TERRAPUB Journal of Oceanography

Journal of Oceanography, Vol. 64 (No. 6), pp. 937-950, 2008

Study of the Kuroshio/Ryukyu Current System Based on Satellite-Altimeter and in situ Measurements

Magdalena Andres1*, Jae-Hun Park1, Mark Wimbush1, Xiao-Hua Zhu2, Kyung-Il Chang3 and Hiroshi Ichikawa4

1Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882-1197, U.S.A.
2State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China
3Research Institute of Oceanography/School of Earth and Environmental Sciences, Seoul National University, Silim-dong Gwanak-gu, Seoul 151-742, Korea
4Institute of Observational Research for Global Change, Japan Agency for Marine-Earth Science and Technology, Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan

(Received 26 March 2008; in revised form 17 June 2008; accepted 24 June 2008)

Abstract: Data from satellite altimeters and from a 13-month deployment of in situ instruments are used to determine an empirical relationship between sea-level anomaly difference (ΔSLA) across the Kuroshio in the East China Sea (ECS-Kuroshio) and net transport near 28°N. Applying this relationship to the altimeter data, we obtain a 12-year time series of ECS-Kuroshio transport crossing the C-line (KT). The resulting mean transport is 18.7 ± 0.2 Sv with 1.8 Sv standard deviation. This KT is compared with a similarly-determined time series of net Ryukyu Current transport crossing the O-line near 26°N southeast of Okinawa (RT). Their mean sum (24 Sv) is less than the mean predicted Sverdrup transport. These KT and RT mean-flow estimates form a consistent pattern with historical estimates of other mean flows in the East China Sea/Philippine Basin region. While mean KT is larger than mean RT by a factor of 3.5, the amplitude of the KT annual cycle is only half that of RT. At the 95% confidence level the transports are coherent at periods of about 2 years and 100-200 days, with RT leading KT by about 60 days in each case. At the annual period, the transports are coherent at the 90% confidence level with KT leading RT by 4-5 months. While the bulk of the Kuroshio enters the ECS through the channel between Taiwan and Yonaguni-jima, analysis of satellite altimetry maps, together with the transport time series, indicates that the effect of mesoscale eddies is transmitted to the ECS via the Kerama Gap southwest of Okinawa. Once the effect of these eddies is felt by the ECS-Kuroshio at 28°N, it is advected rapidly to the Tokara Strait.

*Corresponding author E-mail: mandres@gso.uri.edu

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