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Accueil > Actualités > Séminaires > Séminaires 2023

Mardi 25 Avril 11h00 - LEGI Salle K118

Benjamin Favier, IRPHE

Zonal jets and vortex clusters in laboratory experiments

We use an experimental approach to address the questions of zonal jets and vortex clusters formation typical of planetary flows. A strong topographic β-effect is obtained inside a water-filled rotating tank thanks to the paraboloidal fluid free upper surface. A small-scale turbulent forcing is performed by circulating water through the base of the tank. Time-resolving particle image velocimetry reveals the self-organization of the flow into multiple zonal jets with a 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 modelling based on the quasi-geostrophic approximation reveals that this bifurcation results from the resonance between the directly forced Rossby waves and the background zonal flow. In a second experiment, cyclonic vortices are generated around the periphery of the container, which is an analogue of mid-latitudes, and their decaying dynamics is then studied. The transition from Rossby waves to localised vortices, their drift towards the pole and the eventual formation of vortex clusters will be briefly discussed.

Contact Nathanael Machicoane for more information or to schedule a discussion with the seminar speaker.