Transports, frontal motions and eddies at the Brazil-Malvinas currents confluence

Garzoli, Silvia L.; Garraffo, Zulema

doi:10.1016/0198-0149(89)90145-3

Cited by 118 publications

(89 citation statements)

References 11 publications

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“…Three different parameters obtained from the altimeter-derived upper layer thickness maps, which characterize the geometry of the BC front, are analyzed here: (1) the frontal time density, (2) (Figures 6b and 6d) show that the longitude has peaks at 2.5, 3, and 6 months and the latitude also has multiple peaks, at 2, 3, 6, and 12 months, all significant at the 85% level. These results agree with previous estimates from a 1 year long record of inverted echosounder data [Garzoli and Garraffo, 1989] Figure 7a) and a standard deviation of 7 Sv. The power spectrum corresponding to this time series shows multiple peaks, at 3, 6, and 12 months, which are significant at the 85% level (Figure 7b).…”

Section: Resultssupporting

confidence: 83%

“…Therefore the BC frontal location can be investigated in terms of the position of the main thermocline, which is closely related to the upper ocean dynamics. The variability of the depth of two isotherms, 8 ø and 10øC, which are associated with the main thermocline, has been linked to the dynamic height anomaly referenced to 1500 m [Gordon, 1989;Garzoli and Garraffo, 1989]. The location at which these two isotherms are found at -200 m depth has also been linked to the location of the surface and subsurface fronts [Garzoli and Garraffo, 1989].…”

Section: Introductionmentioning

confidence: 99%

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Investigation of the Brazil Current front variability from altimeter data

Goñi¹,

Wainer²

2001

J. Geophys. Res.

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Abstract. The southwestern Atlantic Ocean is characterized by the confluence of the Brazil and Malvinas Currents, which form very strong surface and subsurface fronts that can be detected from hydrographic and remote sensing observations. Three data sets, consisting of TOPEX/Poseidon-derived sea height anomalies, the climatologically derived depth of the 10øC isotherm, and reduced gravity, are used in conjunction with a two-layer dynamical ocean scheme to monitor the Brazil Current front and to investigate its variability during a 6 year period (1993)(1994)(1995)(1996)(1997)(1998). Results reveal that the fronts exhibit motions that are larger zonally than meridionally, showing strong interannual variability with annual mean amplitudes that range from 1 ø to 6 ø. The annual and semiannual components account for more than 75% of the variability of the frontal oscillations. In the annual cycle the frontal motions appear to be related closely to fluctuations in the baroclinic transport of the Brazil Current and are only influenced by the Malvinas Current when the Brazil Current transport is very small.

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Section: Resultssupporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Investigation of the Brazil Current front variability from altimeter data

Goñi¹,

Wainer²

2001

J. Geophys. Res.

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“…Offshore in the upper water column, the mean flow reversal and high variability suggests the presence of strong anti-cyclonic circulations most likely associated with the retroflection of the Brazil Current just to the south at the Brazil-Malvinas Confluence (e.g. Olson et al, 1988;Garzoli and Garraffo, 1989). This retroflection appears to be much tighter than was suggested in some earlier studies (Peterson and Stramma, 1991;Stramma and England, 1999), but it resembles the circulation pattern of satellite-derived mean dynamic topography (Rio and Hernandez, 2004) and the OFES numerical simulation (Fig.…”

Section: Absolute Velocity and Transportmentioning

confidence: 47%

“…The strong, highly varying flow in the upper water column on the western side of the array is associated with the Brazil Current, which is thought to be confined above ∼ 800 dbar (e.g. Garzoli and Garraffo, 1989), while the upper water column flow on the east side is likely associated with the meandering of retroflected waters coming from the Brazil-Malvinas Confluence to the south (e.g. see velocity vectors in Fig.…”

