• Azevedo, J. L. L., , D. Nof, , and M. M. Mata, 2012: Eddy-train encounters with a continental boundary: A South Atlantic case study. J. Phys. Oceanogr., 42, 15481565, doi:10.1175/JPO-D-11-027.1.

    • Search Google Scholar
    • Export Citation
  • Beal, L. M., 2009: A time series of Agulhas Undercurrent transport. J. Phys. Oceanogr., 39, 24362450, doi:10.1175/2009JPO4195.1.

  • Beal, L. M., , and H. L. Bryden, 1997: Observations of an Agulhas Undercurrent. Deep-Sea Res. I, 44, 17151724, doi:10.1016/S0967-0637(97)00033-2.

    • Search Google Scholar
    • Export Citation
  • Beal, L. M., , and H. L. Bryden, 1999: The velocity and vorticity structure of the Agulhas Current at 32°S. J. Geophys. Res., 104, 51515176, doi:10.1029/1998JC900056.

    • Search Google Scholar
    • Export Citation
  • Beal, L. M., and et al. , 2011: On the role of the Agulhas system in ocean circulation and climate. Nature, 472, 429436, doi:10.1038/nature09983.

    • Search Google Scholar
    • Export Citation
  • Beal, L. M., , S. Elipot, , A. Houk, , and G. M. Leber, 2015: Capturing the transport variability of a western boundary jet: Results from the Agulhas Current Time-Series Experiment (ACT). J. Phys. Oceanogr., 45, 13021324, doi:10.1175/JPO-D-14-0119.1.

    • Search Google Scholar
    • Export Citation
  • Beron-Vera, F. J., , M. J. Olascoaga, , and G. J. Goni, 2008: Oceanic mesoscale eddies as revealed by Lagrangian coherent structures. Geophys. Res. Lett., 35, L12603, doi:10.1029/2008GL033957.

    • Search Google Scholar
    • Export Citation
  • Carter, E. F., , and A. R. Robinson, 1987: Analysis models for the estimation of oceanic fields. J. Atmos. Oceanic Technol., 4, 4974, doi:10.1175/1520-0426(1987)004<0049:AMFTEO>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Chapman, P., , S. F. DiMarco, , R. E. Davis, , and A. C. Coward, 2003: Flow at intermediate depths around Madagascar based on ALACE float trajectories. Deep-Sea Res. II, 50, 19571986, doi:10.1016/S0967-0645(03)00040-7.

    • Search Google Scholar
    • Export Citation
  • Chen, Z., , L. Wu, , B. Qiu, , S. Sun, , and F. Jia, 2014: Seasonal variation of the South Equatorial Current bifurcation off Madagascar. J. Phys. Oceanogr., 44, 618631, doi:10.1175/JPO-D-13-0147.1.

    • Search Google Scholar
    • Export Citation
  • da Silveira, I. C. A., , L. Calado, , B. M. Castro, , M. Cirano, , J. A. M. Lima, , and A. S. Mascarenhas, 2004: On the baroclinic structure of the Brazil Current–intermediate western boundary current system at 22°–23°S. Geophys. Res. Lett., 31, L14308, doi:10.1029/2004GL020036.

    • Search Google Scholar
    • Export Citation
  • de Ruijter, W. P. M., , A. Biastoch, , S. S. Drijfhout, , J. R. E. Lutjeharms, , R. P. Matano, , T. Pichevin, , P. J. van Leeuwen, , and W. Weijer, 1999: Indian-Atlantic interocean exchange: Dynamics, estimation and impact. J. Geophys. Res., 104, 20 88520 910, doi:10.1029/1998JC900099.

    • Search Google Scholar
    • Export Citation
  • de Ruijter, W. P. M., , H. Ridderinkhof, , J. R. E. Lutjeharms, , M. W. Schouten, , and C. Veth, 2002: Observations of the flow in the Mozambique Channel. Geophys. Res. Lett., 29, doi:10.1029/2001GL013714.

