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Experimental study of superharmonic internal wave resonant triads in finite-depth nonuniform stratifications

Dheeraj Varma1,*, Corentin Pacary1, Thierry Dauxois1, and Sylvain Joubaud1,2

  • *Contact author: nldvrm@gmail.com
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Phys. Rev. Fluids 9, 094806 – Published 30 September, 2024

DOI: https://doi.org/10.1103/PhysRevFluids.9.094806

Abstract

We present an experimental study on the excitation of superharmonic internal wave by resonant interaction of internal wave modes in finite-depth nonuniform stratifications. In a nonuniform stratification, the primary wave field composed of a single horizontally propagating vertical mode or combination of two horizontally propagating vertical modes is forced from one end of the tank using the wave generator at a forcing frequency ω0. The spontaneous excitation of a superharmonic wave at frequency 2ω0 by resonant interaction of the internal wave modes of the primary wave field forced at frequency ω0 is observed. We experimentally demonstrate that even an isolated single mode could resonantly interact with itself to excite a superharmonic wave at frequency 2ω0 in a nonuniform stratification, which is inhibited in the case of a uniform stratification. The resonant peak frequencies at which the strength of superharmonic signal is maximum, and the corresponding vertical structure of the superharmonic internal wave mode, qualitatively agree well with the theoretical predictions obtained from the weakly nonlinear analysis. The paper concludes with a discussion on experiments performed to observe superharmonic triadic resonant interactions in an oceanlike nonuniform stratification profile, for which the excited superharmonic internal wave modes were found to be trapped within the pycnocline region.

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Phys. Rev. Fluids 9, 094806– Published 30 September, 2024
  • Received 7 January 2023
  • Accepted 30 August 2024
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