Zonal jets at the laboratory scale: hysteresis and Rossby waves resonance

TL;DR

This study experimentally investigates the formation, stability, and long-term evolution of zonal jets in planetary flows, revealing a subcritical bifurcation driven by Rossby wave resonance and turbulence in a laboratory setting.

Contribution

It introduces an experimental setup with a topographic beta-effect and turbulent forcing to explore jet dynamics, highlighting the resonance mechanism behind jet bifurcation.

Findings

Identification of two jet regimes: steady and energetic dynamic jets.

Discovery of a subcritical bifurcation influenced by Rossby wave resonance.

Experimental evidence of flow self-organization into multiple jets.

Abstract

The dynamics, structure and stability of zonal jets in planetary flows are still poorly understood, especially in terms of coupling with the small-scale turbulent flow. Here, we use an experimental approach to address the questions of zonal jets formation and long-term evolution. A strong and uniform topographic $\beta$-effect is obtained inside a water-filled rotating tank thanks to the paraboloidal fluid free upper surface combined with a specifically designed bottom plate. A small-scale turbulent forcing is performed by circulating water through the base of the tank. Time-resolving PIV measurements reveal the self-organization of the flow into multiple zonal jets with strong instantaneous signature. We identify a subcritical bifurcation between two regimes of jets depending on the forcing intensity. In the first regime, the jets are steady, weak in amplitude, and directly forced by the local Reynolds stresses due to our forcing. In the second one, we observe highly energetic and dynamic jets of width larger than the forcing scale. An analytical modeling based on the quasi-geostrophic approximation reveals that this subcritical bifurcation results from the resonance between the directly forced Rossby waves and the background zonal flow.