Effects of anisotropies in turbulent magnetic diffusion in mean-field solar dynamo models

Journal Article · Thu Apr 10 04:00:00 EDT 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/785/1/49· OSTI ID:22357161

Pipin, V. V. ^[1]; Kosovichev, A. G. ^[2]

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1. Institute of Solar-Terrestrial Physics, Russian Academy of Sciences, Irkutsk 664033 (Russian Federation)
2. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305 (United States)

We study how anisotropies of turbulent diffusion affect the evolution of large-scale magnetic fields and the dynamo process on the Sun. The effect of anisotropy is calculated in a mean-field magnetohydrodynamics framework assuming that triple correlations provide relaxation to the turbulent electromotive force (so-called the 'minimal τ-approximation'). We examine two types of mean-field dynamo models: the well-known benchmark flux-transport model and a distributed-dynamo model with a subsurface rotational shear layer. For both models, we investigate effects of the double- and triple-cell meridional circulation, recently suggested by helioseismology and numerical simulations. To characterize the anisotropy effects, we introduce a parameter of anisotropy as a ratio of the radial and horizontal intensities of turbulent mixing. It is found that the anisotropy affects the distribution of magnetic fields inside the convection zone. The concentration of the magnetic flux near the bottom and top boundaries of the convection zone is greater when the anisotropy is stronger. It is shown that the critical dynamo number and the dynamo period approach to constant values for large values of the anisotropy parameter. The anisotropy reduces the overlap of toroidal magnetic fields generated in subsequent dynamo cycles, in the time-latitude 'butterfly' diagram. If we assume that sunspots are formed in the vicinity of the subsurface shear layer, then the distributed dynamo model with the anisotropic diffusivity satisfies the observational constraints from helioseismology and is consistent with the value of effective turbulent diffusion estimated from the dynamics of surface magnetic fields.

• OSTI ID: 22357161
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 785; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABUNDANCE
ANISOTROPY
BENCHMARKS
COMPUTERIZED SIMULATION
CONVECTION
CORRELATIONS
DIFFUSION
DISTRIBUTION
ELECTROMOTIVE FORCE
EVOLUTION
LIMITING VALUES
MAGNETIC FIELDS
MAGNETIC FLUX
MAGNETOHYDRODYNAMICS
MEAN-FIELD THEORY
RELAXATION
SUN
SUNSPOTS
TRANSPORT THEORY