Large Meander Path Research Articles

Interannual correlations between sea level difference at the south coast of Japan and wind stress over the north pacific

Relationships of the sea level differences between Naze and Nishinoomote and between Kushimoto and Uragami with wind stress over the North Pacific are examined for interannual variability. These sea level differences are considered to be indications of Kuroshio transport in Tokara Strait and Kuroshio path south of Enshu-nada, respectively. In the sea level difference between Kushimoto and Uragami, dominant variations are found to have periods of about seven years and 3–4 years. The variation of about 7-year period, which corresponds to that in the Kuroshio path between the large meander and non-large meander, is coherent with the variation of the wind stress curl in a region about 2,400 km east of the Kii Peninsula, where negative stress curl weakens about two years before the sea level difference drops (i.e. the large meander path in the Kuroshio generates). The variation of the 3–4 year period is coherent with that of the wind stress in a large area covering the eastern equatorial Pacific, which suggests that it links with global-scale atmospheric variations. Interannual variation in sea level difference between Naze and Nishinoomote is not coherent with that between Kushimoto and Uragami, which suggests that it is not related to the variation of the Kuroshio path south of Enshu-nada, but is coherent with that of the zonally-integrated Sverdrup transport in the latitudinal zone along 30°N. It is suggested that the interannual variation of the Kuroshio transport in Tokara Strait can be explained by the barotropic response to the wind stress.

Transition processes between the three typical paths of the Kuroshio

Transitions between the three typical paths of the Kuroshio south of Japan (the nearshore and offshore non-large-meander paths and the large-meander path) are described using sea level data at Miyake-jima and HachijO-jima in the Izu Islands and temperature data at a depth of 200 m observed from 1964 to 1975 and in 1980.

Sea level variations at the Izu Islands and typical stable paths of the Kuroshio

Differences in daily mean sea level between Kushimoto and Uragami and daily mean sea levels at Miyake-jima and HachijO-jima in the Izu Islands are examined during the 1964–1980 period, and characteristics of the typical paths of the Kuroshio corresponding to the dominant sea level states are described. Sea levels at the islands show three dominant states: high and low sea level states (45 % and 31 %) in the non-large-meander period (October 1963 –7 August 1975) and high sea level state (64 %) in the large-meander period (8 August 1975–15 March 1980). This indicates the existence of three typical paths of the Kuroshio, and the states correspond to the nearshore and offshore non-large-meander paths and the typical large-meander path, respectively. The first path is located near the coast throughout the whole southern area off Japan, the second path leaves the coast around the Izu Ridge and passes south of HachijO-jima, and the third path is located near the coast over the ridge after meandering far to the south of Enshu-nada. The positions of the three typical paths are almost the same in the farthest upstream and downstream regions south of Japan between 131‡E and 142‡E. The nearshore and offshore non-large-meander paths overlap between Kyushu and the Kii Peninsula, being invariably close to the coast, while the typical large-meander path south of Shikoku is located offshore and changes its position meridionally. At the mid-depth of 400 m the nearshore non-large-meander and typical large-meander paths pass the Izu Ridge through the deep channel between Miyake-jima and HachijO-jima, while the offshore non-large-meander path passes through the deep region south of HachijOjima. The path of the Kuroshio at mid-depth is well constrained by the bottom topography of the Izu Ridge.