Multidecadal Intensification of Atlantic Tropical Instability Waves

Tuchen, Franz Philip; Perez, Renellys C.; Foltz, Gregory R.; Brandt, Peter; Lumpkin, Rick

doi:10.1029/2022gl101073

Cited by 13 publications

(22 citation statements)

References 71 publications

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“…Recent findings suggest that TIW activity was strongly reduced during the boreal summer of 2021 compared with the summertime TIWs of the last three to four decades (Tuchen, Perez, et al., 2022). One goal of this study is to quantify how the 2021 Atlantic Niño impacted TIW activity and to investigate potential mechanisms.…”

Section: Resultsmentioning

confidence: 99%

“…Variables to which this filter is applied are indicated by a prime (e.g., u ′). In a first step, we focus on the anomalous 2021 TIW season as observed in SST, SSS, Chl‐ a (all at 1°N where these parameters usually show highest TIW‐induced variability, e.g., Tuchen, Perez, et al., 2022; Figures 6a–6c), and SLA at 4°N (Figure 6d). The Hovmoeller diagrams of anomalous TIW‐induced variability show a clear reduction for all parameters during May‐July when compared to climatological values.…”

Section: Resultsmentioning

confidence: 99%

“…Interestingly, TIW‐induced variability is not uniformly reduced throughout the entire summer of 2021, but rebounds in August when higher than normal variability is observed for the four parameters. This results in a delayed onset of the 2021 TIW season and suppression of TIW activity during the climatological peak months of these parameters: July for the peak of TIW‐induced variability in SST and Chl‐ a at 1°N, and SLA at 4°N, and June for the peak of TIW‐induced SSS variability at 1°N (e.g., Olivier et al., 2020; Tuchen, Perez, et al., 2022).…”

Section: Resultsmentioning

confidence: 99%

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Modulation of Equatorial Currents and Tropical Instability Waves During the 2021 Atlantic Niño

Tuchen,

Perez,

Foltz

et al. 2023

JGR Oceans

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In the boreal summer of 2021, the equatorial Atlantic experienced the strongest warm event, that is, Atlantic Niño, since the beginning of satellite observations in the 1970s. Such events have far‐reaching impacts on large‐scale wind patterns and rainfall over the surrounding continents. Yet, developing a paradigm of how Atlantic Niño interacts with the upper‐ocean currents and intraseasonal waves remains elusive. Here we show that the equatorial Kelvin wave associated with the onset of the 2021 Atlantic Niño modulated both the background flow and the eddy flux of the equatorial upper‐ocean circulation, causing an extremely weak and delayed tropical instability wave (TIW) season. TIW‐induced variations of sea surface temperature (SST), sea surface salinity, sea surface height, and eddy temperature advection were exceptionally weak during May to July, the climatological peak of TIW activity, but rebounded in August when higher than normal variability was observed. Moored velocity data at 23°W show that during the peak of the 2021 Atlantic Niño from June to August, the Equatorial Undercurrent was deeper and stronger than usual. An anomalously weak eddy momentum flux strongly suppressed barotropic energy conversion north of the equator from May to July, likely contributing to low TIW activity. Reduced baroclinic energy conversion also might have played a role, as the meridional gradient of SST was sharply reduced during the Atlantic Niño. Despite extremely weak TIW velocities, modest intraseasonal variability of chlorophyll‐a (Chl‐a) was observed during the Atlantic Niño, due to pronounced meridional Chl‐a gradients that partly compensated for the weak TIWs.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Modulation of Equatorial Currents and Tropical Instability Waves During the 2021 Atlantic Niño

Tuchen,

Perez,

Foltz

et al. 2023

JGR Oceans

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“…Other mechanisms that are suggested to impact the strength of equatorial cooling on decadal time scales include the decadal variability of TIWs. A decadal strengthening of TIWs was found to be associated with enhanced warming of the equatorial cold tongue by lateral eddy fluxes (Tuchen et al 2022b). Coupled climate simulations also suggest the importance of surface heat fluxes in driving interannual to decadal cold tongue SST variability (Nnamchi et al 2015).…”

Section: Relation Between Upwelling Seasonality and Longer-term Varia...mentioning

confidence: 82%

“…However, other processes such as lateral mixing, responsible for reducing nitrate concentrations in upwelling regions, or surface heat fluxes, might contribute as well. Recently, the multidecadal increase in the strength of TIWs and associated equatorward eddy heat flux was suggested to warm the EAUS (Tuchen et al 2022b). Such eddy fluxes generally oppose the Ekman transport in upwelling systems.…”

Section: Discussionmentioning

confidence: 99%

Physical processes in the upwelling regions of the tropical Atlantic

Brandt

Alory²,

Rouault³

et al. 2022

Preprint

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Abstract. In this paper, we review observational and modelling results on the upwelling in the inner tropical Atlantic. We focus on the physical processes that drive the seasonal variability of surface cooling and upward nutrient flux required to explain the seasonality of primary productivity. We separately consider the equatorial upwelling system, the northern coastal upwelling system of the Gulf of Guinea and the tropical Angolan upwelling system. For the equatorial regime, we discuss the forcing of upwelling velocity and turbulent mixing as well as the underlying dynamics responsible for thermocline movements and current structure. The coastal upwelling system in the Gulf of Guinea is concentrated along northern boundary and is driven by both, local and remote forcing. The particular role of the Guinea Current, nonlinearity and the shape of the coastline are emphasized. For the tropical Angolan upwelling, we show that this system is not wind-driven, but instead results from the combined effect of coastally trapped waves, surface heat and freshwater fluxes, and turbulent mixing. Finally, we review recent changes in the upwelling systems associated with climate variability and global warming and address possible responses of upwelling systems in future scenarios.

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Origins of Biweekly Sea Surface Temperature Variability in the Eastern Equatorial Pacific and Atlantic

Xu,

Chang,

Zhang

2024

Geophysical Research Letters

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Biweekly sea surface temperature (SST) variability significantly contributes to over 50% of the intraseasonal variability in the eastern equatorial Pacific (EEP) and Atlantic (EEA). Our study investigates this biweekly variability, employing a blend of in–situ and reanalysis data sets. The research identifies biweekly signals in SST, meridional wind, and ocean currents, notably in September–November in EEP and June–August in EEA. Biweekly southerly (northerly) winds drive instantaneous northward (southward) ocean currents in EEP, but with a 1–2‐day phase delay in EEA. Consequently, these currents lead to SST anomalies with a 3–4‐day lag in both EEP and EEA due to the presence of the cold tongue. The study reveals the origin of biweekly wind fluctuations in the western Pacific for EEP and the subpolar Pacific for EEA, connected by atmospheric Rossby waves validated through a linearized non‐divergent barotropic model. This research affirms the influence of subtropical and subpolar atmospheric forcing on equatorial SST.

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Multidecadal Intensification of Atlantic Tropical Instability Waves

Abstract: The upper-ocean circulation in the tropical Atlantic is characterized by energetic zonal currents that facilitate a large cross-basin volume exchange and transformation of water masses (e.g.,

Cited by 13 publications

References 71 publications

Modulation of Equatorial Currents and Tropical Instability Waves During the 2021 Atlantic Niño

Modulation of Equatorial Currents and Tropical Instability Waves During the 2021 Atlantic Niño

Physical processes in the upwelling regions of the tropical Atlantic

Origins of Biweekly Sea Surface Temperature Variability in the Eastern Equatorial Pacific and Atlantic

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