Submesoscale Phenomena Due to the Brazil Current Crossing of the Vitória‐Trindade Ridge

Napolitano, Dante Campagnoli; Silveira, Ilson Carlos Almeida da; Tandon, Amit; Calil, Paulo H. R.

doi:10.1029/2020jc016731

Cited by 13 publications

(15 citation statements)

References 80 publications

(200 reference statements)

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“…(2016) from the analysis of 13 years of ADCP data in the Drake Passage. The departure from the QG regime observed during winter and early spring is consistent with reports of increased submesoscale activity in numerical simulations at this period (e.g., Callies et al., 2015; Napolitano et al., 2021; Rocha, Chereskin, et al., 2016; Sasaki et al., 2014), being also detected in altimetry data (Dufau et al., 2016; Vergara et al., 2019) and by in situ observations (Callies et al., 2015). In winter, when the mixed layer is deep and stratification is weak, there is more available potential energy and the EKE produced by mixed‐layer instabilities is higher than in summer, when the opposite occurs (Callies et al., 2015).…”

Section: The Surface Kinetic Energy Spectra In the South Atlanticsupporting

confidence: 90%

“…In winter, when the mixed layer is deep and stratification is weak, there is more available potential energy and the EKE produced by mixed‐layer instabilities is higher than in summer, when the opposite occurs (Callies et al., 2015). The seasonal cycle of the mixed layer thus affect the KE and consequently the spectral slopes, and it may be altered (not exclusively) by the presence of submesoscale instabilities (e.g., Sasaki et al., 2014), inertia‐gravity waves (e.g., Rocha, Chereskin, et al., 2016), and flow‐topography interactions (e.g., Napolitano et al., 2021). For more details in the seasonality of KE spectra, see Uchida et al.…”

Section: The Surface Kinetic Energy Spectra In the South Atlanticmentioning

confidence: 99%

“…Sasaki et al (2014) showed that there is an important seasonal cycle driven by the atmosphere which affects the SSH variability in a high-eddy-energy region on the North Atlantic. During summer, a shallow MLD imply low available potential energy, whereas in winter a deeper MLD have the opposite effect (Callies et al, 2015;Napolitano et al, 2021). In addition, the mixed layer is not horizontally homogeneous, and horizontal density gradients can modify its thickness and horizontal structures (Tandon & Garrett, 1995).…”

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confidence: 99%

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Can the Surface Quasi‐Geostrophic (SQG) Theory Explain Upper Ocean Dynamics in the South Atlantic?

et al. 2022

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Satellite altimeters provide quasi‐global measurements of sea surface height, and from those the vertically integrated geostrophic velocity can be directly estimated, but not its vertical structure. This study discusses whether the mesoscale (30–400 km) dynamics of three regions in the South Atlantic can be described by the surface quasi‐geostrophic (SQG) theory, both at the surface and in depth, using outputs from an ocean general circulation model. At these scales, the model surface eddy kinetic energy (EKE) spectra show slopes close to k−5/3 (k−3) in winter (summer), characterizing the SQG and quasi‐geostrophic (QG) turbulence regimes. We use surface density and temperature to (a) reconstruct the stream function under the SQG theory, (b) assess its capability of reproducing mesoscale motions, and (c) identify the main parameters that improve such reconstruction. For mixed layers shallower than 100 m, the changes in the mixed‐layer depth contributes nine times more to the surface SQG reconstruction than the EKE, indicating the strong connection between the quality of the reconstruction and the seasonality of the mixed layer. To further explore the reconstruction vertical extension, we add the barotropic and first baroclinic QG modes to the surface solution. The SQG solutions reproduce the model density and geostrophic velocities in winter, whereas in summer, the interior QG modes prevail. Together, these solutions can improve surface correlations (>0.98) and can depict spatial patterns of mesoscale structures in both the horizontal and vertical domains. Improved spatial resolution from upcoming altimeter missions poses a motivating scenario to extend our findings into future observational studies.

