Observations of Kuroshio variability in the East China Sea

Magdalena Andres, Jae-Hun Park, and Mark Wimbush

Graduate School of Oceanography, University of Rhode Island

South Ferry Rd., Narragansett, Rhode Island 02882, U.S.A.

E-mail：mandres@gso.uri.edu

Kyung Il Chang

School of Earth and Environmental Sciences, Seoul National University

Silim-dong Gwanak-gu, Seoul 151-742, Korea

Hiroshi Ichikawa

Institute of Observational Research for Global Change, JAMSTEC

2-15 Natsushima-cho, Yokosuka-city, Kanagawa, 237-0061, Japan.

Time series lasting 23 months of absolute velocity cross-sections and absolute transport of the Kuroshio in the East China Sea (ECS) were obtained using 11 inverted echo sounders and 2 ADCPs deployed near the regularly sampled PN-line. There are two regions of negative (southwestward) flow: a deep countercurrent over the continental slope beneath the Kuroshio axis and a recirculation offshore which extends through the whole water column. The depth of maximum velocity is bimodally distributed with occurrence peaks at the surface and 210 dbar.

The net absolute transport of the Kuroshio in the ECS peaked at 29.5 Sv followed 38 days later by an extreme minimum of 4.0 Sv. The mean is 18.7 ± 0.5 Sv (standard deviation, σ = 4.0 Sv). The mean positive and negative portions of this net flow are 25.1 ± 0.7 Sv (σ = 4.6 Sv) and -6.4 ± 0.6 Sv, (σ = 2.4 Sv) respectively, with 83% of the negative transport in the recirculation. Magnitudes of the positive and recirculation transports are positively correlated (r = 0.50) with recirculation lagging about 4 days. Spectral peaks in transport are observed at 11, 15, and ~60 days. The 11-day peak is related to meanders in Kuroshio position. The 15-day peak likely results from similar-period fluctuations of the inflow into the ECS east of Taiwan. Cross wavelet analysis shows that, despite an overall correlation between Kuroshio position and positive transport, (r = 0.4 with no lag), these two signals are incoherent near 60 days.