Regimes of thermo-compositional convection and related dynamos in rotating spherical shells

Abstract

Convection and magnetic field generation in the Earth and planetary interiors are driven by both thermal and compositional gradients. In this work numerical simulations of finite-amplitude double-diffusive convection and dynamo action in rapidly rotating spherical shells full of incompressible two-component electrically-conducting fluid are reported. Four distinct regimes of rotating double-diffusive convection identified in a recent linear analysis (Silva et al., 2019, Geophys. Astrophys. Fluid Dyn., doi:10.1080/03091929.2019.1640875) are found to persist significantly beyond the onset of instability while their regime transitions remain abrupt. In the semi-convecting and the fingering regimes characteristic flow velocities are small compared to those in the thermally- and compositionally-dominated overturning regimes, while zonal flows remain weak in all regimes apart from the thermally-dominated one. Compositionally-dominated overturning convection exhibits significantly narrower azimuthal structures compared to all other regimes while differential rotation becomes the dominant flow component in the thermally-dominated case as driving is increased. Dynamo action occurs in all regimes apart from the regime of fingering convection. While dynamos persist in the semi-convective regime they are very much impaired by small flow intensities and very weak differential rotation in this regime which makes poloidal to toroidal field conversion problematic. The dynamos in the thermally-dominated regime include oscillating dipolar, quadrupolar and multipolar cases similar to the ones known from earlier parameter studies. Dynamos in the compositionally-dominated regime exhibit subdued temporal variation and remain predominantly dipolar due to weak zonal flow in this regime. These results significantly enhance our understanding of the primary drivers of planetary core flows and magnetic fields.

Accepted to Geophys. Astrophys. Fluid Dyn. on 2020-04-24; Submitted to Geophys. Astrophys. Fluid Dyn. on 2019-07-16

References in corpus (7)

• Chemical Transport and Spontaneous Layer Formation in Fingering Convection in Astrophysics
• Prandtl number dependence of convection driven dynamos in rotating spherical fluid shells
• Formation, stratification, and mixing of the cores of Earth and Venus
• Parameter dependences of convection driven dynamos in rotating spherical fluid shells
• Patterns of convection in rotating spherical shells
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Cited by in corpus (8)

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• Heat transport and convective velocities in compositionally-driven convection in neutron star and white dwarf interiors
• Fingering convection in the stably-stratified layers of planetary cores
• Effects of shell thickness on cross-helicity generation in convection-driven spherical dynamos
• Transition to chaos and magnetic field generation in rotating Rayleigh-Bénard convection
• Regime transitions of dynamos driven by fingering double-diffusive convection
• Influence of Rotation on Fingering Convection in Planetary Cores
• Differential rotation in convecting spherical shells with non-uniform viscosity and entropy diffusivity