Multistability and rare spontaneous transitions between climate and jet configurations in a barotropic model of the Jovian mid-latitude troposphere
Abstract
We demonstrate that turbulent zonal jets, analogous to Jupiter 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 phenomena 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. In order 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, with an exponentially small probability as the Ekman dissipation decreases (Arrhenius law). This phe-nomenology is controlled by two different types of instantons in the limit of vanishing noise. Moreover, we are able to compute the saddles of the corresponding effective dynamics. We also investigate the detailed dynamics of solutions having three alternating jets. We uncover an unexpectedly rich dynamics governed by the symmetric group S3 of permutations, with two distinct families of instantons, which is a surprise for a system where everything seemed stationary in the hundreds of simulations of this model performed in the past.
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