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Article Dans Une Revue Physical Review Letters Année : 2020

Shortcut to Geostrophy in Wave-Driven Rotating Turbulence: The Quartetic Instability

Résumé

We report on laboratory experiments of wave-driven rotating turbulence. A set of wave makers produces inertial-wave beams that interact nonlinearly in the central region of a water tank mounted on a rotating platform. The forcing thus injects energy into inertial waves only. For moderate forcing amplitude, part of the energy of the forced inertial waves is transferred to subharmonic waves, through a standard triadic resonance instability. This first step is broadly in line with the theory of weak turbulence. Surprisingly however, stronger forcing does not lead to an inertial-wave turbulence regime. Instead, most of the kinetic energy condenses into a vertically invariant geostrophic flow, even though the latter is unforced. We show that resonant quartets of inertial waves can trigger an instability --the "quartetic instability"-- that leads to such spontaneous emergence of geostrophy. In the present experiment, this instability sets in as a secondary instability of the classical triadic instability.
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Dates et versions

hal-02518160 , version 1 (25-03-2020)

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Maxime Brunet, Basile Gallet, Pierre-Philippe Cortet. Shortcut to Geostrophy in Wave-Driven Rotating Turbulence: The Quartetic Instability. Physical Review Letters, 2020, 124, pp.124501. ⟨10.1103/PhysRevLett.124.124501⟩. ⟨hal-02518160⟩
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