Detecting fluctuations of the Kuroshio axis south of Japan using TOPEX/POSEIDON altimeter data |
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| Authors: | Shiro Imawaki Mayumi Gotoh Hiroyuki Yoritaka Noriya Yoshioka Atsunobu Misumi |
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| Institution: | (1) Research Institute for Applied Mechanics, Kyushu University, 816 Kasuga, Fukuoka, Japan;(2) Department of Earth System Science and Technology, Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 816 Kasuga, Fukuoka, Japan;(3) Hydrographic Department, Maritime Safety Agency, 5-3-1 Tsukiji, Chuo-ku, 104 Tokyo, Japan;(4) Kobe Marine Observatory, Japan Meteorological Agency, Nakayamate, Chuo-ku, 650 Kobe, Japan;(5) Present address: Japan Marine Science and Technology Center, Natsushima, 237 Yokosuka, Kanagawa, Japan;(6) Present address: PASCO Environmental Science Institute, 2-32-1 Yoga, Setagaya-ku, 158 Tokyo, Japan |
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| Abstract: | Sea surface dynamic topography (SSDT) can be divided into temporal mean SSDT and fluctuation SSDT. The former is approximated with a climatological mean SSDT and the latter is derived from satellite altimetry data, to give an approximated total SSDT (called a composite SSDT). The method is applied to detecting fluctuations of the Kuroshio axis south of Japan using TOPEX/POSEIDON altimeter data from the first year mission in 1992–1993. The fluctuation SSDT averaged over a wide area south of Japan clearly shows an annual cycle with an amplitude of about 15 cm. Temporal changes of SSDT along a subsatellite track crossing the Kuroshio compare moderately well with those estimated from repeated hydrographic observations, although there is a discrepancy of unknown origin. The composite SSDT also compares well with SSDT estimated from the same hydrographic data. Horizontal distribution of the surface geostrophic velocity component normal to subsatellite tracks is derived every ten days from the composite SSDT. Most locations of estimated strong eastward geostrophic velocities coincide well with locations of the Kuroshio axis determined every 15 days fromin situ surface velocity measurements on various vessels; for example, a fairly large meander of the Kuroshio south of Honshu is clearly detected. It is concluded that the composite SSDT can be used reliably to detect fluctuations of the Kuroshio axis south of Japan. |
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