    • Search Google Scholar
    • Export Citation
  • de Ruijter, W. P. M., , H. M. van Aken, , E. J. Beier, , J. R. E. Lutjeharms, , R. P. Matano, , and M. W. Schouten, 2004: Eddies and dipoles around South Madagascar: Formation, pathways and large-scale impact. Deep-Sea Res. I, 51, 383400, doi:10.1016/j.dsr.2003.10.011.

    • Search Google Scholar
    • Export Citation
  • de Ruijter, W. P. M., , H. Ridderinkhof, , and M. W. Schouten, 2005: Variability of the southwest Indian Ocean. Philos. Trans. Roy. Soc. London, A363, 6376, doi:10.1098/rsta.2004.1478.

    • Search Google Scholar
    • Export Citation
  • DiMarco, S. F., , P. Chapman, , W. D. Nowlin Jr., , P. Hacker, , K. Donohue, , M. Luther, , G. C. Johnson, , and J. Toole, 2002: Volume transport and property distributions of the Mozambique Channel. Deep-Sea Res. II, 49, 14811511, doi:10.1016/S0967-0645(01)00159-X.

    • Search Google Scholar
    • Export Citation
  • Duncan, C. P., 1970: The Agulhas Current. Ph.D. thesis, University of Hawaii, 76 pp.

  • Faghmous, J. H., , I. Frenger, , Y. Yao, , R. Warmka, , A. Lindell, , and V. Kumar, 2015: A daily global mesoscale ocean eddy dataset from satellite altimetry. Sci. Data, 2, 150028, doi:10.1038/sdata.2015.28.

    • Search Google Scholar
    • Export Citation
  • Fomin, L. M., 1964: The Dynamic Method in Oceanography.Elsevier, 211 pp.

  • Gordon, A. L., , R. Weiss, , W. M. Smethie Jr., , and M. J. Warner, 1992: Thermocline and intermediate water communication between the South Atlantic and Indian Oceans. J. Geophys. Res., 97, 72237240, doi:10.1029/92JC00485.

    • Search Google Scholar
    • Export Citation
  • Gründlingh, M. L., 1993: On the winter flow in the southern Mozambique Channel. Deep-Sea Res. I, 40, 409418, doi:10.1016/0967-0637(93)90011-Q.

    • Search Google Scholar
    • Export Citation
  • Haller, G., 2002: Lagrangian coherent structures from approximate velocity data. Phys. Fluids, 14, 18511861, doi:10.1063/1.1477449.

  • Haller, G., 2005: An objective definition of a vortex. J. Fluid Mech., 525, 126, doi:10.1017/S0022112004002526.

  • Harris, T. F. W., 1972: Sources of the Agulhas Current in the spring of 1964. Deep-Sea Res. Oceanogr. Abstr., 19, 633650, doi:10.1016/0011-7471(72)90091-5.

    • Search Google Scholar
    • Export Citation
  • Kundu, P. K., , and I. M. Cohen, 2008: Fluid Mechanics.Academic Press, 878 pp.

  • Lutjeharms, J. R. E., 1988: Remote sensing corroboration of retroflection of the East Madagascar Current. Deep-Sea Res., 35A, 20452050, doi:10.1016/0198-0149(88)90124-0.

    • Search Google Scholar
    • Export Citation
  • Lutjeharms, J. R. E., 2006: The Agulhas Current.Springer, 329 pp.

  • Lutjeharms, J. R. E., , N. D. Bang, , and C. P. Duncan, 1981: Characteristics of the currents east and south of Madagascar. Deep-Sea Res., 28A, 879899, doi:10.1016/0198-0149(81)90008-X.

    • Search Google Scholar
    • Export Citation
  • Matano, R. P., , E. J. Beier, , P. T. Strub, , and R. Tokmakian, 2002: Large-scale forcing of the Agulhas variability: The seasonal cycle. J. Phys. Oceanogr., 32, 12281241, doi:10.1175/1520-0485(2002)032<1228:LSFOTA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Nauw, J. J., , H. M. van Aken, , A. Webb, , J. R. E. Lutjeharms, , and W. P. M. de Ruijter, 2008: Observations of the southern East Madagascar Current and undercurrent and countercurrent system. J. Geophys. Res., 113, C08006, doi:10.1029/2007JC004639.

