Brazil Current surface circulation and energetics observed from drifting buoys

[1] The southwestern Atlantic mean surface circulation, its associated variability and energetics are studied through the analysis of 13 years of surface drifter data binned onto a 0.5° × 0.5° grid. Special attention is given to the following three main regional features of the domain: the Brazil Current, the Malvinas Current, and the Brazil-Malvinas Confluence. For the western boundary currents, the mean field reveals velocities larger than 45 cm s−1, associated with high levels of variability (standard deviation of more than 15 cm s−1), while the highest values of standard deviation are found in the Brazil-Malvinas Confluence (>25 cm s−1). Conversely, over most of the domain the mean velocities found (20–30 cm s−1) and associated standard deviations (<15 cm s−1) are generally lower. High values of kinetic energy of the mean flow per unit mass (265–1000 cm2 s−2) are estimated in the western boundary currents and their extensions. Eddy kinetic energy along the main jet of the western boundary currents is generally lower than the kinetic energy of the mean flow, except for some areas along the Brazil Current path. In contrast, the Brazil-Malvinas Confluence reveals eddy kinetic energy levels comparable or larger (∼2500 cm2 s−2) than the mean kinetic energy. Away from the boundary, most of the kinetic energy of the surface circulation is in the eddy field. Furthermore, the analysis of the kinetic energy conversion term suggests the presence of barotropic instabilities along the Brazil Current. Over most of the Brazil Current core, the kinetic energy conversion term points from the mean to eddy kinetic energy.

[1]  C. Provost,et al.  Direct velocity measurements in the Malvinas Current , 1999 .

[2]  P. Poulain,et al.  Quality Control and Interpolations of WOCE-TOGA Drifter Data , 1996 .

[3]  Y. Ishikawa,et al.  Global Surface Circulation and Its Kinetic Energy Distribution Derived from Drifting Buoys , 1997 .

[4]  L. A. Anderson,et al.  Estimates of the energy cycle of the oceans , 1994 .

[5]  W. Emery,et al.  Variability and forcing of the East Australian Current , 2005 .

[6]  R. Morrow,et al.  Eddy kinetic energy and momentum flux in the Southern Ocean: Comparison of a global eddy‐resolving model with altimeter, drifter, and current‐meter data , 1994 .

[7]  L. Stramma,et al.  The South Atlantic Current , 1990 .

[8]  S. Gille.  The Southern Ocean Momentum Balance: Evidence for Topographic Effects from Numerical Model Output and Altimeter Data , 1997 .

[9]  A. Assireu,et al.  Surface circulation and kinetic energy in the SW Atlantic obtained by drifters , 2003 .

[10]  P. M. Saunders,et al.  Bottom Currents Derived from a Shipborne ADCP on WOCE Cruise A11 in the South Atlantic , 1995 .

[11]  W. Dewar,et al.  Gulf Stream Dynamics. Pad II: Eddy Energetics at 73°W , 1989 .

[12]  I. D. da Silveira,et al.  A parametric model for the Brazil Current meanders and eddies off southeastern Brazil , 2006 .

[13]  B. Cushman-Roisin.  Introduction to Geophysical Fluid Dynamics , 1994 .

[14]  W. White,et al.  Horizontal Eddy Fluxes of Momentum and Kinetic Energy in the Near-Surface of the Kuroshio Extension , 1982 .

[15]  M. Cronin,et al.  Eddy–Mean Flow Interaction in the Gulf Stream at 68°W. Part I: Eddy Energetics , 1996 .

[16]  Martin Saraceno,et al.  On the relationship between satellite‐retrieved surface temperature fronts and chlorophyll a in the western South Atlantic , 2005 .

[17]  K. Wyrtki,et al.  Eddy energy in the oceans , 1976 .

[18]  P. Leeuwen,et al.  Generation and Evolution of Natal Pulses: Solitary Meanders in the Agulhas Current , 1999 .

[19]  A. Gordon,et al.  Satellite observations of the Brazil and Falkland currents— 1975 1976 and 1978 , 1982 .

[20]  S. Levitus,et al.  New estimates of the available potential energy in the world ocean , 1989 .

[21]  Brian D. Beckley,et al.  Global mesoscale variability from collinear tracks of SEASAT altimeter data , 1983 .

[22]  J. Pedlosky.  The Stability of Currents in the Atmosphere and the Ocean: Part I , 1964 .

[23]  E. Hofmann.  Erratum: Correction to ``The large-scale horizontal structure of the Antarctic Circumpolar Current from FGGE drifters'' , 1985 .

[24]  J. Church,et al.  Eddy shedding and energy conversions in the East Australian Current , 2006 .

[25]  J. S. Godfrey,et al.  Regional Oceanography: An Introduction , 1994 .

[26]  Donald B. Olson,et al.  RINGS IN THE OCEAN , 1991 .

[27]  E. Campos,et al.  Shelf break upwelling driven by Brazil Current Cyclonic Meanders , 2000 .

