Do dynamo-waves propagate along isorotation surfaces?

Kitchatinov, L. L.

doi:10.1051/0004-6361:20021156

Cited by 16 publications

(30 citation statements)

References 20 publications

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“…This could be expected from the analysis given by Kitchatinov (2002). In our calculations, parameter (a) controls the excess of the magnetic diffusivity in the horizontal direction relative to the vertical direction.…”

Section: Discussionsupporting

confidence: 53%

“…It transfers the energy of magnetic fields from large to small scales and determines the characteristic spatial scale of the excited dynamo modes (see Parker 1971 and the reviews of Brandenburg & Subramanian 2005;Charbonneau 2011). The magnitude of turbulent diffusion impacts the period of the dynamo cycle, and the anisotropy of turbulent diffusion affects latitudinal drift of the large-scale magnetic field during the activity cycle, socalled the "butterfly" diagram (e.g., Yoshimura 1975;Parker 1979;Rogachevskii & Kleeorin 2000;Kitchatinov 2002).…”

Section: Introductionmentioning

confidence: 99%

“…The calculations are performed using the so-called minimal τ approximation of the mean field magnetohydrodynamics (Blackman & Field 2002;Brandenburg & Subramanian 2005). Given the previous results of Parker (1971) and Kitchatinov (2002), we expect that the anisotropy resulting from additional horizontal diffusion of magnetic field can change the direction of the dynamo wave propagation and increase the horizontal scale of the mean magnetic field. We find that this effect also decreases the overlap between the butterfly wings of the time-latitude diagrams of the large-scale toroidal magnetic field evolution, which improves agreement of the dynamo model with observations.…”

Section: Introductionmentioning

confidence: 99%

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Effects of Anisotropies in Turbulent Magnetic Diffusion in Mean-Field Solar Dynamo Models

Пипин

Kosovichev

2014

ApJ

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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.

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Section: Discussionsupporting

confidence: 53%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effects of Anisotropies in Turbulent Magnetic Diffusion in Mean-Field Solar Dynamo Models

Пипин

Kosovichev

2014

ApJ

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“…(6)− (8) it is seen that for the case of energy equipartition, ε = 1, the small-scale dynamo makes significant contributions to different parts of the MEMF. Kitchatinov (2002Kitchatinov ( , 2004 has found that anisotropic diffusion may be in a large part responsible for the equatorial drift of the toroidal LSMF. This drift is actually an extra diffusion (of both the toroidal and poloidal parts of the mean field) along the rotation axis e. In Eq.…”

Section: The Solar αmentioning

confidence: 99%

“…(1) which are of odd order in e, that is, the terms with coefficients f 1 will be referred to as anisotropic diffusion. The second part of this term, proportional to f (a) 1 (ε+1), is known to describe an extra diffusion along e (Kitchatinov et al 1994;Kitchatinov 2002Kitchatinov , 2004.…”

Section: Introductionmentioning

confidence: 99%

Stellar dynamos with ${\Omega} \times J$ effect

Пипин

Seehafer

2008

A&A

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Context. The standard dynamo model for the solar and stellar magnetic fields is based on the αΩ mechanism, namely, an interplay between differential rotation (the Ω effect) and a mean electromotive force generated by helical turbulent convection flows (the α effect). There are, however, a number of problems with the α effect and αΩ dynamo models. Two of them are that, in the case of the Sun, the obtained cycle periods are too short and the magnetic activity is not sufficiently concentrated at low latitudes. Aims. We explore the role of turbulent induction effects that may appear in addition to the α effect. The additional effects result from the combined action of rotation and an inhomogeneity of the large-scale magnetic field. The best known of them is the Ω × J effect. We also include anisotropic diffusion and a new dynamo term that is of third order in the rotation vector Ω. Methods. We studied axisymmetric mean-field dynamo models containing differential rotation, the α effect, and the additional turbulent induction effects. The model calculations were carried out using the rotation profile of the Sun as obtained from helioseismic measurements and radial profiles of other quantities according to a standard model of the solar interior. In addition, we consider a dynamo model for a full sphere that is based solely on the joint induction effects of rotation and an inhomogeneity of the large-scale magnetic field, without differential rotation and the α effect (a δ 2 dynamo model). This kind of dynamo model may be relevant for fully convective stars. Results. With respect to the solar dynamo, the inclusion of the additional turbulent induction effects increases the period of the dynamo and brings the large-scale toroidal field closer to the equator, thus improving the agreement of the models with the observations. For the δ 2 dynamo working in a full sphere, we find dynamo modes that are steady if the effect of anisotropic diffusion is not included. The inclusion of anisotropic diffusion yields a magnetic field oscillating with a period close to the turbulent magnetic diffusion time.

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Turbulent dynamo near tachocline and reconstruction of azimuthal magnetic field in the solar convection zone

Krivodubskij¹

2005

Astron. Nachr.

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Abstract. In order to extend the abilities of the αΩ dynamo model to explain the observed regularities and anomalies of the solar magnetic activity, the negative buoyancy phenomenon and the magnetic quenching of the α effect were included in the model, as well as newest helioseismically determined inner rotation of the Sun were used. Magnetic buoyancy constrains the magnitude of toroidal field produced by the Ω effect near the bottom of the solar convection zone (SCZ). Therefore, we examined two "antibuoyancy" effects: i) macroscopic turbulent diamagnetism and ii) magnetic advection caused by vertical inhomogeneity of fluid density in the SCZ, which we call the ∇ρ effect. The Sun's rotation substantially modifies the ∇ρ effect. The reconstruction of the toroidal field was examined assuming the balance between mean-field magnetic buoyancy, turbulent diamagnetism and the rotationally modified ∇ρ effect. It is shown that at high latitudes antibuoyancy effects block the magnetic fields in the deep layers of the SCZ, and so the most likely these deep-rooted fields could not become apparent at the surface as sunspots. In the near-equatorial region, however, the upward ∇ρ effect can facilitate magnetic fields of about 3000 -4000 G to emerge through the surface at the sunspot belt. Allowance for the radial inhomogeneity of turbulent velocity in derivations of the helicity parameter resulted in a change of sign of the α effect from positive to negative in the northern hemisphere near the bottom of the SCZ. The change of sign is very important for direction of the Parker's dynamo-waves propagation and for parity of excited magnetic fields. The period of the dynamo-wave calculated with allowance for the magnetic quenching is about seven years, that agrees by order of magnitude with the observed mean duration of the sunspot cycles. Using the modern helioseismology data to define dynamo-parameters, we conclude that north-south asymmetry should exist in the meridional field. At low latitudes in deep layers of the SCZ, the αΩ dynamo excites most efficiency the dipolar mode of the meridional field. Meanwhile, in high-latitude regions a quadrupolar mode dominates in the meridional field. The obtained configuration of the net meridional field is likely to explain the magnetic anomaly of polar fields (the apparent magnetic "monopole") observed near the maxima of solar cycles.

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Do dynamo-waves propagate along isorotation surfaces?

Cited by 16 publications

References 20 publications

Effects of Anisotropies in Turbulent Magnetic Diffusion in Mean-Field Solar Dynamo Models

Effects of Anisotropies in Turbulent Magnetic Diffusion in Mean-Field Solar Dynamo Models

Stellar dynamos with ${\Omega} \times J$ effect

Turbulent dynamo near tachocline and reconstruction of azimuthal magnetic field in the solar convection zone

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