• Biastoch, A., and W. Krauss, 1999: The role of mesoscale eddies in the source regions of the Agulhas Current. J. Phys. Oceanogr., 29 , 23032317.

    • Search Google Scholar
    • Export Citation
  • de Ruijter, W. P. M., A. Biastoch, S. S. Drijfout, J. R. E. Lutjeharms, R. P. Matano, T. Pichevin, P. J. Van Leeuwen, and W. Weijer, 1999a: Indian–Atlantic interocean exchange: Dynamics, estimation and impact. J. Geophys. Res., 104 , 2088520910.

    • Search Google Scholar
    • Export Citation
  • de Ruijter, W. P. M., P. J. van Leeuwen, and J. R. E. Lutjeharms, 1999b: Generation and evolution of Natal Pulses: Solitary meanders in the Agulhas Current. J. Phys. Oceanogr., 29 , 30433055.

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

    • Search Google Scholar
    • Export Citation
  • Feron, R. V. C., W. P. M. de Ruijter, and D. Oksam, 1992: Ring shedding in the Agulhas Current system. J. Geophys. Res., 97 , 94679477.

    • Search Google Scholar
    • Export Citation
  • Goni, G. J., S. L. Garzoli, A. J. Roubicek, D. B. Olson, and O. B. Brown, 1997: Agulhas ring dynamics from TOPEX/POSEIDON satellite altimeter data. J. Mar. Res., 55 , 861883.

    • Search Google Scholar
    • Export Citation
  • Gründlingh, M. L., 1979: Observation of a large meander in the Agulhas Current. J. Geophys. Res., 84 , 37763778.

  • Gründlingh, M. L., . 1983: Eddies in the Southern Indian Ocean and Agulhas Current. Eddies in Marine Science, A. R. Robinson, Ed., Springer-Verlag, 245–264.

    • Search Google Scholar
    • Export Citation
  • Gründlingh, M. L., . 1985: An intense cyclonic eddy east of the Mozambique Ridge. J. Geophys. Res., 90 , 71637167.

  • Kummerow, C., W. Barnes, K. Toshiaki, J. Shiue, and J. Simpson, 1998: The Tropical Rainfall Measuring Mission (TRMM) sensor package. J. Atmos. Oceanic Technol., 15 , 809817.

    • Search Google Scholar
    • Export Citation
  • Lutjeharms, J. R. E., 1988a: Remote sensing corroboration of retroflection of the East Madagascar Current. Deep-Sea Res., 35 , 20452050.

    • Search Google Scholar
    • Export Citation
  • Lutjeharms, J. R. E., . 1988b: On the role of the East Madagascar Current as a source of the Agulhas Current. S. Afr. J. Sci., 84 , 236238.

    • Search Google Scholar
    • Export Citation
  • Lutjeharms, J. R. E., and R. C. van Ballegooyen, 1984: Topographic control in the Agulhas Current system. Deep-Sea Res., 31 , 13211337.

    • Search Google Scholar
    • Export Citation
  • Lutjeharms, J. R. E., and H. R. Roberts, 1988: The Natal pulse: An extreme transient on the Agulhas Current. J. Geophys. Res., 93 , 631645.

    • Search Google Scholar
    • Export Citation
  • Lutjeharms, J. R. E., and H. R. Valentine, 1988: Eddies at the subtropical convergence south of Africa. J. Phys. Oceanogr., 18 , 761774.

    • Search Google Scholar
    • Export Citation
  • Lutjeharms, J. R. E., and R. C. van Ballegooyen, 1988: The Retroflection of the Agulhas Current. J. Phys. Oceanogr., 18 , 15701583.

  • Lutjeharms, J. R. E., O. Boebel, P. C. F. van der Vaart, W. P. M. de Ruijter, T. Rossby, and H. L. Bryden, 2001: Evidence that the Natal pulse involves the Agulhas Current to its full depth. Geophys. Res. Lett., 28 , 34993452.

    • Search Google Scholar
    • Export Citation
  • Olson, D. B., and R. H. Evans, 1986: Rings of the Agulhas Current. Deep-Sea Res., 33 , 2742.

  • Quartly, G. D., and M. A. Srokosz, 1993: Seasonal variations in the region of the Agulhas Retroflection: Studies with Geosat and FRAM. J. Phys. Oceanogr., 23 , 21082124.

    • Search Google Scholar
    • Export Citation
  • Schouten, M. W., W. P. M. de Ruijter, P. J. van Leeuwen, and J. R. E. Lutjeharms, 2000: Translation, decay and splitting of Agulhas rings in the southeastern Atlantic Ocean. J. Geophys. Res., 105 , 2191321925.