    • Search Google Scholar
    • Export Citation
  • New, A. L., , S. G. Anderson, , D. A. Smeed, , and K. L. Stansfield, 2007: On the circulation of water masses across the Mascarene Plateau in the south Indian Ocean. Deep-Sea Res. I, 54, 4274, doi:10.1016/j.dsr.2006.08.016.

    • Search Google Scholar
    • Export Citation
  • Olson, D. B., , and R. H. Evans, 1986: Rings of the Agulhas Current. Deep-Sea Res., 33A, 2742, doi:10.1016/0198-0149(86)90106-8.

  • Palastanga, V., , P. J. van Leeuwen, , and W. P. M. de Ruijter, 2006: A link between low-frequency mesoscale eddy variability around Madagascar and the large-scale Indian Ocean variability. J. Geophys. Res., 111, C09029, doi:10.1029/2005JC003081.

    • Search Google Scholar
    • Export Citation
  • Palastanga, V., , P. J. van Leeuwen, , M. W. Schouten, , and W. P. M. de Ruijter, 2007: Flow structure and variability in the subtropical Indian Ocean: Instability of the South Indian Ocean Countercurrent. J. Geophys. Res., 112, C01001, doi:10.1029/2005JC003395.

    • Search Google Scholar
    • Export Citation
  • Polito, P. S., , and O. Sato, 2015: Do eddies ride on Rossby waves? J. Geophys. Res., 120, 54175435, doi:10.1002/2015JC010737.

  • Ponsoni, L., , B. Aguiar-González, , L. R. M. Maas, , H. M. van Aken, , and H. Ridderinkhof, 2015a: Long-term observations of the East Madagascar Undercurrent. Deep-Sea Res. I, 100, 6478, doi:10.1016/j.dsr.2015.02.004.

    • Search Google Scholar
    • Export Citation
  • Ponsoni, L., , B. Aguiar-González, , J. J. Nauw, , H. Ridderinkhof, , and L. R. M. Maas, 2015b: First observational evidence of a North Madagascar Undercurrent. Dyn. Atmos. Oceans, 72, 1220, doi:10.1016/j.dynatmoce.2015.08.002.

    • Search Google Scholar
    • Export Citation
  • Quartly, G. D., , J. J. H. Buck, , and M. A. Srokosz, 2005: Eddy variability east of Madagascar. Philos. Trans. Roy. Soc. London, A363, 7779, doi:10.1098/rsta.2004.1479.

    • Search Google Scholar
    • Export Citation
  • Quartly, G. D., , J. J. H. Buck, , M. A. Srokosz, , and A. C. Coward, 2006: Eddies around Madagascar—The retroflection re-considered. J. Mar. Syst., 63, 115129, doi:10.1016/j.jmarsys.2006.06.001.

    • Search Google Scholar
    • Export Citation
  • Ridderinkhof, H., , and W. P. M. de Ruijter, 2003: Moored current observations in the Mozambique Channel. Deep-Sea Res. II, 50, 19331955, doi:10.1016/S0967-0645(03)00041-9.

    • Search Google Scholar
    • Export Citation
  • Ridderinkhof, H., , P. M. van der Werf, , J. E. Ullgren, , H. M. van Aken, , P. J. van Leeuwen, , and W. P. M. de Ruijter, 2010: Seasonal and interannual variability in the Mozambique Channel from moored current observations. J. Geophys. Res., 115, C06010, doi:10.1029/2009JC005619.

    • Search Google Scholar
    • Export Citation
  • Ridderinkhof, W., , D. Le Bars, , A. S. von der Heydt, , and W. P. M. de Ruijter, 2013: Dipoles of the South East Madagascar Current. Geophys. Res. Lett., 40, 558562, doi:10.1002/grl.50157.

    • Search Google Scholar
    • Export Citation
  • Rio, M.-H., , S. Mulet, , and N. Picot, 2014: Beyond GOCE for the ocean circulation estimate: Synergetic use of altimetry, gravimetry, and in situ data provides new insight into geostrophic and Ekman currents. Geophys. Res. Lett., 41, 89188925, doi:10.1002/2014GL061773.

