Journal of Oceanography, Vol. 57 (No. 2), pp. 141-154, 2001
Yoshiaki Toba1,2*, Junichi Kimura2,3, Hiroshi Murakami1, Myoungsun Kim2,4, Yasushi Yoshikawa2 and Koji Shimada2
1Earth Observation Research Center, National Space Development Agency of Japan, 1-9-9 Roppongi, Minato-ku, Tokyo 106-0032, Japan
2Japan Marine Science and Technology Center, 2-15 Natsushima-cho, Yokosuka 237-0061, Japan
3METOCEAN ENVIRONMENT INC., 2-2-2 Hayabuchi, Tsuzuki-ku, Yokohama 224-0025, Japan
4Telecommunications Advancement Organization of Japan, 2-31-19 Shiba, Minato-ku, Tokyo 105-0014, Japan
(Received 8 March 2000; in revised form 12 October 2000; accepted 12 October 2000)
Abstract: In the previous paper (Toba and Murakami, 1998) we reported on an unusual path of the Kuroshio Current System, which occurred in April 1997 (April 1997 event), using the Ocean Color and Temperature Scanner (OCTS) data of the Advanced Earth Observing Satellite (ADEOS). The April 1997 event was characterized by the flow of the Kuroshio along the western slope (northward) and the eastern slope (southward) of the Izu-Ogasawara Ridge, a very southerly turning point at about 32°N, followed by a straight northward path up to 37°N of the Kuroshio Extension along the eastern flank of the Izu-Ogasawara and the Japan Trenches. Overlaying of depth contours on ADEOS-OCTS chlorophyll-a images at the April 1997 event demonstrates the bottom topography effects on the current paths. A new finding based on TOPEX/Poseidon altimeter data is that the sea-surface gradient across the Kuroshio/Kuroshio Extension diminished greatly in the sea area southeast of the central Japan, as a very temporary phenomenon prior to this event. This temporary diminishing of the upper-ocean current velocity might have caused a stronger bottom effect along the Izu-Ogasawara Ridge, and over the Izu-Ogasawara Trench disclosed a weak background, barotropic trench-flank current pattern, which existed otherwise independently of the Kuroshio Extension. The very southerly path of the Kuroshio Extension from winter 1996 to autumn 1998 corresponded, with a time lag of about 1.5 years, to the previous La Niña tendency with weaker North Equatorial Current. The April 1997 event occurred in accordance with its extreme condition.