2020/09/30 by Eric Simonnet, Joran Rolland, Freddy Bouchet
Earth and Planetary Sciences · Engineering · Physics and Astronomy · #Attractor #Barotropic fluid #Dissipation #Dissipative system #Earth Systems and Cosmic Evolution #Fluid dynamics and aerodynamics studies #Forcing (mathematics) #Intermittency #Multistability #Rossby number #Tropical and Extratropical Cyclones Research #Turbulence #astro-ph.EP #physics.ao-ph #physics.flu-dyn
paper · pdf · doi:10.1175/jas-d-20-0279.1
published as Journal of the Atmospheric Science, volume 78, issue 6, pages 1889 - 1911 · Submitted to Journal of Atmospheric Science, 38 pages, 21 figures. Version 3 corresponds to the version accepted in the Journal of Atmospheric Science, metadata are changed
arxiv created 2021/03/31 · openalex publication_date 2021/04/05 · openalex created_date 2021/04/13 · arxiv updated 2021/06/07 · openalex updated_date 2026/08/05
Abstract We demonstrate that turbulent zonal jets, analogous to Jovian ones, which are quasi stationary, are actually metastable. After extremely long times, they randomly switch to new configurations with a different number of jets. The genericity of this phenomenon suggests that most quasi-stationary turbulent planetary atmospheres might have many climates and attractors for fixed values of the external forcing parameters. A key message is that this situation will usually not be detected by simply running the numerical models, because of the extremely long mean transition time to change from one climate to another. To study such phenomena, we need to use specific tools: rare-event algorithms and large-deviation theory. With these tools, we make a full statistical mechanics study of a classical barotropic beta-plane quasigeostrophic model. It exhibits robust bimodality with abrupt transitions. We show that new jets spontaneously nucleate from westward jets. The numerically computed mean transition time is consistent with an Arrhenius law showing an exponential decrease of the probability as the Ekman dissipation decreases. This phenomenology is controlled by rare noise-driven paths called instantons . Moreover, we compute the saddles of the corresponding effective dynamics. For the dynamics of states with three alternating jets, we uncover an unexpectedly rich dynamics governed by the symmetric group of permutations, with two distinct families of instantons, which is a surprise for a system where everything seemed stationary in the hundreds of previous simulations of this model. We discuss the future generalization of our approach to more realistic models.