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研究キーワードinternal tides・Tokara Strait・Kuroshio・turbulent mixing・shelf sea oceanography・parametric subharmonic instability・heat budget・bottom Ekman layer

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• Shuya Wang, Xinyu Guo, Akihiko Morimoto, Anzhou Cao, Eisuke Tsutsumi, Yasumasa Miyazawa, Sergey M. Varlamov . Semidiurnal Internal Tides in a Shelf Sea South of Japan: Characteristics,2024 · 記述言語： 英語 掲載種別： 研究論文（学術雑誌） Tidal mixing in a shelf sea south of Japan (Bungo Channel) plays an important role in modulating the water exchange between the Seto Inland Sea and Pacific Ocean. In this study, based on moored observations and model results from the Japan Coastal Ocean Predictability Experiment—Tides (JCOPE-T), the generation, propagation, and dissipation of semidiurnal internal tides in the Bungo Channel are investigated. Observational results indicate that semidiurnal internal tides induce strong baroclinic currents reaching 0.3 m/s. Their energy shows obvious spring-neap tidal cycles, generally coinciding with the local barotropic tidal forcing. By conducting the empirical orthogonal function analysis, we find that the observed semidiurnal internal tides are mainly dominated by the first two baroclinic modes. The JCOPE-T results suggest two main generation sites for semidiurnal internal tides in the region: one is located at a narrow strait north of the Bungo Channel, while the other is at the shelf break south of the Bungo Channel. The latter makes a major contribution to the observed semidiurnal internal tides. Northward internal tides generated at the shelf break are superposed with those generated at the narrow strait, causing a complex interference pattern in the channel. The temporal variation of semidiurnal internal tides in the Bungo Channel is affected by several factors. The intraseasonal variation of semidiurnal internal tides can be modulated by the Kuroshio warm water intrusion (Kyucho) because the occurrence of Kyucho changes the stratification in the channel and hence affects the energy conversion. The seasonal variation of semidiurnal internal tides in the Bungo Channel is determined mainly by the seasonally varying stratification; while those generated at the shelf break are under the combined influence of seasonal stratification and background currents. Southward internal tides from the shelf break are refracted due to the spatially varying stratification and background currents. The varying Kuroshio path and strength modulate the refraction of internal tides. DOI： 10.1016/j.pocean.2024.103229 Scopus
• S. Itoh, E. Tsutsumi, E. Masunaga, T. T. Sakamoto, K. Ishikawa, D. Yanagimoto, Y. Hoshiba, H. Kaneko, D. Hasegawa, K. Tanaka, H. Fukuda, T. Nagata . Seasonal cycle of the confluence of the Tsu2022 · 掲載種別： 研究論文（学術雑誌） 出版者・発行元： American Geophysical Union (AGU) DOI： 10.1029/2022JC018556 その他リンク： https://onlinelibrary.wiley.com/doi/full-xml/10.1029/2022JC018556
• Shuya Wang, Xinyu Guo, Anzhou Cao, Eisuke Tsutsumi, Xu Chen . Parametric Subharmonic Instability of the M2 Internal Tides in the Tokara Strait . Journal of Geo2022 · 掲載種別： 研究論文（学術雑誌） The Tokara Strait is a mixing hotspot due to the coexistence of complex bottom topographies and strong composite flow including both the Kuroshio and tidal currents. Although previous studies have revealed several mechanisms from the view of Kuroshio-Topography interaction, the role of tides in driving mixing is still not clear. Given that it is located at the M2 critical latitude (29°N), parametric subharmonic instability (PSI) is expected as an important process responsible for the mixing. Here, we study PSI of the M2 internal tides in the Tokara Strait based on a high-resolution model. Our model results indicate that intense near-inertial waves are generated via PSI, which exhibit a horizontally layered structure and have much larger vertical wavenumbers than the M2 internal tides. Energy is transferred from the M2 internal tides to the near-inertial waves around the generation sites, and most of the near-inertial energy is dissipated locally. The dissipation rates of near-inertial waves are comparable to those of the M2 internal tides. Simulations with and without the Kuroshio Current revealed the suppression of PSI along the Kuroshio path, which could be attributed to two mechanisms. First, the Kuroshio Current modifies the local minimum internal wave frequency by its horizontal and vertical shear, making the condition for PSI not satisfied. Second, the Kuroshio Current advects the near-inertial waves downstream in the Okinawa Trough, which inhibits the accumulation of near-inertial energy there. However, in most of the areas outside the Kuroshio path, PSI majorly contributes to mixing in and around the Tokara Strait. DOI： 10.1029/2022JC019622 Scopus
• Takahiro Endoh, Eisuke Tsutsumi, Chang-Su Hong, Gyu-Nam Baek, Ming-Huei Chang, Yiing Jang Yang, Takeshi Matsuno, Jae Hak Lee . Estimating propagation speed and direction, and vertical d2021 · 掲載種別： 研究論文（学術雑誌） 出版者・発行元： Elsevier BV DOI： 10.1016/j.csr.2021.104644

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