Abstract
To better understand the mechanism underlying the variation of the Kuroshio south of central Japan, we have examined the variability of current structure in its upstream region, southeast of Amami-Ohshima Island in the northern Ryukyu Islands. By combined use of ship-mounted Acoustic Doppler Current Profiler (ADCP) and the TOPEX/POSEIDON satellite altimeter data on Path 214, the sea surface absolute geostrophic currents were estimated every ten days from January 1998 to July 2002. The 4.5-year mean surface current was found to flow northeastward north of 26.8°N with a maximum speed of 14 cm s−1 over the shelf slope at 3000 m depth. The moored current-meter observations at three or four mooring stations from Dec. 1998 to Oct. 2002 suggested the existence of a northeastward undercurrent with a maximum core velocity of 23 cm s−1 at 600 m depth over the shelf slope at 1600 m depth. The mean volume transport in the top 1500 m between 27.9°N and 26.7°N is estimated to be 16 × 106 m3s−1 northeastward, including the subsurface core current related component of 4 × 106 m3s−1.
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References
Hsueh, Y., J. R. Schultz and W. R. Holland (1997): The Kuroshio flow-through in the East China Sea: A numerical model. Prog. Oceanogr., 39, 79–108.
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, 583–605.
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, 119–129.
Ichikawa, H., H. Nakamura and A. Nishina (2000): Strong northeastward current outside of the East China Sea. In Proceedings of the 5th Pacific Ocean Remote Sensing Conference, ed. by E. Desa, PORSEC Secretariat, (Indian) National Institute of Oceanography, Goa, 1, p. 284–288.
Imawaki, S., H. Uchida, H. Ichikawa, M. Fukasawa, S. Umatani and ASUKA Group (2001): Satellite altimeter monitoring the Kuroshio transport south of Japan. Geophys. Res. Lett., 28, 17–20.
Kamachi, M., T. Kuragano, H. Ichikawa, H. Nakamura, A. Nishina, A. Isobe, D. Ambe, M. Arai, N. Gohda, S. Sugimoto, K. Yoshita, T. Sakurai and F. Uboldi (2004): Operational data assimilation system for the Kuroshio south of Japan: Reanalysis and validation. J. Oceanogr., 60, this issue, 303–312.
Kawabe, M. (1996): Model study of flow conditions causing the large meander of the Kuroshio south of Japan. J. Phys. Oceanogr., 26, 2449–2461.
Kawabe, M. (2001): Interannual variations of sea level at the Nansei Islands and volume transport of the Kuroshio due to wind changes. J. Oceanogr., 57, 189–206.
Leben, R. R., G. H. Born and B. R. Engebreth (2002): Operational Altimeter Data Processing for Mesoscale Monitoring. Marine Geodesy, 25, 3–18.
Lee, T. N., W. E. Johns, R. J. Zantopp and E. R. Fillenbaum (1996): Moored observations of western boundary current variability and thermohaline circulation at 26.5?N in the Subtropical North Atlantic. J. Phys. Oceanogr., 26, 962–983.
Lee, T. N., W. E. Johns, C. T. Liu, D. Zhang, R. Zantopp and Y. Yang (2001): Mean transport and seasonal cycle of the Kuroshio east of Taiwan with comparison to the Florida Current. J. Geophys. Res., 106, 22143–22158.
Lie, H.-J., C.-H. Cho, J.-H. Lee, P. Niiler and J.-H. Hu (1998): Separation of the Kuroshio water and its penetration onto the continental shelf west of Kyushu. J. Geophys. Res., 103, 2963–2976.
Nakano, T., T. Kuragano and Y. Liu (1998): Variations of oceanic conditions east of the Ryukyu Islands. p. 129–140. In Proceedings of Japan and China Joint Symposium on Cooperative Study of Subtropical Circulation System, 1-4 December 1997, Nagasaki, Japan, Seikai National Fisheries Research Institute, Nagasaki.
Nitani, H. (1972): Beginning of the Kuroshio. p. 129–163. In Kuroshio, Its Physical Aspects, ed. by H. Stommel and K. Yoshida, University of Tokyo Press, Tokyo.
Sekine, Y. and K. Kutsuwada (1994): Seasonal variation in volume transport of the Kuroshio south of Japan. J. Phys. Oceanogr., 24, 261–272.
Uchida, H. and S. Imawaki (2003): Eulerian mean surface velocity field derived by combing drifter and satellite altimeter data. Geophys. Res. Lett, 30, 1229, doi:10.1029/ 2002GL016445.
Yi, Y. (1995): Determination of gridded mean sea surface from altimeter data of TOPEX, ERS-1 and GEOSAT. Ph.D. Thesis, The Ohio Sate University, 140 pp.
Zhu, X.-H., I.-S. Han, J.-H. Park, H. Ichikawa, K. Murakami, A. Kaneko and A. Ostrovskii (2003): The Northeastward Current southeast of Okinawa Island observed during November 2000 to August 2001. Geophys. Res. Lett., 30, 1071, doi:10.1029/2002GL015867.
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Ichikawa, H., Nakamura, H., Nishina, A. et al. Variability of Northeastward Current Southeast of Northern Ryukyu Islands. Journal of Oceanography 60, 351–363 (2004). https://doi.org/10.1023/B:JOCE.0000038341.27622.73
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DOI: https://doi.org/10.1023/B:JOCE.0000038341.27622.73