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Section: The Surface Kinetic Energy Spectra In the South Atlanticsupporting

confidence: 90%

Section: The Surface Kinetic Energy Spectra In the South Atlanticmentioning

confidence: 99%

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confidence: 99%

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Can the Surface Quasi‐Geostrophic (SQG) Theory Explain Upper Ocean Dynamics in the South Atlantic?

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“…Low PV values are prone to instabilities (D'Asaro et al, 2011;Thomas et al, 2008Thomas et al, , 2013. Here, we evaluate the two-dimensional PV (e.g., Lazaneo et al, 2020;Napolitano et al, 2021;Ramachandran et al, 2018;Thomas et al, 2016) from the objectively mapped field. If one assumes that the features are indeed SCVs and that the sampling of the SCV currents and density occurs through their centers, then an approximation of the Ertel PV is possible.…”

Section: The Scv Vertical Structurementioning

confidence: 99%

Submesoscale Coherent Vortices in the South Atlantic Ocean: A Pathway for Energy Dissipation

et al. 2022

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Mesoscale eddies propagate westward across the South Atlantic basin. As they reach the westernmost part of the basin, at approximately 20°S, they interact with a quasi‐zonal seamount chain, the Vitória‐Trindade Ridge (VTR). The interactions with the local topography lead to submesoscales instabilities, which ignite the formation of submesoscale coherent vortices (SCVs) such as those described in the present study for the first time in the VTR region. Here, using high‐resolution hydrographic and microstructure measurements, we describe the dynamics of two adjacent SCVs wandering through the ridge. We find that the anticyclonic SCVs are characterized by a low potential vorticity and angular momentum signature, and are therefore prone to both centrifugal and symmetric instabilities. This dynamic regime suggests small‐scale turbulence is actively cascading energy down to dissipation, diagnosed from turbulent kinetic energy dissipation estimates within one of the SCVs through microstructure measurements. The energy dissipation levels observed within the SCV are two orders of magnitude larger than in surrounding waters. The thermohaline signatures of each SCV reveal homogenized waters in their cores but with small thermohaline anomalies when compared to surrounding waters, suggesting a remote generation site. Here, we argue that such vortices are essential agents for energy dissipation in the ocean. We speculate that the observed SCVs were formed due to mesoscale eddy‐topography interaction along the VTR and advected by the meandering South Equatorial Current to the location of field observations.

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“…Transformation of PV is key in setting the dynamics of the EUC in the Gulf of Guinea. Due to the presence of the islands and topography, both friction and diapycnal mixing must play a prominent role, since flow-topography interactions are known to induce strong mixing (e.g., Lueck & Mudge, 1997;Naveira Garabato et al, 2004) and introduce PV anomalies (e.g., Gula et al, 2019;Napolitano et al, 2020;Wenegrat et al, 2018). Assene et al (2020) showed that isopycnal mixing also takes place during the rearranging of PV anomalies into eddies.…”

Section: Pv Anomalies In the Eucmentioning

confidence: 99%

Influence of the Gulf of Guinea Islands on the Atlantic Equatorial Undercurrent Circulation

et al. 2022

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Velocity observations show that the EUC hits São Tomé Island at 6 • E, forcing the jet to bifurcate earlier than if the island did not exist;• The EUC dynamics and the location of São Tomé impose an asymmetry to the 10 bifurcation, affecting net zonal fluxes in the tropical Atlantic; 11 • The EUC-island encounter triggers vertical advection and transformation of the 12 EUC water via diapycnal and isopycnal mixing and friction.

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Submesoscale Phenomena Due to the Brazil Current Crossing of the Vitória‐Trindade Ridge

Cited by 13 publications

References 80 publications

Can the Surface Quasi‐Geostrophic (SQG) Theory Explain Upper Ocean Dynamics in the South Atlantic?

Can the Surface Quasi‐Geostrophic (SQG) Theory Explain Upper Ocean Dynamics in the South Atlantic?

Submesoscale Coherent Vortices in the South Atlantic Ocean: A Pathway for Energy Dissipation

Influence of the Gulf of Guinea Islands on the Atlantic Equatorial Undercurrent Circulation

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