Structure and Variability of the Kuroshio Current in Tokara Strait

Ming Feng International Pacific Research Center, SOEST, University of Hawaii, Honolulu, Hawaii

Search for other papers by Ming Feng in
Current site
Google Scholar
PubMed
Close
,
Humio Mitsudera International Pacific Research Center, SOEST, University of Hawaii, Honolulu, Hawaii, and Frontier Research System for Global Change, Tokyo, Japan

Search for other papers by Humio Mitsudera in
Current site
Google Scholar
PubMed
Close
, and
Yasushi Yoshikawa Japan Marine Science and Technology Center, Yokosuka, Japan

Search for other papers by Yasushi Yoshikawa in
Current site
Google Scholar
PubMed
Close
Restricted access

Abstract

Four years of mooring array measurements in Tokara Strait, south of Kyushu, Japan, from 1992 to 1996 are used to analyze the structure and temporal variability of the Kuroshio Current. The mean Kuroshio current in Tokara Strait shows a nearly permanent subsurface double-core structure, possibly due to topographic blockage effects.

The dominant variations of the Kuroshio in Tokara Strait are separated into long-term variability (typically 100-day period) and short-term variability (10 days to 1 month) according to spectrum and wavelet analysis. The long-term variability has a large horizontal scale across the strait, with a striking twofold banded structure in spatial correlations. This is due to the north–south Kuroshio axis shift that advects the double-core structure of the mean current. The axis shift can be indexed with the northeastward current velocity at the northernmost station; a composite analysis using this index shows well-defined northward and southward axis shift structures of the Kuroshio current. From the composite of the TOPEX/Poseidon sea level anomaly in terms of this index, the Kuroshio axis shift and the current structure change are associated with a dipole-shape sea level anomaly east of Tokara Strait. On the other hand, the short-term variability of high kinetic energy only has a small horizontal scale within the northern part of the current, which is related to frontal variability.

There exists a deep southwestward undercurrent below 600 m in the northern part of Tokara Strait, flowing along the isobaths. The undercurrent becomes stronger during the northward shift of the Kuroshio axis, while it almost disappears during the southward shift.

+ Current affiliation: Division of Marine Research, CSIRO, Hobart, Tasmania, Australia.

Corresponding author address: Dr. Humio Mitsudera, IPRC/SOEST, University of Hawaii, Honolulu, HI 96822.

humiom&commatest.hawaii.edu

Abstract

Four years of mooring array measurements in Tokara Strait, south of Kyushu, Japan, from 1992 to 1996 are used to analyze the structure and temporal variability of the Kuroshio Current. The mean Kuroshio current in Tokara Strait shows a nearly permanent subsurface double-core structure, possibly due to topographic blockage effects.

The dominant variations of the Kuroshio in Tokara Strait are separated into long-term variability (typically 100-day period) and short-term variability (10 days to 1 month) according to spectrum and wavelet analysis. The long-term variability has a large horizontal scale across the strait, with a striking twofold banded structure in spatial correlations. This is due to the north–south Kuroshio axis shift that advects the double-core structure of the mean current. The axis shift can be indexed with the northeastward current velocity at the northernmost station; a composite analysis using this index shows well-defined northward and southward axis shift structures of the Kuroshio current. From the composite of the TOPEX/Poseidon sea level anomaly in terms of this index, the Kuroshio axis shift and the current structure change are associated with a dipole-shape sea level anomaly east of Tokara Strait. On the other hand, the short-term variability of high kinetic energy only has a small horizontal scale within the northern part of the current, which is related to frontal variability.

There exists a deep southwestward undercurrent below 600 m in the northern part of Tokara Strait, flowing along the isobaths. The undercurrent becomes stronger during the northward shift of the Kuroshio axis, while it almost disappears during the southward shift.

+ Current affiliation: Division of Marine Research, CSIRO, Hobart, Tasmania, Australia.

