Planetary Dynamos

Busse, Friedrich H.

doi:10.1016/b978-0-444-53802-4.00172-x

Cited by 9 publications

(4 citation statements)

References 95 publications

(79 reference statements)

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“…Convection in a rotating spherical fluid shell provides one of the fundamental models for understanding the large-scale motions and the magnetic fields observed in many geophysical, planetary and astrophysical systems, see (Jones 2011, Glatzmaier 2013, Busse and Simitev 2015. Thermal and compositional convection occur, for instance, in Earth's outer core which is composed mostly of iron and nickel, alloyed to lighter elements, supposedly silicon, sulphur and oxygen (Jeanloz 1990).…”

Section: Introductionmentioning

confidence: 99%

The onset of thermo-compositional convection in rotating spherical shells

Silva

Mather

Simitev

2019

Geophysical & Astrophysical Fluid Dynamics

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Double-diffusive convection driven by both thermal and compositional buoyancy in a rotating spherical shell can exhibit a rather large number of behaviours often distinct from that of the single diffusive system. In order to understand how the differences in thermal and compositional molecular diffusivities determine the dynamics of thermo-compositional convection we investigate numerically the linear onset of convective instability in a double-diffusive setup. We construct an alternative equivalent formulation of the non-dimensional equations where the linearised double-diffusive problem is described by an effective Rayleigh number, Ra, measuring the amplitude of the combined buoyancy driving, and a second parameter, α, measuring the mixing of the thermal and compositional contributions. This formulation is useful in that it allows for the analysis of several limiting cases and reveals dynamical similarities in the parameters space which are not obvious otherwise. We analyse the structure of the critical curves in this Ra−α space, explaining asymptotic behaviours in α, transitions between inertial and diffusive regimes, and transitions between large scale (fast drift) and small scale (slow drift) convection. We perform this analysis for a variety of diffusivities, rotation rates and shell aspect ratios showing where and when new modes of convection take place.

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Section: Introductionmentioning

confidence: 99%

The onset of thermo-compositional convection in rotating spherical shells

Silva

Mather

Simitev

2019

Geophysical & Astrophysical Fluid Dynamics

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“…It is also a key ingredient for their habitability. As such, it has been the subject of numerous studies since the seminal work of Larmor and Joseph (1919), and it remains today an active and challenging research domain for theoretical, experimental and numerical approaches (see, e.g., Busse & Simitev, 2015;Cardin & Olson, 2015;Christensen & Wicht, 2015;Roberts, 2015). One of the prevailing questions is the source of fluid motions.…”

Section: Introductionmentioning

confidence: 99%

Turbulent Kinematic Dynamos in Ellipsoids Driven by Mechanical Forcing

Reddy

Favier

Bars

2018

Geophysical Research Letters

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Dynamo action in planetary cores has been extensively studied in the context of convectively driven flows. We show in this letter that mechanical forcings, namely, tides, libration, and precession, are also able to kinematically sustain a magnetic field against ohmic diffusion. Previous attempts published in the literature focused on the laminar response or considered idealized spherical configurations. In contrast, we focus here on the developed turbulent regime and we self‐consistently solve the magnetohydrodynamic equations in an ellipsoidal container. Our results open new avenues of research in dynamo theory where both convection and mechanical forcing can play a role, independently or simultaneously.

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“…Paleomagnetism and astrophysical studies disclosed the present or past existence of a magnetic field in telluric planets and satellites in our solar system [Stevenson, 2003;Busse and Simitev, 2015;Connerney, 2015]. The core dynamo process that converts kinetic energy into magnetic energy by dynamic motions in the liquid core is the most plausible mechanism for generating a long-lived magnetic field in the rocky planets and satellites [Stevenson, 2003].…”

Section: Introductionmentioning

confidence: 99%

The influence of sulfur on the electrical resistivity of hcp iron: Implications for the core conductivity of Mars and Earth

Sugitani

Ohta

Hirose

et al. 2017

Geophysical Research Letters

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Cosmochemical and geochemical studies suggest sulfur (S) as a light alloying element in the iron‐rich cores of telluric planets, but there is no report of sulfur's alloying effect on the electrical and thermal transport properties of iron (Fe); a subject that is closely related to the dynamo action and thermal evolution of planetary cores. We measured the electrical resistivity of hexagonal‐closed‐packed (hcp) structured Fe alloy containing 3 wt. % silicon (Si) and 3 wt. % S up to 110 GPa at 300 K. Combined with the reported resistivities of hcp Fe and hcp Fe‐Si alloy, we determined the impurity resistivity of S in a hcp Fe matrix at high pressures. The obtained impurity resistivity of S is found to be smaller than that of Si. Therefore, S is a weaker influence on the conductivity of Fe alloy, even if S is a major light element in the planetary cores.

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Planetary Dynamos

Cited by 9 publications

References 95 publications

The onset of thermo-compositional convection in rotating spherical shells

The onset of thermo-compositional convection in rotating spherical shells

Turbulent Kinematic Dynamos in Ellipsoids Driven by Mechanical Forcing

The influence of sulfur on the electrical resistivity of hcp iron: Implications for the core conductivity of Mars and Earth

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