The case for a distributed solar dynamo shaped by near-surface shear

Abstract

Arguments for and against the widely accepted picture of a solar dynamo being seated in the tachocline are reviewed and alternative ideas concerning dynamos operating in the bulk of the convection zone, or perhaps even in the near-surface shear layer, are discussed. Based on the angular velocities of magnetic tracers it is argued that the observations are compatible with a distributed dynamo that may be strongly shaped by the near-surface shear layer. Direct simulations of dynamo action in a slab with turbulence and shear are presented to discuss filling factor and tilt angles of bipolar regions in such a model.

10 pages, 6 figures, Astrophys. J. 625 (scheduled for the 1 June 2005 issue)

References in corpus (22)

• The inverse cascade and nonlinear alpha-effect in simulations of isotropic helical hydromagnetic turbulence
• Simulations of small-scale turbulent dynamo
• Global-Scale Turbulent Convection and Magnetic Dynamo Action in the Solar Envelope
• Simulations of nonhelical hydromagnetic turbulence
• Magnetic Helicity Conservation and Astrophysical Dynamos
• Deeply penetrating banded zonal flows in the solar convection zone
• Full--Sphere Simulations of a Circulation--Dominated Solar Dynamo: Exploring the Parity Issue
• Constraints on the magnitude of alpha in dynamo theory
• On magnetic field generation in Kolmogorov turbulence
• Electromotive Force and Large-Scale Magnetic Dynamo in a Turbulent Flow with a Mean Shear
• An Incoherent $\alpha -\Omega$ Dynamo in Accretion Disks
• Nonlinear theory of a "shear-current" effect and mean-field magnetic dynamos
• Solar supergranulation as a wavelike phenomenon
• Magnetoconvection and dynamo coefficients: II. Field-direction dependent pumping of magnetic field
• The subsurface radial gradient of solar angular velocity from MDI f-mode observations
• Critical Magnetic Prandtl Number for Small-Scale Dynamo
• Nonlinear current helicity fluxes in turbulent dynamos and alpha quenching
• The Interaction of New and Old Magnetic Fluxes at the Beginning of Solar Cycle 23
• Magnetic Helicity Evolution During the Solar Activity Cycle: Observations and Dynamo Theory
• Catastrophic alpha quenching alleviated by helicity flux and shear
• The helicity constraint in turbulent dynamos with shear
• The problem of small and large scale fields in the solar dynamo

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• Near-polytropic simulations with a radiative surface
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• Explaining the Observed Relation Between Stellar Activity and Rotation
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