The problem of small and large scale fields in the solar dynamo

Abstract

Three closely related stumbling blocks of solar mean field dynamo theory are discussed: how dominant are the small scale fields, how is the alpha effect quenched, and whether magnetic and current helicity fluxes alleviate the quenching? It is shown that even at the largest currently available resolution there is no clear evidence of power law scaling of the magnetic and kinetic energy spectra in turbulence. However, using subgrid scale modeling, some indications of asymptotic equipartition can be found. The frequently used first order smoothing approach to calculate the alpha effect and other transport coefficients is contrasted with the superior minimal tau approximation. The possibility of catastrophic alpha quenching is discussed as a result of magnetic helicity conservation. Magnetic and current helicity fluxes are shown to alleviate catastrophic quenching in the presence of shear. Evidence for strong large scale dynamo action, even in the absence of helicity in the forcing, is presented.

to appear in Astron. Nachr., in honour of the retirement of Michael Stix

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Cited by in corpus (10)

• Astrophysical magnetic fields and nonlinear dynamo theory
• The case for a distributed solar dynamo shaped by near-surface shear
• Magnetic fluctuations and formation of large-scale inhomogeneous magnetic structures in a turbulent convection
• Shear-current effect in a turbulent convection with a large-scale shear
• Cyclical period changes in HT Cas: a clear difference between systems above and below the period gap
• Realistic modeling of local dynamo processes on the Sun
• Mean-field dynamo in a turbulence with shear and kinetic helicity fluctuations
• Nonlinear shear-current dynamo and magnetic helicity transport in sheared turbulence
• Discussion of the Electromotive Force Terms in the Model of Parker-unstable Galactic Disks with Cosmic Rays and Shear
• Magnetic flux in the inter-network quiet Sun from comparison with numerical simulations