[28]  P. Leeuwen,et al.  Natal pulses and the formation of Agulhas rings , 2000 .

[29]  David M. Fratantoni,et al.  North Atlantic surface circulation during the 1990's observed with satellite-tracked drifters , 2001 .

[30]  J. Servain,et al.  Tropical instability waves at 0°N, 23°W in the Atlantic: A case study using Pilot Research Moored Array in the Tropical Atlantic (PIRATA) mooring data , 2005 .

[31]  Geoffrey Ingram Taylor,et al.  Diffusion by Continuous Movements , 1922 .

[32]  Eddy statistics in the South Atlantic as derived from drifters drogued at 100 m , 1995 .

[33]  David Griffin,et al.  Divergent pathways of cyclonic and anti‐cyclonic ocean eddies , 2004 .

[34]  M. M. Mata,et al.  Os processos de conversão de energia nos oceanos: uma revisão do Diagrama de Lorenz , 2008 .

[35]  S. L. Patterson.  Surface Circulation and Kinetic Energy Distributions in the Southern Hemisphere Oceans from FGGE Drifting Buoys , 1985 .

[36]  Philip L. Richardson,et al.  Eddy kinetic energy in the North Atlantic from surface drifters , 1983 .

[37]  D. Chelton,et al.  Seasonal variability in the southwestern Atlantic , 1993 .

[38]  D. Chelton,et al.  Geosat altimeter observations of the surface circulation of the Southern Ocean , 1990 .

[39]  Pearn P. Niiler,et al.  Wind-Driven Motions in the Northeast Pacific as Measured by Lagrangian Drifters , 1995 .

[40]  S. Ramp,et al.  Moored observations of the current and temperature structure over the continental slope off central California: 2. The energetics of the flow off Point Sur , 1997 .

[41]  Gustavo Goni,et al.  Investigation of Brazil Current rings in the confluence region , 2006 .

[42]  P. Niiler,et al.  Effects of instability waves in the mixed layer of the equatorial Pacific , 1997 .

[43]  P. Niiler,et al.  The energetic surface circulation patterns of the Japan/East Sea , 2005 .

[44]  A. Orsi,et al.  On the meridional extent and fronts of the Antarctic Circumpolar Current , 1995 .

[45]  S. Rintoul,et al.  Eddy Variability and Energetics from Direct Current Measurements in the Antarctic Circumpolar Current South of Australia , 2000 .

[46]  P. Niiler.  Chapter 4.1 The world ocean surface circulation , 2001 .

[47]  W. Johns,et al.  Western boundary currents , 1995 .

[48]  L. Stramma,et al.  Upper-level circulation in the South Atlantic Ocean , 1991 .

[49]  J. Pedlosky.  Geophysical Fluid Dynamics , 1979 .

[50]  Baroclinic instability in two layer systems , 1963 .

[51]  A. Biastoch,et al.  The Role of Mesoscale Eddies in the Source Regions of the Agulhas Current , 1999 .

[52]  A. E. Gill,et al.  Energy partition in the large-scale ocean circulation and the production of mid-ocean eddies , 1974 .

[53]  Donald V. Hansen,et al.  Temporal Sampling Requirements for Surface Drifting Buoys in the Tropical Pacific , 1989 .

[54]  Matthew H. England,et al.  On the water masses and mean circulation of the South Atlantic Ocean , 1999 .

[55]  Dongxiao Zhang,et al.  Mean transport and seasonal cycle of the Kuroshio east of Taiwan with comparison to the Florida Current , 2001 .

[56]  B. Brügge.  Near‐surface mean circulation and kinetic energy in the central North Atlantic from drifter data , 1995 .

[57]  T. Müller,et al.  Direct measurements of western boundary currents off Brazil between 20°S and 28°S , 1998 .

[58]  W. Brechner Owens,et al.  A statistical description of the mean circulation and eddy variability in the northwestern Atlantic using SOFAR floats , 1991 .

[59]  J. G. Charney,et al.  THE DYNAMICS OF LONG WAVES IN A BAROCLINIC WESTERLY CURRENT , 1947 .

[60]  Roberto Fioravanti Carelli Fontes,et al.  Is the meander growth in the Brazil Current system off Southeast Brazil due to baroclinic instability , 2008 .

[61]  B. Qiu,et al.  25-Day Period Large-Scale Oscillations in the Argentine Basin Revealed by the TOPEX/POSEIDON Altimeter , 2001 .

[62]  William J. Emery,et al.  Data Analysis Methods in Physical Oceanography , 1998 .

[63]  A. Piola,et al.  Some aspects of the surface circulation south of 20°S revealed by First GARP Global Experiment Drifters , 1987 .

[64]  M. M. Mata,et al.  A circulação oceânica de larga-escala na região oeste do Atlântico Sul com base no modelo de circulação Global OCCAM , 2006 .

[65]  M. Hall.  Energetics of the Kuroshio Extension at 35°N, 152°E , 1991 .

[66]  Gustavo Goni,et al.  Investigation of the Brazil Current front variability from altimeter data , 2001 .