Abstract
An analysis of a 68-year monthly hindcast output from an eddy-resolving ocean general circulation model reveals the relationship between the interannual variability of the Kerama Gap transport (KGT) and the Kuroshio/Ryukyu Current system. The study found a significant difference in the interannual variability of the upstream and downstream transports of the East China Sea- (ECS-) Kuroshio and the Ryukyu Current. The interannual variability of the KGT was found to be of paramount importance in causing the differences between the upstream and downstream ECS-Kuroshio. Additionally, it contributed approximately 37% to the variability of the Ryukyu Current. The interannual variability of the KGT was well described by a two-layer rotating hydraulic theory. It was dominated by its subsurface-intensified flow core, and the upper layer transport made a weaker negative contribution to the total KGT. The subsurface flow core was found to be mainly driven by the subsurface pressure head across the Kerama Gap, and the pressure head was further dominated by the subsurface density anomalies on the Pacific side. These density anomalies could be traced back to the eastern open ocean, and their propagation speed was estimated to be about 7.4 km/d, which is consistent with the speed of the local first-order baroclinic Rossby wave. When the negative (positive) density anomaly signal reached the southern region of the Kerama Gap, it triggered the increase (decrease) of the KGT towards the Pacific side and the formation of an anticyclonic (cyclonic) vortex by baroclinic adjustment. Meanwhile, there is an increase (decrease) in the upstream transport of the entire Kuroshio/Ryukyu Current system and an offshore flow that decreases (increases) the downstream Ryukyu Current.
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Acknowledgements
All data and tools underlying this analysis are openly available: Japan Agency for Marine-Earth Science and Technology (JAMSTEC) Ocean General Circulation Model for the Earth Simulator (OFES) dataset (https://www.jamstec.go.jp/ofes/). AVISO satellite altimeter data is available from https://www.aviso.altimetry.fr/en/home.html. The WOA data is downloaded from Asia-Pacific Data-Research Center (APDRC) (http://apdrc.soest.hawaii.edu/).
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Foundation item: The Fundamental Research Funds for the Central Universities under contract No. B220201024.
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Zhou, H., Yu, K., Qin, J. et al. Study on the interannual variability of the Kerama Gap transport and its relation to the Kuroshio/Ryukyu Current system. Acta Oceanol. Sin. 43, 1–14 (2024). https://doi.org/10.1007/s13131-023-2281-8
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DOI: https://doi.org/10.1007/s13131-023-2281-8