Generation of magnetic fields by large-scale vortices in rotating convection

Guervilly, Céline; Hughes, David W.; Jones, C. A.

doi:10.1103/physreve.91.041001

Cited by 43 publications

(65 citation statements)

References 24 publications

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“…The friction coefficient f r , which, in the case of Ekman pumping, stands for the ratio L=h, is left here as a parameter to control the relative importance of the geostrophic modes in the saturated flow. We expect other mechanisms of specific dissipation (see, e.g., magnetic [15,43], quadratic, scale dependant) to lead to similar results. The simulations hereafter are carried out with f r ¼ 10 −2 and f r ¼ 1.…”

Section: -2mentioning

confidence: 53%

“…The same issue arises in twodimensional turbulence, where it is solved adding largescale friction [49]. Lastly, additional physics, such as imposing a background magnetic field [15,43], can also be responsible for precluding the emergence of large-scale geostrophic flows. The friction coefficient f r , which, in the case of Ekman pumping, stands for the ratio L=h, is left here as a parameter to control the relative importance of the geostrophic modes in the saturated flow.…”

Section: -2mentioning

confidence: 99%

“…The energy stored in the geostrophic modes is comparable to the energy in the rest of the flow. Similarly to what is observed in forced rotating turbulence [31,40] or rapidly rotating thermal convection [41][42][43], a nonlocal inverse cascade of the geostrophic modes takes place until, at t ≃ 120 rotations onwards, one single large-scale vortex, or condensate, remains [ Fig. 1(c)].…”

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confidence: 99%

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Inertial Wave Turbulence Driven by Elliptical Instability

et al. 2017

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The combination of elliptical deformation of streamlines and vorticity can lead to the destabilization of any rotating flow via the elliptical instability. Such a mechanism has been invoked as a possible source of turbulence in planetary cores subject to tidal deformations. The saturation of the elliptical instability has been shown to generate turbulence composed of nonlinearly interacting waves and strong columnar vortices with varying respective amplitudes, depending on the control parameters and geometry. In this Letter, we present a suite of numerical simulations to investigate the saturation and the transition from vortex-dominated to wave-dominated regimes. This is achieved by simulating the growth and saturation of the elliptical instability in an idealized triply periodic domain, adding a frictional damping to the geostrophic component only, to mimic its interaction with boundaries. We reproduce several experimental observations within one idealized local model and complement them by reaching more extreme flow parameters. In particular, a wave-dominated regime that exhibits many signatures of inertial wave turbulence is characterized for the first time. This regime is expected in planetary interiors.

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Section: -2mentioning

confidence: 53%

Section: -2mentioning

confidence: 99%

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confidence: 99%

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Inertial Wave Turbulence Driven by Elliptical Instability

et al. 2017

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“…Tilgner [63,64] found a transition from the mean field dynamo mechanism of Childress and Soward [15] to a dynamo of fluctuation-type. The recent work of Guervilly et al [28] examined the influence of the inverse cascade and associated large-scale vortex on the resulting dynamo; they found that for P m 1, the mean magnetic field is weak and the inverse cascade is less pronounced, in comparison to a case at P m = 0.2 where a significant inverse cascade and mean magnetic field are present. It should be noted that all of these investigations, despite the advantage of being in a computationally simple plane layer, are at parameters well away from those relevant to planetary interiors.…”

Section: Introductionmentioning

confidence: 99%

Convection-driven kinematic dynamos at low Rossby and magnetic Prandtl numbers

et al. 2016

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Most large-scale planetary magnetic fields are thought to be driven by low Rossby number convection of a low magnetic Prandtl number fluid. Here kinematic dynamo action is investigated with an asymptotic, rapidly rotating dynamo model for the plane layer geometry that is intrinsically low magnetic Prandtl number. The thermal Prandtl number and Rayleigh number are varied to illustrate fundamental changes in flow regime, ranging from laminar cellular convection to geostrophic turbulence in which an inverse energy cascade is present. A decrease in the efficiency of the convection to generate a dynamo, as determined by an increase in the critical magnetic Reynolds number, is observed as the buoyancy forcing is increased. This decreased efficiency may result from both the loss of correlations associated with the increasingly disordered states of flow that are generated, and boundary layer behavior that enhances magnetic diffusion locally. We find that the spatial characteristics of α, and thus the large-scale magnetic field, is dependent only weakly on changes in flow behavior. In contrast to the large-scale magnetic field, the behavior of the small-scale magnetic field is directly dependent on, and therefore shows significant variations with, the small-scale convective flow field. However, our results are limited to the linear, kinematic dynamo regime; future simulations that include the Lorentz force are therefore necessary to assess the robustness of these results.

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“…The flow may then act as a dynamo, as a consequence of which the strong small-scale magnetic field diminishes the coherence of the Reynolds stresses, and hence the driving for the large-scale vortices. Whether this signifies the demise of the large-scale vortices, or whether they can recover, depends critically on the value of Rm, which determines whether the small-scale field can be maintained (Guervilly et al 2015). Although the physics is more complicated than that considered in this paper, in that the magnetic field is selfgenerated rather than imposed, the main underlying idea is again that a strong small-scale field can inhibit turbulent transport.…”

Section: Discussionmentioning

confidence: 88%

The Decay of a Weak Large-Scale Magnetic Field in Two-Dimensional Turbulence

Kondić

Hughes

Tobias

2016

ApJ

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We investigate the decay of a large-scale magnetic field in the context of incompressible, two-dimensional magnetohydrodynamic turbulence. It is well established that a very weak mean field, of strength significantly below equipartition value, induces a small-scale field strong enough to inhibit the process of turbulent magnetic diffusion. In light of ever-increasing computer power, we revisit this problem to investigate fluids and magnetic Reynolds numbers that were previously inaccessible. Furthermore, by exploiting the relation between the turbulent diffusion of the magnetic potential and that of the magnetic field, we are able to calculate the turbulent magnetic diffusivity extremely accurately through the imposition of a uniform mean magnetic field. We confirm the strong dependence of the turbulent diffusivity on the product of the magnetic Reynolds number and the energy of the large-scale magnetic field. We compare our findings with various theoretical descriptions of this process.

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Generation of magnetic fields by large-scale vortices in rotating convection

Cited by 43 publications

References 24 publications

Inertial Wave Turbulence Driven by Elliptical Instability

Inertial Wave Turbulence Driven by Elliptical Instability

Convection-driven kinematic dynamos at low Rossby and magnetic Prandtl numbers

The Decay of a Weak Large-Scale Magnetic Field in Two-Dimensional Turbulence

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