Islands in Zonal Flow

Michael A. Spall Department of Physical Oceanography, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts

Search for other papers by Michael A. Spall in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

The impact of a meridional gradient in sea surface temperature (warm toward the equator, cold toward the pole) on the circulation around an island is investigated. The upper-ocean eastward geostrophic flow that balances such a meridional gradient is blocked where the isotherms intersect boundaries. In the case in which the boundaries represent either the eastern or western side of a planetary-scale island, circulation integrals around the island show that some of this eastward transport will flow around both the equatorward and poleward tips of the island. There is also a net downwelling along the western side of the island and a net upwelling along the eastern side of the island. An analytic model of the eastern and western boundary currents is used together with a circulation integral to estimate the fraction of the eastward transport that flows around the equatorward and poleward tips of the island and the net upwelling/downwelling on either side of the island. Calculations with a primitive equation numerical model are in close agreement with the theory. A simple closed-form analytic solution for the transport around the island tips is derived in the limit of strong buoyancy forcing. It is found that, over a wide range of parameter space, a significant fraction of the eastward transport in the upper ocean circulates around the tips of the island from the western basin into the eastern basin.

Corresponding author address: Dr. Michael A. Spall, MS 21, 360 Woods Hole Road, Woods Hole Oceanographic Institution, Woods Hole, MA 02543. Email: mspall@whoi.edu

Abstract

The impact of a meridional gradient in sea surface temperature (warm toward the equator, cold toward the pole) on the circulation around an island is investigated. The upper-ocean eastward geostrophic flow that balances such a meridional gradient is blocked where the isotherms intersect boundaries. In the case in which the boundaries represent either the eastern or western side of a planetary-scale island, circulation integrals around the island show that some of this eastward transport will flow around both the equatorward and poleward tips of the island. There is also a net downwelling along the western side of the island and a net upwelling along the eastern side of the island. An analytic model of the eastern and western boundary currents is used together with a circulation integral to estimate the fraction of the eastward transport that flows around the equatorward and poleward tips of the island and the net upwelling/downwelling on either side of the island. Calculations with a primitive equation numerical model are in close agreement with the theory. A simple closed-form analytic solution for the transport around the island tips is derived in the limit of strong buoyancy forcing. It is found that, over a wide range of parameter space, a significant fraction of the eastward transport in the upper ocean circulates around the tips of the island from the western basin into the eastern basin.

Corresponding author address: Dr. Michael A. Spall, MS 21, 360 Woods Hole Road, Woods Hole Oceanographic Institution, Woods Hole, MA 02543. Email: mspall@whoi.edu

Save
  • Bleck, R., C. Rooth, D. Hu, and L. T. Smith, 1992: Salinity-driven thermocline transients in a wind- and thermohaline-forced isopycnal coordinate model of the North Atlantic. J. Phys. Oceanogr., 22 , 14861505.

    • Search Google Scholar
    • Export Citation
  • Davey, M. K., 1983: A two-level model of a thermally forced ocean basin. J. Phys. Oceanogr., 13 , 169190.

  • Ffield, A., K. Vranes, A. L. Gordon, and R. D. Susanto, 2000: Temperature variability within Makassar Strait. Geophys. Res. Lett., 27 , 237240.

    • Search Google Scholar
    • Export Citation
  • Firing, E., B. Qiu, and W. Miao, 1999: Time-dependent island rule and its application to the time-varying North Hawaiian Ridge Current. J. Phys. Oceanogr., 29 , 26712688.

    • Search Google Scholar
    • Export Citation
  • Godfrey, J. S., 1989: A Sverdrup model of the depth-integrated flow for the World Ocean, allowing for island circulations. Geophys. Astrophys. Fluid Dyn., 45 , 89112.

    • Search Google Scholar
    • Export Citation
  • Godfrey, J. S., 1996: The effect of the Indonesian Throughflow on ocean circulation and heat exchange with the atmosphere: A review. J. Geophys. Res., 101 , 1221712237.

