Rotating convective turbulence in Earth and planetary cores

Aurnou, J. M.; Calkins, Michael A.; Cheng, Jonathan; Julien, Keith; King, E. M.; Nieves, David; Soderlund, K. M.; Stellmach, Stephan

doi:10.1016/j.pepi.2015.07.001

Cited by 133 publications

(155 citation statements)

References 122 publications

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“…DNS investigations [60] and laboratory experiments [1,14] show excellent agreement with the simulations of the QG convection equations. In particular, Stellmach et al [60] showed that it is necessary to reach very small Ekman numbers (Ek 10 −7 ) and Rossby numbers (Ro 0.05) to reach the asymptotic regime in which the dipolar structure of the inversecascade-generated vortex is preferred over the cyclonic vortices that become predominant in the broken-symmetry regime present at higher Ekman and Rossby numbers [24,27,53,66].…”

Section: Introductionsupporting

confidence: 58%

“…Investigations in spherical geometries are of obvious importance for planets, but must employ lower efficiency numerics typically and are therefore more restricted in parameter space [1]. The DNS investigation of Stellmach and Hansen [59] confirmed the predictions of Soward [55] that a strong, time-oscillatory mean magnetic field can be generated near the onset of convection.…”

Section: Introductionmentioning

confidence: 70%

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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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Section: Introductionsupporting

confidence: 58%

Section: Introductionmentioning

confidence: 70%

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

et al. 2016

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“…Similarly, such structures are approximately four orders of magnitude below the limits of planetary magnetic field observations. Thus, individual Λ o = 0 onset-scale convection columns, should they exist in Earth's core, are then not relevant to our interpretation of geomagnetic flux patches or their temporal variations [24,51,52].…”

Section: A Foray Into Linear Theorymentioning

confidence: 98%

The cross-over to magnetostrophic convection in planetary dynamo systems

Aurnou

King²

2017

Proc. R. Soc. A.

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A contribution to the special feature 'Perspectives in astrophysical and geophysical fluids' . is the system scale magnetic Reynolds number and D is the length scale of the system. On scales well above L X , magnetostrophic convection dynamics should not be possible. Only on scales smaller than L X should it be possible for the convective behaviours to follow the predictions for the magnetostrophic branch of convection. Because L X is significantly smaller than the system scale in most dynamo models, their large-scale flows should be quasi-geostrophic, as is confirmed in many dynamo simulations. Estimating Λ o 1 and Rm o 10 3 in Earth's core, the cross-over scale is approximately 1/1000 that of the system scale, suggesting that magnetostrophic convection dynamics exists in the core only on small scales below those that can be characterized by geomagnetic observations.

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“…They present numerical simulations (of rotating, Boussinesq convection in Cartesian domains) that bolster this view. Aurnou et al (2015) summarize a variety of theoretical and laboratory work on the related topic of rapidly rotating convection in Earth and planetary cores; see also King et al (2012), Stellmach et al (2014), and Cheng et al (2015) for analysis of the flow morphology and heat transport in various regimes. Separately, Julien et al (2012) have conducted simulations of asymptotically reduced equations applicable to the rapidly rotating Rayleigh-Bénard problem, and find that while heat transport in the weakly-rotating limit is essentially set by the properties of the boundary layers, transport in the rapidly rotating regime is set by properties in the bulk.…”

Section: Basics Of Convection and Rotationmentioning

confidence: 99%

Magnetism, dynamo action and the solar-stellar connection

Brun

Browning

2017

Living Rev Sol Phys

239

182

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The Sun and other stars are magnetic: magnetism pervades their interiors and affects their evolution in a variety of ways. In the Sun, both the fields themselves and their influence on other phenomena can be uncovered in exquisite detail, but these observations sample only a moment in a single star's life. By turning to observations of other stars, and to theory and simulation, we may infer other aspects of the magnetism-e.g., its dependence on stellar age, mass, or rotation rate-that would be invisible from close study of the Sun alone. Here, we review observations and theory of magnetism in the Sun and other stars, with a partial focus on the "Solar-stellar connection": i.e., ways in which studies of other stars have influenced our understanding of the Sun and vice versa. We briefly review techniques by which magnetic fields can be measured (or their presence otherwise inferred) in stars, and then highlight some key observational findings uncovered by such measurements, focusing (in many cases) on those that offer particularly direct constraints on theories of how the fields are built and maintained. We turn then to a discussion of how the fields arise in different objects: first, we summarize some essential elements of convection and dynamo theory, including a very brief discussion of mean-field theory and related concepts. Next we turn to simulations of convection and magnetism in stellar interiors, highlighting both some peculiarities of field generation in different types of stars and some unifying physical processes that likely influence dynamo action in general. We conclude with a brief

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Rotating convective turbulence in Earth and planetary cores

Cited by 133 publications

References 122 publications

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

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

The cross-over to magnetostrophic convection in planetary dynamo systems

Magnetism, dynamo action and the solar-stellar connection

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