Seasonal variations of the surface currents in the Tsushima Strait |
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| Authors: | Yutaka Yoshikawa Akira Masuda Kenichi Marubayashi Michiyoshi Ishibashi |
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| Institution: | (1) National Fisheries University, 2-7-1 Nagata-Honmachi, Shimonoseki 759-6595, Japan;(2) National Research Institute of Fisheries Science, Fisheries Research Agency, 2-12-4 Fukuura, Kanazawa Yokohama, 236-8648, Japan;(3) Research Institute for Applied Mechanics, Kyushu University, 6-1 Kasuga-kouen, Kasuga Fukuoka, 816-8580, Japan;(4) Hydrospheric Atmospheric Research Center, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan;(5) Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8564, Japan;(6) Department of Mechanical and Environmental Informatics, Graduate School of Information Science and Engineering, Tokyo Institute of Technology, 2-12-1, O-okayama, Meguro-ku Tokyo, 152-8552, Japan |
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| Abstract: | Seasonal variations of the surface currents in the Tsushima Strait were investigated by analyzing the monthly mean surface
currents measured with HF radar. Several new features of the surface currents have been found. One notable feature is the
large, complicated seasonal variation in the current structure in the eastern channel of the strait. For example, in the southeastern
and northwestern regions of the channel, southwestward countercurrents are found in summer while southeastward acrossshore
currents are found in autumn and winter. The wind-driven flow (Ekman flow) as well as surface geostrophic currents are responsible
for these complicated variations of the surface currents. To quantify each variation of the flow and current, the wind-driven
flow was calculated from the monthly wind (more precisely, the friction velocity) using the monthly speed factor and deflection
angle estimated in our previous study, and the surface geostrophic currents were then estimated by subtracting the wind-driven
flow from the measured surface currents. It was found that the acrossshore currents are the wind-driven flow, and that the
surface geostrophic currents flow almost in the along-shore direction, indicating the validity of the decomposition of the
surface velocity into the wind-driven flow and the geostrophic currents using the speed factor and deflection angle. A real-vector
empirical orthogonal function (EOF) analysis of the surface geostrophic currents shows a pair of eddies in the lee of Tsushima
and Iki Islands as the first mode, which indicates that the southwestward countercurrents in the eastern channel are formed
primarily by the incoming Tsushima Warm Current. |
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