    • Search Google Scholar
    • Export Citation
  • Samelson, R. M., 2013: Lagrangian motion, coherent structures, and lines of persistent material strain. Annu. Rev. Mar. Sci., 5, 137163, doi:10.1146/annurev-marine-120710-100819.

    • Search Google Scholar
    • Export Citation
  • Schott, F., , M. Fieux, , J. Kindle, , J. Swallow, , and R. Zantopp, 1988: The boundary currents east and north of Madagascar: 2. Direct measurements and model comparisons. J. Geophys. Res., 93, 49634974, doi:10.1029/JC093iC05p04963.

    • Search Google Scholar
    • Export Citation
  • Schott, F., , S.-P. Xie, , and J. P. McCreary Jr., 2009: Indian Ocean circulation and climate variability. Rev. Geophys., 47, RG1002, doi:10.1029/2007RG000245.

    • Search Google Scholar
    • Export Citation
  • Schouten, M. W., , W. P. M. de Ruijter, , and P. J. van Leeuwen, 2002a: Upstream control of Agulhas ring shedding. J. Geophys. Res., 107, doi:10.1029/2001JC000804.

    • Search Google Scholar
    • Export Citation
  • Schouten, M. W., , W. P. M. de Ruijter, , P. J. van Leeuwen, , and H. A. Dijkstra, 2002b: An oceanic teleconnection between the equatorial and southern Indian Ocean. Geophys. Res. Lett., 29, doi:10.1029/2001GL014542.

    • Search Google Scholar
    • Export Citation
  • Shi, C., , and D. Nof, 1993: The splitting of eddies along boundaries. J. Mar. Res., 51, 771795, doi:10.1357/0022240933223927.

  • Shi, C., , and D. Nof, 1994: The destruction of lenses and generation of wodons. J. Phys. Oceanogr., 24, 11201136, doi:10.1175/1520-0485(1994)024<1120:TDOLAG>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Siedler, G., , M. Rouault, , and J. R. E. Lutjeharms, 2006: Structure and origin of the subtropical South Indian Ocean Countercurrent. Geophys. Res. Lett., 33, L24609, doi:10.1029/2006GL027399.

    • Search Google Scholar
    • Export Citation
  • Stramma, L., , and J. R. E. Lutjeharms, 1997: The flow field of the subtropical gyre of the South Indian Ocean. J. Geophys. Res., 102, 55135530, doi:10.1029/96JC03455.

    • Search Google Scholar
    • Export Citation
  • Swallow, J., , M. Fieux, , and F. Schott, 1988: The boundary currents east and north of Madagascar: 1. Geostrophic currents and transports. J. Geophys. Res., 93, 49514962, doi:10.1029/JC093iC05p04951.

    • Search Google Scholar
    • Export Citation
  • Torrence, C., , and G. P. Compo, 1998: A practical guide to wavelet analysis. Bull. Amer. Meteor. Soc., 79, 6178, doi:10.1175/1520-0477(1998)079<0061:APGTWA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Ullgren, J. E., , H. M. van Aken, , H. Ridderinkhof, , and W. P. M. de Ruijter, 2012: The hydrography of the Mozambique Channel from six years of continuous temperature, salinity, and velocity observations. Deep-Sea Res. I, 69, 3650, doi:10.1016/j.dsr.2012.07.003.

    • Search Google Scholar
    • Export Citation
  • van Aken, H. M., , H. Ridderinkhof, , and W. P. M. de Ruijter, 2004: North Atlantic deep water in the south-western Indian Ocean. Deep-Sea Res. I, 51, 755776, doi:10.1016/j.dsr.2004.01.008.

    • Search Google Scholar
    • Export Citation
  • Warren, B. A., , T. Whitworth III, , and J. H. LaCasce, 2002: Forced resonant undulation in the deep Mascarene basin. Deep-Sea Res. II, 49, 15131526, doi:10.1016/S0967-0645(01)00151-5.

    • Search Google Scholar
    • Export Citation
  • Weijer, W., 2008: Normal modes of the Mascarene basin. Deep-Sea Res. I, 55, 128136, doi:10.1016/j.dsr.2007.10.005.

