Internal Waves Generated by Tidal Flows over a Triangular Ridge with Critical Slopes

  • Yuhua Nie
  • Zhiwu ChenEmail author
  • Jieshuo Xie
  • Jiexin Xu
  • Yinghui He
  • Shuqun Cai


Direct numerical simulations are performed to investigate the generation of internal waves by tide-topography interaction in a lab-scale model. The bottom topography is a triangular ridge with two critical slopes. With increasing tidal forcing, subharmonic instabilities are identified, which cause internal wave beams to become unstable and turbulent. Kinetic energy densities in the upward going beams from the ridge top are stronger than those from the ridge bottom, whereas the reverse is true for the energy flux. This disparity between energy and energy flux is due to the existence of strong pressure disturbances near the ridge bottom. On each side of the critical ridge, there exists an amphidromic point, from which internal wave beams are emitted in opposite directions. The calculated energy conversion rate scales linearly with the square of the forcing amplitude and agrees within 13% of theoretical prediction, even when turbulence occurs. The fraction of radiated baroclinic energy becomes saturated in the range of low excursion parameter considered, which agrees with the behavior in large-scale systems wherein mixing parameterizations must be used. The present work enriches the studies on the generation of internal waves over a critical triangular ridge.

key words

Internal wave beam parametric subharmonic instability internal wave energetics tide-topography interaction 


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This work was jointly supported by the Key Research Program of Frontier Sciences, Chinese Academy of Sciences (CAS) (No. QYZDJ-SSW- DQC034), the National Natural Science Foundation of China (Nos. 41430964, 41521005, 41776007, and 41506005), the Pearl River S&T Nova Program of Guangzhou (No. 201610010012), the Youth Innovation Promotion Association CAS (No. 2018378), and No. ISEE2018PY05 from CAS.


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Copyright information

© Science Press, Ocean University of China and Springer-Verlag GmbH Germany, part of Springer Nature 2019

Authors and Affiliations

  • Yuhua Nie
    • 1
  • Zhiwu Chen
    • 2
    Email author
  • Jieshuo Xie
    • 2
  • Jiexin Xu
    • 2
  • Yinghui He
    • 2
  • Shuqun Cai
    • 2
    • 3
    • 4
  1. 1.South China Sea Information Center of State Oceanic AdministrationGuangzhouChina
  2. 2.State Key Laboratory of Tropical Oceanography, South China Sea Institute of OceanologyChinese Academy of SciencesGuangzhouChina
  3. 3.University of Chinese Academy of SciencesBeijingChina
  4. 4.Institution of South China Sea Ecology and Environmental EngineeringChinese Academy of SciencesGuangzhouChina

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