 99%

“…The amplitude of interannual SST anomalies, and thus the interannual modes, are strongly influenced by low‐frequency variability associated with natural decadal patterns (i.e: Atlantic Multidecadal Variability; Pacific Decadal variability) or the anthropogenic forcing (Martín‐Rey et al, ; Tokinaga & Xie, ). These low‐frequency signals can modulate the amplitude and structure of the SST anomalies in the tropical Atlantic, giving rise to the decadal modulation of the interannual modes (Losada & Rodríguez‐Fonseca, ; Martín‐Rey et al, ). However, in the present study we focus on the interannual variability modes that emerge during a negative AMV period.…”

Section: Methodsmentioning

confidence: 99%

“…The co‐existence of Atlantic Niño and HS during negative AMV phases, is understood in terms of a distinct contribution of the Subtropical Highs acting under shallow mean thermocline conditions in the eastern equatorial Atlantic. This could imply a more effective Bjerknes feedback (Bjerknes, ), enhancing the equatorial SST variability and making the TA more receptive to external forcings (Martín‐Rey et al, ). The emergence of different configurations of the Equatorial Mode is a key element to understand the multidecadal changes experienced by TAV, since different Atlantic Niño structures have been associated with a modification of its climate impacts (Losada & Rodríguez‐Fonseca, ; Losada, Rodríguez‐Fonseca, & Kucharski, ; Martín‐Rey et al, ; Martín‐Rey 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: 83%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

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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“…It follows that the apparent discrepancies between our work and Lübbecke and McPhaden's () study must be partially attributed to the different analysis periods. In agreement with Martín‐Rey et al's () proposed nonstationarity of the Atlantic Niño itself, the Atlantic Bjerknes feedback appears to vary on decadal time scales.…”

Section: Stationarity Of the Bjerknes Feedbacksupporting

confidence: 88%

A Comparison of the Atlantic and Pacific Bjerknes Feedbacks: Seasonality, Symmetry, and Stationarity

2019

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The Bjerknes feedback is the dominant positive feedback in the equatorial ocean basins. To examine the seasonality, symmetry, and stationarity of the Pacific and Atlantic Bjerknes feedbacks we decompose them into three feedback elements that relate thermocline depth, sea surface temperature, and western basin wind stress variability to each other. We partition feedback elements into composites associated with positive or negative anomalies. Using robust regression, we diagnose the strength of each composite. For the recent period 1993–2012, composites of the Pacific Bjerknes feedback elements agree well with previous work. Positive composites are generally stronger than negative composites, and all feedback elements are weakest in late boreal spring. In the Atlantic, differences between positive and negative composites are less consistent across feedback elements. Specifically, wind variability seems to play a less important role in shaping atmosphere‐ocean coupling in the Atlantic when compared to the Pacific. However, a clear seasonality emerges: Feedback elements are generally strong in boreal summer and, for the negative composites, again in boreal winter. The Atlantic Bjerknes feedback is dominated by subsurface‐surface coupling. Applying our analysis to overlapping 25‐year periods for 1958–2009 shows that the strengths of feedback elements in both ocean basins vary on decadal time scales. While the overall asymmetry of the Pacific Bjerknes feedback is robust, the strength and symmetry of Atlantic feedback elements vary considerably between decades. Our results indicate that the Atlantic Bjerknes feedback is nonstationary on decadal time scales.

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