Section: Absolute Velocity and Transportmentioning

confidence: 99%

Deep Western Boundary Current transport variability in the South Atlantic: preliminary results from a pilot array at 34.5° S

et al. 2012

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Abstract. The first direct estimates of the temporal variability of the absolute transport in the Deep Western Boundary Current (DWBC) at 34.5 • S in the South Atlantic Ocean are obtained using just under one year of data from a line of four pressure-equipped inverted echo sounders. Hydrographic sections collected in 2009 and 2010 confirm, based on neutral density, temperature, salinity, and oxygen values, the presence of the DWBC, one of the main deep pathways of the Meridional Overturning Circulation. Both data sets indicate that the DWBC reconstitutes itself after breaking into eddies in the western sub-tropical Atlantic near 8 • S. The amplitude and spectral character of the DWBC transport variability are comparable with those observed in the North Atlantic, where longer records exist, with the DWBC at 34.5 • S exhibiting a transport standard deviation of 25 Sv and variations of ∼ 40 Sv occurring within periods as short as a few days. There is little indication of an annual cycle in the DWBC transports, although the observational records are too short to be definitive. A Monte Carlo-style analysis using 27 yr of model output from the same location as the observations indicates that about 48-60 months of data will be required to fully assess the deep transport variability. The model suggests the presence of an annual cycle in DWBC transport, however its statistical significance with even 27 yr of model output is low, suggesting that seasonal variations in the model are weak.

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“…The Gulf Stream is highly influenced by mesoscale circulation and the growth of baroclinic instability after its separation from the North American coast (Robinson et al, 1989;Spall and Robinson, 1990;Lee and Mellor, 2003). Also, the Brazil-Malvinas Confluence is characterized by a weak and warm southward Brazil Current meeting a strong, cold and less saline northward Malvinas Current, which results in large contrasts in stratification and strong eddy activity (Gordon, 1989;Garzoli and Garrafo, 1989;Goni et al, 1996). Thus, the large RMSD still found in the assimilation runs in these regions can be due to lack of data, inaccuracies in the ensemble members, and limitation of the model resolution to solve the mesoscale circulation patterns.…”

Section: Comparison With Argo Profilers and Pirata Mooringsmentioning

confidence: 99%

Argo data assimilation into HYCOM with an EnOI method in the Atlantic Ocean

et al. 2015

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Abstract. An ocean data assimilation system to assimilate Argo temperature (T ) and salinity (S) profiles into the HYbrid Coordinate Ocean Model (HYCOM) was constructed, implemented and evaluated for the first time in the Atlantic Ocean (78 • S to 50 • N and 98 • W to 20 • E). The system is based on the ensemble optimal interpolation (EnOI) algorithm proposed by Xie and Zhu (2010), especially made to deal with the hybrid nature of the HYCOM vertical coordinate system with multiple steps. The Argo T -S profiles were projected to the model vertical space to create pseudoobserved layer thicknesses ( p obs ), which correspond to the model target densities. The first step was to assimilate p obs considering the sub-state vector composed by the model layer thickness ( p) and the baroclinic velocity components. After that, T and S were assimilated separately. Finally, T was diagnosed below the mixed layer to preserve the density of the model isopycnal layers. Five experiments were performed from 1 January 2010 to 31 December 2012: a control run without assimilation, and four assimilation runs considering the different vertical localizations of T , S and p. The assimilation experiments were able to significantly improve the thermohaline structure produced by the control run. They reduced the root mean square deviation (RMSD) of T and S calculated with respect to Argo independent data in 34 and 44 %, respectively, in comparison to the control run. In some regions, such as the western North Atlantic, substantial corrections in the 20 • C isotherm depth and the upper ocean heat content towards climatological states were achieved.The runs with a vertical localization of p showed positive impacts in the correction of the thermohaline structure and reduced the RMSD of T (S) from 0.993 • C (0.149 psu) to 0.905 • C (0.138 psu) for the whole domain with respect to the other assimilation runs.

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Transports, frontal motions and eddies at the Brazil-Malvinas currents confluence

Cited by 118 publications

References 11 publications

Investigation of the Brazil Current front variability from altimeter data

Investigation of the Brazil Current front variability from altimeter data

Deep Western Boundary Current transport variability in the South Atlantic: preliminary results from a pilot array at 34.5° S

Argo data assimilation into HYCOM with an EnOI method in the Atlantic Ocean

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