• Anderson, D. L. T., and P. Killworth, 1977: Spin-up of a stratified ocean, with topography. Deep-Sea Res., 24 , 709732.

  • Anderson, D. L. T., and R. A. Corry, 1985: Seasonal transport variations in the Florida Straits: A model study. J. Phys. Oceanogr., 15 , 773786.

    • Search Google Scholar
    • Export Citation
  • Barnier, B., 1988: Numerical study on the influence of the Mid-Atlantic Ridge on nonlinear first-mode baroclinic Rossby waves generated by seasonal winds. J. Phys. Oceanogr., 18 , 417433.

    • Search Google Scholar
    • Export Citation
  • Gerdes, R., and C. Wübber, 1991: Seasonal variability of the North Atlantic Ocean—A model intercomparison. J. Phys. Oceanogr., 21 , 13001322.

    • Search Google Scholar
    • Export Citation
  • Gill, A. E., and P. P. Niiler, 1973: The theory of the seasonal variability in the ocean. Deep-Sea Res., 20 , 141177.

  • Greatbatch, R. J., and A. Goulding, 1989: Seasonal variations in a linear barotropic model of the North Atlantic driven by the Hellerman and Rosenstein wind stress field. J. Phys. Oceanogr., 19 , 572595.

    • Search Google Scholar
    • Export Citation
  • Greatbatch, R. J., and A. Goulding, . 1990: On the seasonal variation of transport through the Tokara Strait. J. Oceanogr. Soc. Japan, 46 , 920.

    • Search Google Scholar
    • Export Citation
  • Hasunuma, K., and K. Yoshida, 1978: Splitting of the subtropical gyre in the western North Pacific. J. Oceanogr. Soc. Japan, 37 , 160172.

    • Search Google Scholar
    • Export Citation
  • Hong, B. G., W. Sturges, and A. J. Clarke, 2000: Sea level on the U.S. East Coast: Decadal variability caused by open ocean wind-curl forcing. J. Phys. Oceanogr., 30 , 20882098.

    • Search Google Scholar
    • Export Citation
  • Ichikawa, H., and R. C. Beardsley, 1993: Temporal and spatial variability of volume transport of the Kuroshio in the East China Sea. Deep-Sea Res., 40 , 583605.

    • Search Google Scholar
    • Export Citation
  • Ichikawa, H., and M. Chaen, 2000: Seasonal variation of heat and freshwater transports by the Kuroshio in the East China Sea. J. Mar. Sys., 24 , 119129.

    • Search Google Scholar
    • Export Citation
  • Imawaki, S., H. Uchida, H. Ichikawa, M. Fukasawa, and S. Umatani, and ASUKA Group, 1997: Time series of the Kuroshio transport derived from field observation and altimetry data. International WOCE Newsletter, Vol. 25,. 1518.

    • Search Google Scholar
    • Export Citation
  • Imawaki, S., H. Uchida, H. Ichikawa, M. Fukasawa, and S. Umatani, . 2001: Satellite altimeter monitoring the Kuroshio transport south of Japan. Geophys. Res. Lett., 28 , 1720.

    • Search Google Scholar
    • Export Citation
  • Isobe, A., 2000: Two-layer model on the branching of the Kuroshio southwest of Kyushu, Japan. J. Phys. Oceanogr., 30 , 24612476.

  • Jarvis, R. A., and G. Veronis, 1994: Strong deep recirculations in a two-layer wind driven ocean. J. Phys. Oceanogr., 24 , 759776.

  • Kagimoto, T., and T. Yamagata, 1997: Seasonal transport variations of the Kuroshio: An OGCM simulation. J. Phys. Oceanogr., 27 , 403418.

    • Search Google Scholar
    • Export Citation
  • Kubota, M., H. Yokota, and T. Okamoto, 1995: Mechanism of the seasonal transport variation through the Tokara Strait. J. Oceanogr., 51 , 441458.

    • Search Google Scholar
    • Export Citation
  • Large, W. G., and S. Pond, 1981: Open ocean momentum flux measurements in moderate to strong winds,. J. Phys. Oceanogr., 11 , 324336.

  • Molinari, R. L., W. D. Wilson, and K. D. Leaman, 1985: Volume and heat transports of the Florida Current: April 1982 to August 1983. Science, 227 , 295297.

    • Search Google Scholar
    • Export Citation
  • Niiler, P. P., and W. S. Richardson, 1973: Seasonal variability of the Florida Current. J. Mar. Res., 31 , 144167.

  • Rhines, P. B., and W. R. Young, 1982: A theory of wind-driven circulation. I.Mid-ocean gyres. J. Mar. Res., 40 , (Suppl.),. 559596.

  • Rooth, C., H. Stommel, and G. Veronis, 1978: On motions in steady, layered, geostrophic models. J. Oceanogr. Soc. Japan, 34 , 265267.

  • Sato, O. T., and T. Rossby, 1995: Seasonal and low frequency variations in dynamic height anomaly and transport of the Gulf Stream. Deep-Sea Res., 42 , 149164.

