The mean electro-motive force and current helicity under the influence of rotation, magnetic field and shear

Пипин, В. В.

doi:10.1080/03091920701374772

Cited by 54 publications

(83 citation statements)

References 25 publications

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“…As discussed throughout the work, all results of RS06 are recovered in the limit ∇ ln ρ = 0 [aside from one discrepancy, in (β (D) ) u ]. This agrees with Rüdiger and Kitchatinov [18], many results of Pipin [11], including his magnetic contributions (see his Appendix B), as well as the quasilinear methods in Sridhar and Subramanian [39] and Singh and Sridhar [21]. As is well known, there is a discrepancy between these kinematic quasilinear results and those obtained using the τ approximation [9,17], possibly due to a change in sign of η yx with Rm [20].…”

Section: Agreement With Previous Worksupporting

confidence: 60%

“…[9,10,30,31,37]. In a very general calculation, Pipin [11] nonlinearly includes all effects discussed here (although the approach, the "minimal τ approximation," has a somewhat unknown range of validity). We have also computed the magnetic dynamo transport coefficients with nonperturbative shear and rotation using statistical simulation in the shearing box [12].…”

Section: B Perturbation Expansion To Describe the Fluctuationsmentioning

confidence: 99%

“…Of particular note is the presence of homogeneous magnetic fluctuations, which have not been included in most previous theoretical mean-field dynamo investigations (but see Vainshtein and Kichatinov [7] and Pouquet et al [8] for early treatments, as well as Refs. [9][10][11]). Magnetic fluctuations should be generically present, at a similar level to velocity fluctuations, in magnetohydrodynamic (MHD) turbulence above moderate Reynolds numbers due to smallscale dynamo action.…”

Section: Introductionmentioning

confidence: 99%

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Electromotive force due to magnetohydrodynamic fluctuations in sheared rotating turbulence

Squire¹,

Bhattacharjee²

2015

Phys. Rev. E

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This article presents a calculation of the mean electromotive force arising from general small-scale magnetohydrodynamical turbulence, within the framework of the second-order correlation approximation. With the goal of improving understanding of the accretion disk dynamo, effects arising through small-scale magnetic fluctuations, velocity gradients, density and turbulence stratification, and rotation, are included. The primary result, which supplements numerical findings, is that an off-diagonal turbulent resistivity due to magnetic fluctuations can produce large-scale dynamo action-the magnetic analog of the "shear-current" effect. In addition, consideration of α effects in the stratified regions of disks gives the puzzling result that there is no strong prediction for a sign of α, since the effects due to kinetic and magnetic fluctuations, as well as those due to shear and rotation, are each of opposing signs and tend to cancel each other.

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Section: Agreement With Previous Worksupporting

confidence: 60%

Section: B Perturbation Expansion To Describe the Fluctuationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Electromotive force due to magnetohydrodynamic fluctuations in sheared rotating turbulence

Squire¹,

Bhattacharjee²

2015

Phys. Rev. E

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“…In this case the shear-current dynamo acts together with the α-shear dynamo which is similar to the αΩ dynamo. The joint action of the shear-current and the α-shear dynamos have been recently discussed in [16,39,40]. The shear-current effect does not quenched (see [11,16]) contrary to the quenching of the nonlinear α effect, the turbulent magnetic diffusion, the effective drift velocity, etc.…”

Section: Discussionmentioning

confidence: 99%

Shear-current effect in a turbulent convection with a large-scale shear

Rogachevskii

Kleeorin

2007

Phys. Rev. E

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The shear-current effect in a nonrotating homogeneous turbulent convection with a large-scale constant shear is studied. The large-scale velocity shear causes anisotropy of turbulent convection, which produces the mean electromotive force E (W ) ∝ W×J and the mean electric current along the original mean magnetic field, where W is the background mean vorticity due to the shear and J is the mean electric current. This results in a large-scale dynamo even in a nonrotating and nonhelical homogeneous sheared turbulent convection, whereby the α effect vanishes. It is found that turbulent convection promotes the shear-current dynamo instability, i.e., the heat flux causes positive contribution to the shear-current effect. However, there is no dynamo action due to the shear-current effect for small hydrodynamic and magnetic Reynolds numbers even in a turbulent convection, if the spatial scaling for the turbulent correlation time is τ (k) ∝ k −2 , where k is the small-scale wave number.

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“…Our model includes the anisotropy of turbulent transport induced by rotation. The rather complicated expression for EMF for rotating fluids (Pipin 2008) can be split in three relatively simple parts representing physically different effects of turbulent diffusion (E diff ), diamagnetic pumping (E dia ), and the α-effect (E α ):…”

Section: Dynamo Modelmentioning

confidence: 99%

How supercritical are stellar dynamos, or why do old main-sequence dwarfs not obey gyrochronology?

Kitchatinov

Nepomnyashchikh

2017

Monthly Notices of the Royal Astronomical Society

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Asteroseismological determinations of stellar ages have shown that old main-sequence dwarfs do not obey gyrochronology. Their rotation is slow compared to young stars but faster than gyrochronology predicts. This can be explained by the presence of a maximum rotation period beyond which the large-scale dynamo switches off and stops providing global magnetic fields necessary for stellar spindown. Assuming this explanation, the excess of stellar dynamo parameters over their marginal values can be estimated for given spectral type and rotation rate. The estimation gives the dynamo number for the Sun about 10% above its critical value. The corresponding dynamo model provides -though with some further tuning -reasonable results for the Sun. Following the same approach, the differential rotation and marginal dynamo modes are computed for stars between 0.7 and 1.2 solar masses. With increasing stellar mass, the differential rotation and the ratio of toroidal-to-poloidal field are predicted to increase while the field topology changes from dipolar to mixed quadrupolar-dipolar parity.

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The mean electro-motive force and current helicity under the influence of rotation, magnetic field and shear

Cited by 54 publications

References 25 publications

Electromotive force due to magnetohydrodynamic fluctuations in sheared rotating turbulence

Electromotive force due to magnetohydrodynamic fluctuations in sheared rotating turbulence

Shear-current effect in a turbulent convection with a large-scale shear

How supercritical are stellar dynamos, or why do old main-sequence dwarfs not obey gyrochronology?

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