Magnetoconvection and dynamo coefficients: Dependence of the alpha-effect on rotation and magnetic field

Abstract

We present numerical simulations of three-dimensional compressible magnetoconvection in a rotating rectangular box that represents a section of the solar convection zone. The box contains a convectively unstable layer, surrounded by stably stratified layers with overshooting convection. The magnetic Reynolds number, Rm, is chosen subcritical, thus excluding spontaneous growth of the magnetic field through dynamo action, and the magnetic energy is maintained by introducing a constant magnetic field into the box, once convection has attained a statistically stationary state. Under the influence of the Coriolis force, the advection of the magnetic field results in a non-vanishing contribution to the mean electric field, given by uxb. From this electric field, we calculate the alpha-effect, separately for the stably and the unstably stratified layers, by averaging over time and over suitably defined volumes. From the variation of alpha we derive an error estimate, and the dependence of alpha on rotation and magnetic field strength is studied. Evidence is found for rotational quenching of the vertical alpha-effect, and for a monotonic increase of the horizontal alpha-effect with increasing rotation. For Rm~30, our results for both vertical and horizontal alpha-effect are consistent with magnetic quenching by a factor 1/[1+Rm(B_0/B_eq)^2]. The signs of the small-scale current helicity and of the vertical component of alpha are found to be opposite to those for isotropic turbulence.

14 pages, 11 figures; to appear in Astronomy & Astrophysics (accepted)

References in corpus (1)

• Large scale dynamos with helicity loss through boundaries

Cited by in corpus (41)

• Astrophysical magnetic fields and nonlinear dynamo theory
• Simulations of stellar convection with CO5BOLD
• The solar magnetic field
• Magnetic field generation in fully convective rotating spheres
• Large-scale dynamos in turbulent convection with shear
• Magnetoconvection and dynamo coefficients: II. Field-direction dependent pumping of magnetic field
• Local and nonlocal magnetic diffusion and alpha-effect tensors in shear flow turbulence
• Alpha effect and turbulent diffusion from convection
• Advances in mean-field dynamo theory and applications to astrophysical turbulence
• Hemispheric Coupling: Comparing Dynamo Simulations and Observations
• Local models of stellar convection: Reynolds stresses and turbulent heat transport
• Large-scale dynamos in rigidly rotating turbulent convection
• Catastrophic alpha quenching alleviated by helicity flux and shear
• Magnetoconvection and dynamo coefficients III: alpha-effect and magnetic pumping in the rapid rotation regime
• Turbulent transport coefficients in spherical wedge dynamo simulations of solar-like stars
• Quenching and anisotropy of hydromagnetic turbulent transport
• Solar dynamo models with alpha-effect and turbulent pumping from local 3D convection calculations
• Do spherical alpha^2-dynamos oscillate?
• The mean-field solar dynamo with double cell meridional circulation pattern
• Geodynamo alpha-effect derived from box simulations of rotating magnetoconvection
• Effects of a subadiabatic layer on convection and dynamos in spherical wedge simulations
• Effect of Rotation on a Developed Turbulent Stratified Convection: the Hydrodynamic Helicity, the Alpha-Effect and the Effective Drift Velocity
• Oscillating α^2-dynamos and the reversal phenomenon of the global geodynamo
• On the problem of large-scale magnetic field generation in rotating compressible convection
• Ejections of magnetic structures above a spherical wedge driven by a convective dynamo with differential rotation
• Turbulent processes and mean-field dynamo
• Helicity conservation in nonlinear mean-field solar dynamo
• The origin of the helicity hemispheric sign rule reversals in the mean-field solar-type dynamo
• Effects of turbulent pumping on stellar activity cycles
• The problem of small and large scale fields in the solar dynamo
• Compressible test-field method and its application to shear dynamos
• The cross helicity at the solar surface by simulations and observations
• On global solar dynamo simulations
• An advective solar-type dynamo without the alpha effect
• An efficient method for computing the eigenfunctions of the dynamo equation
• The alpha-effect and current helicity for fast sheared rotators
• Importance of magnetic helicity in dynamos
• Alpha tensor and dynamo excitation in turbulent fluids with anisotropic conductivity fluctuations
• Electrodynamics of turbulent fluids with fluctuating electric conductivity
• Solar-like dynamos and rotational scaling of cycles from star-in-a-box simulations
• Angular momentum transport by magnetoconvection and the magnetic modulation of the solar differential rotation