    • Search Google Scholar
    • Export Citation
  • Schott, F. A., and R. J. Zantopp, 1985: On the seasonal and interannual variability of the Florida Current: Seasonal and interannual variability. Science, 227 , 308311.

    • Search Google Scholar
    • Export Citation
  • Sekine, Y., and K. Kutsuwada, 1994: Seasonal variation in volume transport of the Kuroshio south of Japan. J. Phys. Oceanogr., 24 , 261272.

    • Search Google Scholar
    • Export Citation
  • Sturges, W., and B. G. Hong, 1995: Wind forcing of the Atlantic thermocline along 32°N at low frequencies. J. Phys. Oceanogr., 25 , 17061715.

    • Search Google Scholar
    • Export Citation
  • Sturges, W., B. G. Hong, and A. J. Clarke, 1998: Decadal wind forcing of the North Atlantic subtropical gyre. J. Phys. Oceanogr., 28 , 659668.

    • Search Google Scholar
    • Export Citation
  • Thompson, K. R., J. R. N. Lazier, and B. Taylor, 1986: Wind-forced changes in Labrador Current transport. J. Geophys. Res., 91 , 1426114268.

    • Search Google Scholar
    • Export Citation
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Annual Variation of the Kuroshio Transport in a Two-Layer Numerical Model with a Ridge

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  • 1 Department of Earth System Science and Technology, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka, Japan
  • | 2 Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka, Japan
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Abstract

A two-layer numerical model driven by the wind stress is used to explain the observed annual variation of the Kuroshio transport south of Japan. Special attention is given to the effect of a ridge, representing the Izu–Ogasawara Ridge, on the generation of the baroclinic activity through the coupling of the barotropic and baroclinic modes of motion. For annual variation, lower-layer motion is found in areas surrounding the ridge because isostasy (a state of no motion in the lower layer) is not achieved within such a short timescale. Thus, the lower-layer flow impinges on the bottom slope. This impinging process generates anomalies of the upper-layer thickness especially on the eastern side of the ridge. Thereafter, anomalies move westward with characteristic velocities composed of the vertically averaged flow and westward propagation of the long baroclinic Rossby wave forced above the ridge. As anomalies of the upper-layer thickness move westward above the ridge, isostasy is accomplished with respect to these anomalies. As a result, the positive (negative) anomaly of the upper-layer thickness carries the information about the positive (negative) anomaly of the volume transport as it reaches the western edge of the ridge. Thereafter, anomalies of the volume transport are released to the west of the ridge. This experiment shows that the annual range of the volume transport east of the ridge is around 40 Sv, which is nearly equal to the zonal integration of the Sverdrup transport there. The annual range west of the ridge, however, reduces to around 10 Sv, which is mostly caused by the baroclinic activity generated above the ridge. Results are compared with the observed Kuroshio transport across the ASUKA line south of Japan. The annual range west of the ridge is consistent with that estimated from the observation.

Corresponding author address: Dr. Atsuhiko Isobe, Department of Earth System Science and Technology, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1, Kasuga-Koen, Kasuga, Fukuoka 816-8580, Japan. Email: isobe@esst.kyushu-u.ac.jp

Abstract

A two-layer numerical model driven by the wind stress is used to explain the observed annual variation of the Kuroshio transport south of Japan. Special attention is given to the effect of a ridge, representing the Izu–Ogasawara Ridge, on the generation of the baroclinic activity through the coupling of the barotropic and baroclinic modes of motion. For annual variation, lower-layer motion is found in areas surrounding the ridge because isostasy (a state of no motion in the lower layer) is not achieved within such a short timescale. Thus, the lower-layer flow impinges on the bottom slope. This impinging process generates anomalies of the upper-layer thickness especially on the eastern side of the ridge. Thereafter, anomalies move westward with characteristic velocities composed of the vertically averaged flow and westward propagation of the long baroclinic Rossby wave forced above the ridge. As anomalies of the upper-layer thickness move westward above the ridge, isostasy is accomplished with respect to these anomalies. As a result, the positive (negative) anomaly of the upper-layer thickness carries the information about the positive (negative) anomaly of the volume transport as it reaches the western edge of the ridge. Thereafter, anomalies of the volume transport are released to the west of the ridge. This experiment shows that the annual range of the volume transport east of the ridge is around 40 Sv, which is nearly equal to the zonal integration of the Sverdrup transport there. The annual range west of the ridge, however, reduces to around 10 Sv, which is mostly caused by the baroclinic activity generated above the ridge. Results are compared with the observed Kuroshio transport across the ASUKA line south of Japan. The annual range west of the ridge is consistent with that estimated from the observation.

Corresponding author address: Dr. Atsuhiko Isobe, Department of Earth System Science and Technology, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1, Kasuga-Koen, Kasuga, Fukuoka 816-8580, Japan. Email: isobe@esst.kyushu-u.ac.jp

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