Jets and large-scale vortices in rotating Rayleigh-Bénard convection

Abstract

One of the most prominent dynamical features of turbulent, rapidly-rotating convection is the formation of large-scale coherent structures, driven by Reynolds stresses resulting from the small-scale convective flows. In spherical geometry, such structures consist of intense zonal flows that are invariant along the rotation axis. In planar geometry, long-lived, depth-invariant structures also form at large scales, but, in the absence of horizontal anisotropy, they consist of vortices that grow to the domain size. In this work, through the introduction of horizontal anisotropy into a numerical model of planar rotating convection by the adoption of unequal horizontal box sizes (i.e. $L_x\le L_y$, where the $xy$-plane is horizontal), we investigate whether unidirectional flows and large-scale vortices can coexist. We find that only a small degree of anisotropy is required to bring about a transition from dynamics dominated by persistent large-scale vortices to dynamics dominated by persistent unidirectional flows parallel to the shortest horizontal direction. When the anisotropy is sufficiently large, the unidirectional flow consists of multiple jets, generated on a timescale smaller than a global viscous timescale, thus signifying that the upscale energy transfer does not spontaneously feed the largest available mode in the system. That said, the multiple jets merge on much longer timescales. Large-scale vortices of size comparable with $L_x$ systematically form in the flanks of the jets and can be persistent or intermittent. This indicates that large-scale vortices, either coexisting with jets or not, are a robust dynamical feature of planar rotating convection.

arXiv commentsubmitted to Physical Review Fluids

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• Magnetic and rotational quenching of the $\Lambda$ effect
• Energy cascades in rapidly rotating and stratified turbulence within elongated domains
• Fingering convection in the stably-stratified layers of planetary cores
• Shape and size of large-scale vortices: A generic fluid pattern in geophysical fluid dynamics
• Bridging the Rossby number gap in rapidly rotating thermal convection
• Direct driving of simulated planetary jets by upscale energy transfer
• Convective dynamics with mixed temperature boundary conditions: why thermal relaxation matters and how to accelerate it
• Out-of-equilibrium fluxes shape the self-organization of locally-interacting turbulence