    • Search Google Scholar
    • Export Citation
  • Godfrey, J. S., and K. R. Ridgway, 1985: The large-scale environment of the poleward-flowing Leeuwin Current, Western Australia: Longshore steric height gradients, wind stresses, and geostrophic flow. J. Phys. Oceanogr., 15 , 481495.

    • Search Google Scholar
    • Export Citation
  • Godfrey, J. S., and A. J. Weaver, 1991: Is the Leeuwin Current driven by Pacific heating and winds? Progress in Oceanography, Vol. 27, Pergamon, 225–272.

    • Search Google Scholar
    • Export Citation
  • Godfrey, J. S., and Y. Masumoto, 1999: Diagnosing the mean strength of the Indonesian Throughflow in an ocean general circulation model. J. Geophys. Res., 104 , 78897895.

    • Search Google Scholar
    • Export Citation
  • Gordon, A. L., 1986: Interocean exchange of thermocline water. J. Geophys. Res., 91 , 50375046.

  • Gordon, A. L., R. D. Susanto, and A. Ffield, 1999: Throughflow within Makassar Strait. Geophys. Res. Lett., 26 , 33253328.

  • Kawase, M., 1987: Establishment of deep ocean circulation driven by deep-water production. J. Phys. Oceanogr., 17 , 22942317.

  • Killworth, P. D., D. B. Chelton, and R. A. de Szoeke, 1997: The speed of observed and theoretical long extratropical planetary waves. J. Phys. Oceanogr., 27 , 19461966.

    • Search Google Scholar
    • Export Citation
  • McCreary, J. P., 1981: A linear stratified ocean model of the coastal undercurrent. Philos. Trans. Roy. Soc. London, A302. 385413.

  • McCreary, J. P., S. R. Shetye, and P. K. Kundu, 1986: Thermohaline forcing of eastern boundary currents: With application to the circulation off the west coast of Australia. J. Mar. Res., 44 , 7192.

    • Search Google Scholar
    • Export Citation
  • McCreary, J. P., Y. Fukamachi, and P. Lu, 1992: A nonlinear mechanism for maintaining coastally trapped eastern boundary currents. J. Geophys. Res., 97 , 56775692.

    • Search Google Scholar
    • Export Citation
  • Munk, W. H., 1950: On the wind-driven ocean circulation. J. Meteor., 7 , 7993.

  • Pedlosky, J., and M. A. Spall, 1999: Rossby normal modes in basins with barriers. J. Phys. Oceanogr., 29 , 23322349.

  • Pedlosky, J., L. J. Pratt, M. A. Spall, and K. R. Helfrich, 1997: Circulation around islands and ridges. J. Mar. Res., 55 , 11991251.

  • Pratt, L. J., and J. Pedlosky, 1998: Barotropic circulation around islands with friction. J. Phys. Oceanogr., 28 , 21482162.

  • Spall, M. A., 2000: Buoyancy-forced circulations around islands and ridges. J. Mar. Res., 58 , 957982.

  • Thompson, R. O. R. Y., 1987: Continental-shelf-scale model of the Leeuwin Current. J. Mar. Res., 45 , 813827.

  • Wajsowicz, R. C., 1993: The circulation of the depth-integrated flow around an island with application to the Indonesian Throughflow. J. Phys. Oceanogr., 23 , 14701484.

    • Search Google Scholar
    • Export Citation
  • Wajsowicz, R. C., 1995: The response of the Indo–Pacific Throughflow to interannual variations in the Pacific wind stress. Part I: Idealized geometry and variations. J. Phys. Oceanogr., 25 , 18051826.

    • Search Google Scholar
    • Export Citation
  • Weaver, A. J., and J. H. Middleton, 1990: An analytic model for the Leeuwin Current off western Australia. Cont. Shelf Res., 10 , 105122.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 232 33 6
PDF Downloads 40 18 2