  • Wyrtki, K., 1971: Oceanographic Atlas of the International Indian Ocean Expedition.National Science Foundation, 531 pp.

  • Zhai, X., , H. L. Johnson, , and D. P. Marshall, 2010: Significant sink of ocean-eddy energy near western boundaries. Nat. Geosci., 3, 608621, doi:10.1038/ngeo943.

    • Search Google Scholar
    • Export Citation
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The East Madagascar Current: Volume Transport and Variability Based on Long-Term Observations

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  • 1 Royal Netherlands Institute for Sea Research (NIOZ), Den Burg, Texel, Netherlands
  • | 2 Royal Netherlands Institute for Sea Research (NIOZ), Den Burg, Texel, and Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, Netherlands
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Abstract

This study provides a long-term description of the poleward East Madagascar Current (EMC) in terms of its observed velocities, estimated volume transport, and variability based on both ~2.5 yr of continuous in situ measurements and ~21 yr of satellite altimeter data. An array of five moorings was deployed at 23°S off eastern Madagascar as part of the Indian–Atlantic Exchange in present and past climate (INATEX) observational program. On average, the EMC has a horizontal scale of about 60–100 km and is found from the surface to about 1000-m depth. Its time-averaged core is positioned at the surface, at approximately 20 km from the coast, with velocity of 79 (±21) cm s−1. The EMC mean volume transport is estimated to be 18.3 (±8.4) Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1). During the strongest events, maximum velocities and transport reach up to 170 cm s−1 and 50 Sv, respectively. A good agreement is found between the in situ transport estimated over the first 8 m of water column [0.32 (±0.13) Sv] with the altimetry-derived volume transport [0.28 (±0.09) Sv]. Results from wavelet analysis display a dominant nearly bimonthly (45–85 days) frequency band of transport variability, which explains about 41% of the transport variance. Altimeter data suggest that this band of variability is induced by the arrival of westward-propagating sea level anomalies, which in turn are likely represented by mesoscale cyclonic and anticyclonic eddies. Annual averages of the altimeter-derived surface transport suggest that interannual variabilities also play a role in the EMC system.

Supplemental information related to this paper is available at the Journals Online website: http://dx.doi.org/10.1175/JPO-D-15-0154.s1.

Corresponding author address: Leandro Ponsoni, NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg, Texel, Netherlands. E-mail: lponsoni@nioz.nl

Abstract

This study provides a long-term description of the poleward East Madagascar Current (EMC) in terms of its observed velocities, estimated volume transport, and variability based on both ~2.5 yr of continuous in situ measurements and ~21 yr of satellite altimeter data. An array of five moorings was deployed at 23°S off eastern Madagascar as part of the Indian–Atlantic Exchange in present and past climate (INATEX) observational program. On average, the EMC has a horizontal scale of about 60–100 km and is found from the surface to about 1000-m depth. Its time-averaged core is positioned at the surface, at approximately 20 km from the coast, with velocity of 79 (±21) cm s−1. The EMC mean volume transport is estimated to be 18.3 (±8.4) Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1). During the strongest events, maximum velocities and transport reach up to 170 cm s−1 and 50 Sv, respectively. A good agreement is found between the in situ transport estimated over the first 8 m of water column [0.32 (±0.13) Sv] with the altimetry-derived volume transport [0.28 (±0.09) Sv]. Results from wavelet analysis display a dominant nearly bimonthly (45–85 days) frequency band of transport variability, which explains about 41% of the transport variance. Altimeter data suggest that this band of variability is induced by the arrival of westward-propagating sea level anomalies, which in turn are likely represented by mesoscale cyclonic and anticyclonic eddies. Annual averages of the altimeter-derived surface transport suggest that interannual variabilities also play a role in the EMC system.

Supplemental information related to this paper is available at the Journals Online website: http://dx.doi.org/10.1175/JPO-D-15-0154.s1.

Corresponding author address: Leandro Ponsoni, NIOZ Royal Netherlands Institute for Sea Research, P.O. Box 59, 1790 AB Den Burg, Texel, Netherlands. E-mail: lponsoni@nioz.nl
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