Corresponding author address: Dr. Humio Mitsudera, IPRC/SOEST, University of Hawaii, Honolulu, HI 96822.

humiom&commatest.hawaii.edu

Save
  • Adamec, D., 1998: Modulation of the seasonal signal of the Kuroshio extension during 1994 from satellite data. J. Geophys. Res.,103, 10209–10222.

  • Akiyama, H., Y. Ohno, and S. Saitoh, 1992: Kuroshio warm filament passing around the Tokara Strait (in Japanese with English abstract). Umi to Sora,68, 99–112.

  • AVISO/Altimetry, 1996: AVISO (Archive, Validation and Interpretation of Satellite Oceanographic data) user handbook for sea level anomaly altimeter products. Edition 2.0. AVI-NT-011-312-CN, 26 pp. [Available from CLS, Space Oceanography Division, 8–10, rue Hermès, 31526 Ramonville Saint-Agne, France.].

  • Bingham, F. M., and L. D. Talley, 1991: Estimates of Kuroshio transport using an inverse technique. Deep-Sea Res.,38, S21–S43.

  • Chao, S.-Y., 1984: Bimodality of the Kuroshio. J. Phys. Oceanogr.,14, 92–103.

  • Esbensen, S. K., and Y. Kushnir, 1981: The heat budget of the global ocean: An atlas based on estimates from surface marine observations. Climate Research Institute, Oregon State University Tech. Rep. 29, 27 pp. [Available from Oregon State University, Corvallis, OR 97331.].

  • Fraedrich, K., C. Ziehmann, and F. Sielmann, 1995: Estimates of spatial degrees of freedom. J. Climate,8, 361–369.

  • Fukasawa, M., and T. Teramoto, 1986: Characteristics of deep currents off Cape Shiono-mosadi before and after formation of the large meader of the Kuroshio in 1981. J. Oceanogr. Soc. Japan,42, 53–68.

  • Hanawa, K., and H. Mitsudera, 1985. On daily average of oceanographic data. Coastal Oceanogr. Bull.,23, 79–87.

  • Hurlburt, H., A. Wallcraft, W. Schmitz, P. Hogan, and E. Metzger, 1996: Dynamics of the Kuroshio/Oyashio current system using eddy-resolving models of the North Pacific Ocean. J. Geophys. Res.,101, 941–976.

  • James, C., M. Wimbush, and H. Ichikawa, 1999: Kuroshio meanders in the East China Sea. J. Phys. Oceanogr.,29, 259–272.

  • Josey, S. A., E. C. Kent, D. Oakley, and P. K. Taylor, 1996: A new global air–sea heat and momentum flux climatology. Int. WOCE Newslett.,24, 3–5.

  • Kawabe, M., 1980: Sea level variations around the Nansei Islands and the large meander in the Kuroshio south of central Japan. J. Oceanogr. Soc. Japan,36, 227–235.

  • ——, 1988: Variability of Kuroshio velocity assessed from the sea-level difference between Naze and Nishinoomote. J. Oceanogr. Soc. Japan,44, 293–304.

  • ——, 1995: Variations of current path, velocity, and volume transport of the Kuroshio in relation with the large meander. J. Phys. Oceanogr.,25, 3103–3117.

  • Kutsuwada, K., and Y. Morikawa, 1996: Interannual variability of the Kuroshio path/transport south of Japan using coastal sea-level. Tokai University Rep.,41, 171–183.

  • Lau, K.-M., and H. Weng, 1995: Climate signal detection using wavelet transform: How to make a time series sing. Bull. Amer. Meteor. Soc.,76, 2391–2402.

  • Masuda, A., 1982: An interpretation of the bimodal character of the stable Kuroshio path. Deep-Sea Res.,29, 471–484.

  • Mitsudera, H., Y. Yoshikawa, B. Taguchi, and H. Nakamura, 1997: High-resolution Kuroshio/Oyashio System model: Preliminary results (in Japanese with English abstract). Japan Marine Science and Technology Center Rep. 36, 19 pp. [Available from Japan Marine Science and Technology Center, Yokosuk 237-0061, Japan.].

