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

Пипин, В. В.; Kosovichev, A. G.

doi:10.1088/0004-637x/785/1/49

Cited by 14 publications

(21 citation statements)

References 41 publications

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“…The flux transport dynamo with very complicated meridional flow patterns was investigated, and it was shown that if an equatorward flow in low latitudes at the bottom of the con-vective zone is present, the flux transport dynamo works even in the case of a meridional circulation with very complicated flow structures 47 . Similar works are seen for dynamos with double and multiple cells 48,49 , and dynamos in the global 3D simulations 50,51 .…”

Section: Introductionsupporting

confidence: 77%

A New Simple Dynamo Model for Stellar Activity Cycle

Yokoi

Schmitt

Пипин

et al. 2016

ApJ

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A new simple dynamo model for stellar activity cycle is proposed. By considering an inhomogeneous mean flow effect on turbulence, it is shown that turbulent cross helicity (velocity-magnetic-field correlation) should enter the expression of turbulent electromotive force as the coupling coefficient for the mean absolute vorticity. The inclusion of the cross-helicity effect makes the present model different from the current α-Ω-type models mainly in two points. First, in addition to the usual α (helicity effect) and β (turbulent magnetic diffusivity), we consider the γ coefficient (cross-helicity effect) as a key ingredient of the dynamo process. Second, unlike the α and β coefficients, which are often treated as an adjustable parameter in the current studies, the spatiotemporal evolution of γ coefficient should be solved simultaneously with the mean magnetic-field equations. The basic scenario for the stellar activity cycle in the present model is as follows: In the presence of turbulent cross helicity, the toroidal field is induced by the toroidal rotation in mediation by the turbulent cross helicity. Then, as usual models, the α or helicity effect generates the poloidal field from the toroidal one. This poloidal field, induced by the α effect, produces a turbulent cross helicity whose sign is opposite to the original one (negative production of cross helicity). The cross helicity with the opposite sign starts producing a reversed toroidal field. Eigenvalue analyses of the simplest possible present model give a butterfly diagram, which confirms the above scenario as well as the equator-ward migrations, the phase relationship between the cross helicity and magnetic fields, etc. These results suggest that the oscillation of the turbulent cross helicity is a key for the activity cycle. The reversal of the turbulent cross helicity is not the result of the magnetic-field reversal, but the cause of the latter. This new model is expected to open up the possibility of the mean-field or turbulence closure dynamo approaches.PACS numbers: 95.30. Qd, 96.60.Hv, 96.60.Q, 96.60.qd

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Section: Introductionsupporting

confidence: 77%

A New Simple Dynamo Model for Stellar Activity Cycle

Yokoi

Schmitt

Пипин

et al. 2016

ApJ

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“…The eddy diffusivity is an order of 10 10 cm/s and less near the bottom of the convection zone. The diffusivity profile is the same as in our previous paper Pipin and Kosovichev [67].…”

Section: Resultsmentioning

confidence: 98%

“…where, E = u × b is the mean electromotive force with u and b standing for the turbulent fluctuating velocity and magnetic field respectively. Similar to our recent paper (see, [67,62]), we employ the mean electromotive force in form: where symmetric tensor α ij models the generation of magnetic field by the α-effect; antisymmetric tensorγ ij controls the mean drift of the large-scale magnetic fields in turbulent medium, including the magnetic buoyancy; the tensor η ijk governs the turbulent diffusion. The reader can find further details about the E in the above cited papers.…”

Section: Dynamo Equationsmentioning

confidence: 99%

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Nonkinematic solar dynamo models with double-cell meridional circulation

Пипин

2018

Journal of Atmospheric and Solar-Terrestrial Physics

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Employing the standard solar interior model as input we construct a dynamically-consistent nonlinear dynamo model that takes into account the detailed description of the Λ-effect, turbulent pumping, magnetic helicity balance, and magnetic feedback on the differential rotation and meridional circulation. The background mean-field hydrodynamic model of the solar convection zone accounts the solar-like angular velocity profile and the double-cell meridional circulation. We investigate an impact of the nonlinear magnetic field generation effects on the long-term variability and properties of the magnetic cycle. The nonlinear dynamo solutions are studied in the wide interval of the α effect parameter from a slightly subcritical to supercritical values. It is found that the magnetic cycle period decreases with the increasing cycle's magnitude. The periodic long-term variations of the magnetic cycle are excited in case of the overcritical α effect. These variations result from the hemispheric magnetic helicity exchange. It depends on the magnetic diffusivity parameter and the magnetic helicity production rate. The large-scale magnetic activity modifies the distribution of the differential rotation and meridional circulation inside convection zone. It is found that the magnetic feedback on the global flow affects the properties of the long-term magnetic cycles. We confront our findings with solar and stellar magnetic activity observations.

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“…We employ the anisotropic diffusion tensor which is derived in P08 and in (Pipin & Kosovichev 2014):…”

Section: Angular Momentum Balancementioning

confidence: 99%

Non-linear regimes in mean-field full-sphere dynamo

Пипин¹

2016

Mon. Not. R. Astron. Soc.

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The mean-field dynamo model is employed to study the non-linear dynamo regimes in a fully convective star of mass 0.3M rotating with period of 10 days. For the intermediate value of the parameter of the turbulent magnetic Prandl number, P m T = 3 we found the oscillating dynamo regimes with period about 40Yr. The higher P m T results to longer dynamo periods. If the large-scale flows is fixed we find that the dynamo transits from axisymmetric to non-axisymmetric regimes for the overcritical parameter of the αeffect. The change of dynamo regime occurs because of the nonaxisymmetric non-linear α-effect. The situation persists in the fully non-linear dynamo models with regards of the magnetic feedback on the angular momentum balance and the heat transport in the star. It is found that the large-scale magnetic field quenches the latitudinal shear in the bulk of the star. However, the strong radial shear operates in the subsurface layer of the star. In the nonlinear case the profile of the angular velocity inside the star become close to the spherical surfaces. This supports the equator-ward migration of the axisymmetric magnetic field dynamo waves. It was found that, the magnetic configuration of the star dominates by the regular nonaxisymmetric mode m=1, forming Yin Yang magnetic polarity pattern with the strong (>500 G) poloidal magnetic field in polar regions.

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

Cited by 14 publications

References 41 publications

A New Simple Dynamo Model for Stellar Activity Cycle

A New Simple Dynamo Model for Stellar Activity Cycle

Nonkinematic solar dynamo models with double-cell meridional circulation

Non-linear regimes in mean-field full-sphere dynamo

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