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Near-inertial parametric subharmonic instability of internal wave beams in a background mean flow

Published online by Cambridge University Press:  01 February 2021

Boyu Fan Open the ORCID record for Boyu Fan [Opens in a new window]  and
T.R. Akylas
Boyu Fan
Affiliation:
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA02139, USA
T.R. Akylas*
Affiliation:
Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA02139, USA
*
†Email address for correspondence: [email protected]
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Abstract

The effect of a small background constant horizontal mean flow on the parametric subharmonic instability (PSI) of locally confined internal wave beams is discussed for the case where the beam frequency is close to twice the inertial frequency due to background rotation. Under this condition, PSI is particularly potent because of the vanishing of the group velocity at the inertial frequency, which prolongs contact of near-inertial subharmonic perturbations with the primary wave. The mean flow generally stabilizes the very short-scale limit of such perturbations. By contrast, the stability of longer-scale perturbations hinges on the strength and the direction of the mean flow; particularly, a negative mean flow (antiparallel to the horizontal projection of the beam group velocity) can extend the sub-inertial range of PSI. However, a large enough mean flow of either sign ultimately weakens PSI.

JFM classification

Geophysical and Geological Flows: Internal waves
Type
JFM Rapids
Information
Journal of Fluid Mechanics , Volume 911 , 25 March 2021 , R3
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Copyright
© The Author(s), 2021. Published by Cambridge University Press

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References

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