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

Пипин, В. В.

doi:10.1093/mnras/stw3182

Cited by 22 publications

(28 citation statements)

References 69 publications

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“…This coexistence confirms the mean-field calculation (e.g. Rädler et al 1990;Elstner & Rüdiger 2007;Pipin 2017), where an anisotropic α tensor can generate non-axisymmetric fields.…”

Section: Anisotropy Of the α Tensorsupporting

confidence: 88%

Turbulent transport coefficients in spherical wedge dynamo simulations of solar-like stars

Warnecke

Rheinhardt

Tuomisto

et al. 2018

A&A

130

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Context. For moderate and slow rotation, magnetic activity of solar-like stars is observed to strongly depend on rotation, while for rapid rotation, only a very weak or no dependency is detected. These observations do not yet have a solid explanation in terms of dynamo theory. Aims. To work towards such an explanation, we numerically investigated the rotational dependency of dynamo drivers in solar-like stars, that is, stars that have a convective envelope of similar thickness as in the Sun. Methods. We ran semi-global convection simulations of stars with rotation rates from 0 to 30 times the solar value, corresponding to Coriolis numbers, Co, of 0 to 110. We measured the turbulent transport coefficients describing the magnetic field evolution with the help of the test-field method, and compared with the dynamo effect arising from the differential rotation, self-consistently generated in the models.Results. The trace of the α tensor increases for moderate rotation rates with Co 0.5 and levels off for rapid rotation. This behavior is in agreement with the kinetic α based on the kinetic helicity, if one takes into account the decrease of the convective scale with increasing rotation. The α tensor becomes highly anisotropic for Co 1, α rr dominates for moderate rotation (1

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“…This coexistence confirms the mean-field calculation (e.g. Rädler et al 1990;Elstner & Rüdiger 2007;Pipin 2017), where an anisotropic α tensor can generate non-axisymmetric fields.…”

Section: Anisotropy Of the α Tensorsupporting

confidence: 88%

Turbulent transport coefficients in spherical wedge dynamo simulations of solar-like stars

Warnecke

Rheinhardt

Tuomisto

et al. 2018

A&A

130

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“…This is a layer in the top 40 Mm of the Sun, where ∂Ω/∂r < 0, which causes equatorward migrating dynamo waves when α is positive in the northern hemisphere (Brandenburg 2005a). Such a dynamo model has been developed by and Pipin (2017). Cameron & Schüssler (2017) have presented an updated version of the one-dimensional phenomenological dynamo model of Leighton (1969) by including a number of effects such as the evolution of the radially integrated toroidal magnetic field, the latitudinal variation of the surface angular velocity, turbulent downward pumping, and several other features.…”

Section: The Solar Dynamo Dilemmamentioning

confidence: 99%

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

Brandenburg

2018

J. Plasma Phys.

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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 provided some of the main new qualitative and quantitative 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 on dynamo theory are still less stringent and more uncertain, but recent advances both in theory and observations suggest that more conclusive comparisons may soon be possible also here. The possibility of inversely cascading magnetic helicity in the early Universe is particularly exciting in explaining the recently observed lower limits of magnetic fields on cosmological length scales. Such magnetic fields may be helical with the same sign of magnetic helicity throughout the entire Universe. This would be a manifestation of parity breaking. † Email address for correspondence: brandenb@nordita.org † In the following, we continue using the lowercase symbols u and b instead of U ′ and B ′ to denote fluctuations of U and B.

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“…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%

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

Cited by 22 publications

References 69 publications

Turbulent transport coefficients in spherical wedge dynamo simulations of solar-like stars

Turbulent transport coefficients in spherical wedge dynamo simulations of solar-like stars

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

Nonkinematic solar dynamo models with double-cell meridional circulation

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