  • Nagata, Y., and K. Takeshita, 1985: Variation of the sea surface temperature distribution across the Kuroshio in the Tokara Strait. J. Oceanogr. Soc. Japan,41, 244–258.

  • Nakano, T., I. Kaneko, and Y. Takatsuki, 1994: The Kuroshio structure estimated by the inverse method. J. Phys. Oceanogr.,24, 609– 618.

  • Nitani, H., 1972: Beginning of the Kuroshio. Kuroshio, Physical Aspects of the Japan Current. H. Stommel and K. Yoshida, Eds., University of Washington Press, 129–164.

  • Oberhuber, J. M., 1988: An atlas based on the COADS Data Set. Max Planck Institute for Meteorology Tech Rep. 15. [Available from Max-Planck-Institut für Meteorologie, Bundesstr. 55, D-20146 Hamburg, Germany.].

  • Qiu, B., 1999: Seasonal eddy field modulation of the North Pacific subtropical countercurrent: TOPEX/Poseidon observations and theory. J. Phys. Oceanogr.,29, 2471–2486.

  • ——, and W. Miao, 2000: Kuroshio path variations south of Japan: Bimodality as a self-sustained internal oscillation. J. Phys. Oceanogr.,30, 2124–2137.

  • ——, T. Toda, and N. Imasato, 1990: On Kuroshio fluctuations in the East China Sea using satellite and in situ observational data. J. Geophys. Res.,95, 18191–18204.

  • Rikiishi, K., and K. Sasaki, 1988: Geostrophic balance of the Kuroshio as inferred from surface current and sea level observations. J. Oceanogr. Soc. Japan,44, 305–314.

  • Sachs, L., 1978: Applied Statistics: A Handbook of Techniques. Springer-Verlag, 706 pp.

  • Stammer, D., 1997: Steric and wind-induced changes in TOPEX/POSEIDON large-scale sea surface topography observations. J. Geophys. Res.,102, 20987–21009.

  • Takematsu, M., K. Kawatate, W. Koterayama, T. Suhara, and H. Mitsuyasu, 1986: Moored instrument observations in the Kuroshio south of Kyushu. J. Oceanogr. Soc. Japan,42, 201–211.

  • Uchida, H., S. Imawaki, and J. Hu, 1998: Comparison of Kuroshio surface velocities derived from satellite altimeter and drifting buoy data. J. Oceanogr.,54, 115–122.

  • Wimbush, M., H. Ichikawa, J. Book, H. Uchida, and H. Kinoshita, 1998: Separating baroclinic and barotropic sea-surface height components in the ASUKA region, by combining altimeter and inverted echo sounder measurements. Proc. Symp. on Ocean– Earth Dynamics and Satellite Altimetry, S. Imawaki, Ed., 33– 50.

  • Yamagata, T., and S. Umatani, 1989: Geometry-forced coherent structures as a model of the Kuroshio large meander. J. Phys. Oceanogr.,19, 130–138.

  • Yamamoto, H., K. Ando, and A. Misumi, 1993: Estimation of Kuroshio volume transport in the East China Sea—Based on Kuroshio cruise in Oct. 1989, in Oct. 1990 and in Oct. 1991 (in Japanese with English abstract). Japan Marine Science and Technology Center Rep. 30, 37–59. [Available from Japan Marine Science and Technology Center, Yokosuk 237-0061, Japan.].

  • ——, and Coauthors, 1998: Variability of Kuroshio current in the Tokara Strait (in Japanese with English abstract). Japan Marine Science and Technology Center Rep. 37, 45 pp. [Available from Japan Marine Science and Technology Center, Yokosuk 237-0061, Japan.].

  • Yasuda, I., J. Yoon, and N. Suginohara, 1985: Dynamics of the Kuroshio large meander: Barotropical model. J. Oceanogr. Soc. Japan,41, 259–273.

All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 923 246 89
PDF Downloads 541 135 23