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Impacts of subtidal motions and the earth rotation on modal characteristics of the semidiurnal internal tide

Abstract

Subtidal motions, such as large-scale circulations and mesoscale eddies, frequently occupy on the propagation path of internal waves in the ocean. Through solving a modified Taylor–Goldstein equation with subtidal currents, density stratification, and the earth rotation, this study investigates the impacts of subtidal motions and the earth rotation on the modal characteristics of the semidiurnal internal tide (SIT) based on long-term mooring measurements in the northern South China Sea (SCS). It is shown that the modal characteristics of the SIT are significantly influenced by the time-varying subtidal current and density stratification associated with energetic subtidal motions in the northern SCS. The earth rotation plays a minor role in modulating the modal characteristics of the SIT in the northern SCS, but it becomes effective at middle and high latitudes when strong subtidal current shear associated with subtidal motions is present. Moreover, the strong subtidal current associated with subtidal motions may significantly affect the critical latitude of the SIT. The observational results reported here will help to improve our understanding of the modal characteristics of internal tides under the influence of subtidal motions in global oceans.

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Acknowledgements

This work was supported by National Key Research and Development Program of China (2016YFC1402605), National Natural Science Foundation of China (Grants 41506011, 41676011, and 41706005), Qingdao National Laboratory for Marine Science and Technology (Grant 2015ASKJ01), Key Research and Development Program of Shandong (Grant 2016CYJS02A03), Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant 41521091), NSFC-Shandong Joint Fund for Marine Science Research Centers (Grant U1406402), and Global Change and AirSea Interaction Project (Grant nos. GASI-03-01-01-03, GASI-IPOVAI-01-03, and GASI-IPOVAI-01-02). The altimeter product was produced by SSALTO/DUCAS and distributed by AVISO, with support from CNES (available online at http://www.aviso.oceanobs.com/duacs). The HYCOM product is downloaded from the website at http://hycom.org/. The processed mooring data used in the work will be available from Ocean and Atmosphere Data Center, Ocean University of China, at http://coadc.ouc.edu.cn/index.php/Index/dataset/id/38?l=en-us?l=zh-cn, and now are available from the authors upon request as data collection is ongoing.

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Correspondence to Xiaodong Huang.

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Cite this article

Wang, Z., Huang, X., Yang, Y. et al. Impacts of subtidal motions and the earth rotation on modal characteristics of the semidiurnal internal tide. J Oceanogr 76, 15–27 (2020). https://doi.org/10.1007/s10872-019-00524-7

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Keywords

  • Internal tide
  • Modal characteristic
  • Subtidal motion
  • Rotation