Excitation of non-axially symmetric modes of the Sun's mean magnetic field

Ruzmaikin, A.; Sokoloff, Dmitry; Старченко, С. В.

doi:10.1007/bf00146226

Cited by 24 publications

(13 citation statements)

References 11 publications

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“…Non-axisymmetric α 2 Ω mean-field models also suggest a lower critical dynamo number for non-axisymmetric dynamo modes (e.g. Ruzmaikin et al 1988;Bassom et al 2005). These findings may explain the onset of the new larger wave number magnetic mode in our strongly stratified cases.…”

Section: Influence Of Stratificationsupporting

confidence: 54%

Dipolar versus multipolar dynamos: the influence of the background density stratification

Gastine

Duarte

Wicht

2012

A&A

109

110

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Context. Dynamo action in giant planets and rapidly rotating stars leads to a broad variety of magnetic field geometries including small-scale multipolar and large-scale dipole-dominated topologies. Previous dynamo models suggest that solutions become multipolar once inertia is influential. Being tailored for terrestrial planets, most of these models neglected the background density stratification. Aims. We investigate the influence of the density stratification on convection-driven dynamo models. Methods. Three-dimensional nonlinear simulations of rapidly rotating spherical shells were employed using the anelastic approximation to incorporate density stratification. A systematic parametric study for various density stratifications and Rayleigh numbers at two different aspect ratios allowed us to explore the dependence of the magnetic field topology on these parameters. Results. Anelastic dynamo models tend to produce a broad range of magnetic field geometries that fall on two distinct branches with either strong dipole-dominated or weak multipolar fields. As long as inertia is weak, both branches can coexist, but the dipolar branch vanishes once inertia becomes influential. The dipolar branch also vanishes for stronger density stratifications. The reason is that the convective columns are concentrated in a narrow region close to the outer boundary equator, a configuration that favors nonaxisymmetric solutions. In multipolar solutions, zonal flows can become significant and participate in the toroidal field generation. Parker-dynamo waves may then play an important role close to onset of dynamo action, leading to a cyclic magnetic field behavior. Conclusions. These results are compatible with the magnetic fields of gas planets that are likely generated in their deeper conducting envelopes where the density stratification is only mild. Our simulations also suggest that the dipolar or multipolar magnetic fields of late M dwarfs can be explained in two ways. They may differ either because of the relative influence of inertia or fall into the regime where both types of solutions coexist.

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Section: Influence Of Stratificationsupporting

confidence: 54%

Dipolar versus multipolar dynamos: the influence of the background density stratification

Gastine

Duarte

Wicht

2012

A&A

109

110

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“…The present approach is different from the one used by Ruzmaikin et al (1988). They implicitly assumed that the maxima of the generation sources and the maxima of the solution coincide with each other, and obtained conditions to determine the constant Γ and the functions S in the form of power‐series expansions up to the second‐order terms.…”

Section: The Asymptotic Solutionmentioning

confidence: 99%

“…They assumed that the maximum of the asymptotic solution coincides with the maximum of the sources of the field generation. Ruzmaikin & Starchenko (1988), Ruzmaikin, Sokoloff & Starchenko (1988) and also Makarov, Ruzmaikin & Starchenko (1987) considered α Ω dynamo models in the framework of asymptotic WKBJ methods in the strong‐generation limiting case. Such a short‐wave approximation approach had problems with the calculation of the solution near the so‐called turning points, and the fact that the dynamo equations are rather different from the well‐studied quantum mechanics equations did not allow researchers to apply standard methods uniformly.…”

Section: Introductionmentioning

confidence: 99%

A two-dimensional asymptotic solution for a dynamo wave in the light of the solar internal rotation

Belvedère

Kuzanyan

Sokoloff

2000

Monthly Notices of the Royal Astronomical Society

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A B S T R A C TThe mean field dynamo equations for a two-dimensional (radius±latitude) aV model are solved in the leading order of asymptotic expansion by the use of a WKBJ method. The limiting case of short waves (large regeneration rate) is considered. The solution is shown to possess properties of travelling dynamo waves obeying Yoshimura's law. Indeed, the dynamo wave propagates along lines of constant angular velocity. This solution is compared with the one obtained for the one-dimensional model and with observational results for solar large-scale magnetic activity.The internal differential rotation, deduced from helioseismological data, is represented by an analytic fitting function. Specific locations of the dynamo wave maxima and reversals calculated in this approximation, using both the one-dimensional model and the paraboloidal approximation of the two-dimensional model, are shown to be close to each other.In our approach two non-overlapping independent dynamo waves are obtained. The first wave propagates equatorwards over low latitudes, while the second one propagates polewards over high latitudes. The wave maxima are located at the bottom of the convection zone.

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“… The possibility of preferable generation of a non‐axisymmetric solution by an αΩ‐ or α 2 Ω‐dynamo was discussed previously (see e.g. Ruzmaikin, Sokoloff & Starchenko 1988), however such models require very specific configurations of rotation and helicity in order to reduce the destructive effect of differential rotation on the non‐axisymmetric field. …”

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confidence: 99%

Swing excitation and magnetic activity in close binary systems

Sokoloff

Piskunov

2002

Monthly Notices of the Royal Astronomical Society

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Parametric resonance between the perturbation of a stellar convective zone affected by a companion of a close binary system and non‐axisymmetric dynamo modes can play an important role in close binary systems. This process in combination with the previously suggested α2‐mechanism is probably responsible for strongly non‐axisymmetric magnetic activity observed in several close binaries. The conditions required for swing excitation to occur in such systems are directly related to the status of rotational synchronization between the orbital motion and rotation of the star, which can be used as a tool to discover such objects. One potential candidate – an active RS CVn‐type star ER Vulpeculae – shows indications of the swing excitation.

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Excitation of non-axially symmetric modes of the Sun's mean magnetic field

Cited by 24 publications

References 11 publications

Dipolar versus multipolar dynamos: the influence of the background density stratification

Dipolar versus multipolar dynamos: the influence of the background density stratification

A two-dimensional asymptotic solution for a dynamo wave in the light of the solar internal rotation

Swing excitation and magnetic activity in close binary systems

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