Advances in mean-field dynamo theory and applications to astrophysical turbulence

Abstract

Recent advances in mean-field theory are reviewed and applications to the Sun, late-type stars, accretion disks, galaxies, and the early Universe are discussed. We focus particularly on aspects of spatio-temporal nonlocality, which is one of the main insights that emerged from applying the test-field method to magnetic fields of different length and timescales. We also review the status of nonlinear quenching and the relation to magnetic helicity, which is an important observational diagnostic of modern solar dynamo theory. Both solar and some stellar dynamos seem to operate in an intermediate regime that has not yet been possible to model successfully. This regime is bracketed by antisolar-like differential rotation on one end and stellar activity cycles belonging to the superactive stars on the other. The difficulty in modeling this regime may be related to shortcomings in modelling solar/stellar convection. On galactic and extragalactic length scales, the observational constraints are still less stringent and uncertain, but recent advances both in theory and in observations suggest that more conclusive comparisons may soon be possible. The possibility of inversely cascading magnetic helicity throughout all of the early Universe is particularly exciting in explaining the lower limits of magnetic fields on cosmological length scales and the possibility of parity breaking and finite helicity of such a field.

65 pages, 11 figures, J. Plasma Phys, accepted

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Cited by in corpus (54)

• Dynamo theories
• The Turbulent Dynamo
• Physical Processes in Star Formation
• Modeling of Magneto-Rotational Stellar Evolution I. Method and first applications
• Galactic Dynamos
• Magnetic field amplification in accretion discs around the first stars: implications for the primordial IMF
• Chiral magnetohydrodynamic turbulence in core-collapse supernovae
• Gravitoturbulent dynamos in astrophysical discs
• Solar large-scale magnetic field and cycle patterns in solar dynamo
• The primordial magnetic field in our cosmic backyard
• Turbulent processes and mean-field dynamo
• Rotation periods for cool stars in the open cluster Ruprecht 147 (NGC 6774): Implications for gyrochronology
• Alignment of the magnetic field in star forming regions and why it might be difficult to observe
• Magnetic field generation from primordial black hole distributions
• Magnetic fields in the accretion disks for various inner boundary conditions
• Turbulent transport coefficients in galactic dynamo simulations using singular value decomposition
• Torsional Oscillations in Dynamo Models with Fluctuations and Potential for Helioseismic Predictions of the Solar Cycles
• Effects of Emerging Bipolar Magnetic Regions in Mean-field Dynamo Model of Solar Cycles 23 and 24
• Solar dynamo cycle variations with a rotational period
• Dynamo instabilities in plasmas with inhomogeneous chiral chemical potential
• Helicity in the Large-Scale Galactic Magnetic Field
• Non-locality of the Turbulent Electromotive Force
• Turbulent magneto-genesis in a collisionless plasma
• Lagrangian statistics of a shock-driven turbulent dynamo in decaying turbulence
• On effects of surface bipolar magnetic regions on the convection zone dynamo
• Cosmic ray diffusion in magnetic fields amplified by nonlinear turbulent dynamo
• On large-scale dynamos with stable stratification and the application to stellar radiative zones
• Active-Region Tilt Angles from White-Light Images and Magnetograms: The Role of Magnetic Tongues
• MRI turbulence in vertically stratified accretion discs at large magnetic Prandtl numbers
• Iterative removal of sources to model the turbulent electromotive force
• Axisymmetric dynamo action produced by differential rotation, with anisotropic electrical conductivity and anisotropic magnetic permeability
• Correcting the effect of magnetic tongues on the tilt angle of bipolar active regions
• Unified treatment of mean-field dynamo and angular-momentum transport in magnetorotational instability-driven turbulence
• The origin and effect of hemispheric helicity imbalance in solar dynamo
• On the linear and non linear evolution of the RMHD Kelvin Helmholtz instability in a magnetically polarized fluid
• Spatio-temporal non-localities in a solar-like mean-field dynamo
• Effects of shell thickness on cross-helicity generation in convection-driven spherical dynamos
• Two-Loop Turbulent Helical Magnetohydrodynamics: Large-Scale Dynamo and Energy Spectrum
• Exploring helical dynamos with machine learning
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• Transition to chaos and magnetic field generation in rotating Rayleigh-Bénard convection
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