TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 59 (No. 3), pp. 291-301, 2003

Geostrophy in the Intermediate and Deep Layers of the Kuroshio and Its Recirculation Regions South of Japan

Motohiko Kashima1*, Shiro Imawaki2, Shin-ichiro Umatani2, Hiroshi Uchida3, Yuji Hashibe4, Hiroshi Ichikawa5 and Masao Fukasawa3

1Japan Science and Technology Corporation, Honcho, Kawaguchi, Saitama 332-0012, Japan
2Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
3Japan Marine Science and Technology Center, Natsushima, Yokosuka, Kanagawa 237-0061, Japan
4Space Engineering Development Co. Ltd., Nakano, Nakano-ku, Tokyo 164-0001, Japan
5Faculty of Fisheries, Kagoshima University, Kagoshima 890-0056, Japan

(Received 9 September 2002; in revised form 15 October 2002; accepted 24 October 2002)

Abstract: Theoretically, the geostrophic approximation holds for the low-frequency flow field, but no detailed examination has been done on how well the estimated geostrophic velocity corresponds with the observed velocity. Intensive surveys were carried out during 1993-1995 in the Kuroshio and its recirculation regions south of Shikoku, Japan, including repeated hydrographic surveys and direct current measurements at nominal depths of 700, 1500 and 3000 m. For these depth intervals, vertical differences of estimated geostrophic velocity are compared with those of observed velocity. For the intermediate layer (between 700 and 1500 m depths), the slope of the regression line is 0.99, correlation coefficient is 0.98, and the root-mean-square of difference from geostrophic balance is 2.8 cm/s which is close to the estimated error of 2.1 cm/s. For the deep layer (between 1500 and 3000 m depths), the corresponding values are 0.82, 0.93, 1.2 cm/s and 2.0 cm/s, respectively. The results indicate that the estimated geostrophic velocity compares well with the observed velocity in these regions.

*Corresponding author E-mail: kashima@riam.kyushu-u.ac.jp

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