2023 Fiscal Year Research-status Report
On the internal waves and turbulent mixing generated by the flow-topography interaction in the Kuroshio region
| Project/Area Number |
23KF0056
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| Research Institution | Ehime University |
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Principal Investigator |
郭 新宇 愛媛大学, 沿岸環境科学研究センター, 教授 (10322273)
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| Co-Investigator(Kenkyū-buntansha) |
WANG SHUYA 愛媛大学, 沿岸環境科学研究センター, 外国人特別研究員
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| Project Period (FY) |
2023-04-25 – 2025-03-31
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| Keywords | トカラ海峡 / 黒潮 / 内部潮汐 / 乱流混合 / 内部波 |
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| Outline of Annual Research Achievements |
By conducting numerical simulations and analyzing reanalysis data from OGCM, we explore internal waves in the Tokara Strait where the Kuroshio and complex bottom topographies coexist. We reveal that semidiurnal internal tides make a major contribution to energy dissipation there. We also investigated the interannual variation of semidiurnal internal tidal energy conversion and found that it is mainly influenced by the forcing barotropic tides rather than by the Kuroshio. Semidiurnal internal tides disintegrate via parametric subharmonic instability (PSI) which generates high-wavenumber near-inertial waves, therefore enhancing mixing. Although the Kuroshio suppresses PSI along its paths, energy dissipation induced by PSI is much higher than that caused only by the Kuroshio itself (Wang et al., submitted to JGR: Oceans). For comparison, we also investigate the internal tides in a shelf sea south of Japan. The internal tides generation there is affected by both stratification and Kuroshio variations. As internal tides radiate away from their generation sites, they are refracted by the Kuroshio due to spatially varying stratification and background currents (Wang et al., 2023, Progress in Oceanography).
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
This project went smoothly during the first fiscal year due to the following reasons. First, the PD and host professor work closely to achieve the goal of this project. We have regular discussions and group meetings to share and interpret the results together. Second, our laboratory is equipped with high-performance computers and workstations, enabling the numerical simulation and data analyses as planned. Third, we have established collaborations with other researchers from institutes in Japan (e.g., JAMSTEC, Kagoshima University, and Kyushu University). These researchers generously share with us their observational data and model outputs, which accelerates our progress. They also provide insightful comments and suggestions for this project. Last but not least, we also join academic meetings frequently to present our results and communicate with other researchers, and the feedback from them indeed improves this project.
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| Strategy for Future Research Activity |
In addition to internal tides, the Kuroshio-topography interaction also generates submesoscale processes including vortices and internal lee waves, which are also capable of driving mixing. By analyzing the data from high-resolution (~1 km) OGCM and performing additional simulations, we will explore the characteristics and statistical features of these submesoscale processes and their relation to the Kuroshio. Especially, we will focus on the energy cascade from the Kuroshio to eddies/waves as well as the energy budget. Furthermore, we are going to reveal the interaction between eddies and internal waves and indicate the role of wave-current interaction in energy dissipation. To achieve these goals, we have obtained high-resolution model outputs via collaborating with researchers from JAMSTEC. We will also configure our model with a much higher resolution to get insight into the dissipation of eddies and waves. By combining modeling results and theoretical interpretation, we intend to identify the dominant process driving turbulent mixing in the study region.
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| Causes of Carryover |
投稿中の論文の出版費として25万円の予算を用意したが。査読と改訂に時間が掛かり、年度内の出版ができなかったため、次年度に使用することにした。
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