Introduction
The Kuroshio, a western boundary current of the North Pacific subtropical gyre, is known as its unique feature of its path change south off Japan coast, those are large-meander path and non-large meander path. The path change has been thought relating to the speed and/or volume transport of the Kuroshio (Akitomo et al., 1991). Over the Izu Ridge, the Kuroshio has typical three paths, those are, a large meander path, a near coast non-large meander path, and an offshore non-large meander path (Kawabe, 1985). The Kuroshio exists northern to Miyake Island (34N) in the former two paths, and exists near the Hachijo Island (33N) in the case of offshore non-large meander path. The Kuroshio throw out open ocean after the Izu ridge.
The North Pacific Subtropical Mode Water (NPSTMW), counterpart of the 18 degree Water in North Atlantic, exists south of Kuroshio region. The NPSTMW formation area is east of Izu Ridge and south of the Kuroshio Extension (Hanawa, 1987). The Water is advected westward and then throws into the Shikoku basin. In the Kuroshio counter current region there often exists eddies, such as cyclonic and anti-cyclonic eddies, and then are advected westward into the Shikoku basin (Yoshikawa et al., 1999).
In order to monitor features of the Kuroshio and its recirculation over the izu-Ridge, Physical Oceanography Group of Tohoku University has conducted Tokyo-Ogasawara Line Experiment (TOLEX) using a ferry ‘Ogasawara Maru' (Ogasawara Kaiun Co.), shuttling between Tokyo (35N, 140E) and Chichijima Island (27N, 142E). In this paper we will show seasonal and interannual variation of the Kuroshio using TOLEX-ADCP data.
Other field experiments, ongoing and near future study in JAMSTEC, will be also shown. One is done at the eastern edge of the lzu Ridge, to observe passage and evolution of eddies. And the other is future study, at the Kuroshio Extension region.
The TOLEX and other experiments area are shown in Fig. 1.
Kuroshio variation over the lzu Ridge using TOLEX-ADCP data
1. TOLEX-ADCP monitoring
The TOLEX has some subprograms. XBT measurements, TOLEX-XBT, have been conducted since August 1988 in order to monitor the upper thermal structure along the ship course (Hanawa and Yoshikawa, 1993: Yoshikawa et al., 1996). Additional monitoring has begun since February 1991 using shipboard Acoustic Doppler Current Profiler (ADCP), the TOLEX-ADCP (Hanawa et al., 1996). In this paper we will show seasonal and interannual variation of the Kuroshio using TOLEX-ADCP data. The data processing procedures and the preliminary results was shown in Hanawa et al. (1996).
