Box simulations of rotating magnetoconvection

Ziegler, Udo; Rüdiger, G.

doi:10.1051/0004-6361:20030207

Cited by 51 publications

(44 citation statements)

References 18 publications

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“…(Ossendrijver et al 2002;Käpylä et al 2006a) and other diagnostics (e.g. Nordlund et al 1992;Tobias et al 1998Tobias et al , 2001Ziegler & Rüdiger 2003). However, this result is obtained for test fields for which k/k 1 = 1, whereas the imposed field results use a uniform field with k/k 1 = 0.…”

Section: Resultsmentioning

confidence: 89%

Alpha effect and turbulent diffusion from convection

Käpylä¹,

Korpi²,

Brandenburg

2009

A&A

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Aims. We study turbulent transport coefficients that describe the evolution of large-scale magnetic fields in turbulent convection. Methods. We use the test field method, together with three-dimensional numerical simulations of turbulent convection with shear and rotation, to compute turbulent transport coefficients describing the evolution of large-scale magnetic fields in mean-field theory in the kinematic regime. We employ one-dimensional mean-field models with the derived turbulent transport coefficients to examine whether they give results that are compatible with direct simulations. Results. The results for the α-effect as a function of rotation rate are consistent with earlier numerical studies, i.e. increasing magnitude as rotation increases and approximately cos θ latitude profile for moderate rotation. Turbulent diffusivity, η t , is proportional to the square of the turbulent vertical velocity in all cases. Whereas η t decreases approximately inversely proportional to the wavenumber of the field, the α-effect and turbulent pumping show a more complex behaviour with partial or full sign changes and the magnitude staying roughly constant. In the presence of shear and no rotation, a weak α-effect is induced which does not seem to show any consistent trend as a function of shear rate. Provided that the shear is large enough, this small α-effect is able to excite a dynamo in the mean-field model. The coefficient responsible for driving the shear-current effect shows several sign changes as a function of depth but is also able to contribute to dynamo action in the mean-field model. The growth rates in these cases are, however, well below those in direct simulations, suggesting that an incoherent α-shear dynamo may also act in the simulations. If both rotation and shear are present, the α-effect is more pronounced. At the same time, the combination of the shear-current and Ω × J-effects is also stronger than in the case of shear alone, but subdominant to the α-shear dynamo. The results of direct simulations are consistent with mean-field models where all of these effects are taken into account without the need to invoke incoherent effects.

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Section: Resultsmentioning

confidence: 89%

Alpha effect and turbulent diffusion from convection

Käpylä¹,

Korpi²,

Brandenburg

2009

A&A

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“…Furthermore, the relative stability parameter S showed an S −1/4 dependence on the penetration distance implying the existence of a thermal adjustment region in the lower stable layer rather than a nearly adiabatic penetration zone. Ziegler & Rüdiger (2003) and Käpylä et al (2004), using their 3D MHD codes also found that, as a general feature, the overshooting at the bottom decreases as a function of increasing rotation at a given latitude. Browning et al (2004) performed three-dimensional simulations of core convection within A-type stars at a range of rotation rates.…”

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confidence: 89%

Turbulent compressible convection with rotation—penetration above a convection zone

Pal

Singh

Chan

et al. 2008

Astrophys Space Sci

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We perform Large eddy simulations of turbulent compressible convection in stellar-type convection zones by solving the Naviér-Stokes equations in three dimensions. We estimate the extent of penetration into the stable layer above a stellar-type convection zone by varying the rotation rate (Ω), the inclination of the rotation vector (θ) and the relative stability (S) of the upper stable layer The computational domain is a rectangular box in an f-plane configuration and is divided into two regions of unstable and stable stratification with the stable layer placed above the convectively unstable layer. Several models have been computed and the penetration distance into the stable layer above the convection zone is estimated by determining the position where time averaged kinetic energy flux has the first zero in the upper stable layer. The vertical grid spacing in all the model is non-uniform, and is less in the upper region so that the flows are better resolved in the region of interest. We find that the penetration distance increases as the rotation rate increases for the case when the rotation vector is aligned with the vertical axis. However, with the increase in the stability of the upper stable layer, the upward penetration distance decreases. Since we are not able to afford computations with finer resolution for all the models, we compute a number of models to see the effect of increased resolution on the upward penetration. In addition, we estimate the upper limit on the upward convective penetration from stellar convective cores.

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“…It has been argued that there the strong flux tubes are highly buoyant so that it is difficult for them to resist in the convection zone. However, the numerical simulations which are now possible lead to the opposite phenomenon: the mean magnetic flux is pumped downwards (Dorch & Nordlund 2001;Thomas et al 2002;Ossendrijver et al 2002;Ziegler & Rüdiger 2003). It seems indeed as would the downward pumping of the magnetic field be the most prominent feature of the rotating magnetoconvection (Nordlund et al 1992).…”

Section: Introductionmentioning

confidence: 96%

“…It seems indeed as would the downward pumping of the magnetic field be the most prominent feature of the rotating magnetoconvection (Nordlund et al 1992). On the other hand, the penetration depth of the overshooting convection into the stable region below the convection zone appears to be very small (see Ziegler & Rüdiger 2003). Moreover, the transition region itself where the differential rotation rapidly becomes uniform (the tachocline) appears to be hydrodynamically unstable (Arlt, Sule & Rüdiger 2005).…”

Section: Introductionmentioning

confidence: 99%

Advection‐dominated solar dynamo model with two‐cell meridional flow and a positive α ‐effect in the tachocline

Bonanno¹,

Elstner

Belvedère

2006

Astron Nachr

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Most probably the sunspot cycle period is ruled by a meridional flow located near the base of the convection zone (Hathaway et al. 2003). On the other hand, if the eddy diffusivity is low enough, dramatic modification of the standard α 2 Ω-dynamo by the meridional flow are expected. In this paper we shall discuss the dependence of periods, dynamo numbers and the sign of the current helicity as a function of the magnetic Reynolds number for a double cell meridional circulation and for a positive α-effect at the base of the convection zone. The dynamo action occurs at lower latitudes and its location is at the interface between equatorward and poleward motions near the base of the convection zone. In spite of the complexity of the flow pattern, our simulations show that the resulting dynamo action reproduces several observed features of the solar cycle.

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Box simulations of rotating magnetoconvection

Cited by 51 publications

References 18 publications

Alpha effect and turbulent diffusion from convection

Alpha effect and turbulent diffusion from convection

Turbulent compressible convection with rotation—penetration above a convection zone

Advection‐dominated solar dynamo model with two‐cell meridional flow and a positive α ‐effect in the tachocline

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