    • Search Google Scholar
    • Export Citation
  • Van Leeuwen, P. J., W. P. M. de Ruijter, and J. R. E. Lutjeharms, 2000: Natal pulses and the formation of Agulhas rings. J. Geophys. Res., 105 , 64256436.

    • Search Google Scholar
    • Export Citation
  • Walker, N. D., and R. D. Mey, 1988: Ocean/atmosphere heat fluxes within the Agulhas Retroflection region. J. Geophys. Res., 93 , 1547515483.

    • Search Google Scholar
    • Export Citation
  • Wentz, F. J., C. Gentemann, D. Smith, and D. B. Chelton, 2000: Satellite measurements of sea surface temperature through clouds. Science, 288 , 847850.

    • Search Google Scholar
    • Export Citation
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SST Observations of the Agulhas and East Madagascar Retroflections by the TRMM Microwave Imager

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  • 1 James Rennell Division for Ocean Circulation and Climate, Southampton Oceanography Centre, Southampton, United Kingdom
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Abstract

The retroflections of the East Madagascar Current and Agulhas Current are complex rapidly evolving systems, the latter controlling the passage of warm salty water from the Indian Ocean to the Atlantic. The TRMM Microwave Imager (TMI) provides frequent observations of sea surface temperature through clouds, allowing one to monitor the evolution of these systems. The authors develop a simple feature-tracking system that obviates the need for user intervention, and use its results to guide more focused studies. In the period 1997–99, westward progradation of the Agulhas retroflection (associated with ring shedding) is observed about eight times per year, agreeing with previous estimates from infrared data, and many rings move westward or northwestward. However, this behavior is seen to change in the 2000–01 time period, with the Agulhas retroflection occurring farther to the east. A few Natal pulses are seen, but cannot be linked conclusively to the spawning of rings due to TMI's limited latitudinal coverage. The majority of features originating at the East Madagascar retroflection appear to migrate southwestward. A new observation from the data is that, although the first northward meander of the Agulhas Return Current is constrained by bathymetry, its position does vary intermittently, remaining fixed in a given location for up to six months at a time. Southward propagation of features is noted along two ridges: although eddies have been found before along the eastern slope of the Mozambique Ridge, the new results for the Madagascar Ridge indicate an extra pathway for the eddies. Eddylike features are also found leading from the Agulhas Return Current back toward the Agulhas Current. The narrow “corridor” of these features suggests that it is controlled by the gyre recirculation in the southwest Indian Ocean.

Corresponding author address: Dr. Graham D. Quartly, James Rennell Division for Ocean Circulation, Southampton Oceanography Centre, Empress Dock, Southampton SO14 3ZH, United Kingdom. Email: gdq@soc.soton.ac.uk

Abstract

The retroflections of the East Madagascar Current and Agulhas Current are complex rapidly evolving systems, the latter controlling the passage of warm salty water from the Indian Ocean to the Atlantic. The TRMM Microwave Imager (TMI) provides frequent observations of sea surface temperature through clouds, allowing one to monitor the evolution of these systems. The authors develop a simple feature-tracking system that obviates the need for user intervention, and use its results to guide more focused studies. In the period 1997–99, westward progradation of the Agulhas retroflection (associated with ring shedding) is observed about eight times per year, agreeing with previous estimates from infrared data, and many rings move westward or northwestward. However, this behavior is seen to change in the 2000–01 time period, with the Agulhas retroflection occurring farther to the east. A few Natal pulses are seen, but cannot be linked conclusively to the spawning of rings due to TMI's limited latitudinal coverage. The majority of features originating at the East Madagascar retroflection appear to migrate southwestward. A new observation from the data is that, although the first northward meander of the Agulhas Return Current is constrained by bathymetry, its position does vary intermittently, remaining fixed in a given location for up to six months at a time. Southward propagation of features is noted along two ridges: although eddies have been found before along the eastern slope of the Mozambique Ridge, the new results for the Madagascar Ridge indicate an extra pathway for the eddies. Eddylike features are also found leading from the Agulhas Return Current back toward the Agulhas Current. The narrow “corridor” of these features suggests that it is controlled by the gyre recirculation in the southwest Indian Ocean.

Corresponding author address: Dr. Graham D. Quartly, James Rennell Division for Ocean Circulation, Southampton Oceanography Centre, Empress Dock, Southampton SO14 3ZH, United Kingdom. Email: gdq@soc.soton.ac.uk

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