Global-Scale Turbulent Convection and Magnetic Dynamo Action in the Solar Envelope

Abstract

The operation of the solar global dynamo appears to involve many dynamical elements. Self-consistent MHD simulations which realistically incorporate all of these processes are not yet computationally feasible, though some elements can now be studied with reasonable fidelity. Here we consider the manner in which turbulent compressible convection within the bulk of the solar convection zone can generate large-scale magnetic fields through dynamo action. We accomplish this through a series of three-dimensional numerical simulations of MHD convection within rotating spherical shells using our ASH code on massively parallel supercomputers. Since differential rotation is a key ingredient in all dynamo models, we also examine here the nature of the rotation profiles that can be sustained within the deep convection zone as strong magnetic fields are built and maintained. We find that the convection is able to maintain a solar-like angular velocity profile despite the influence of Maxwell stresses which tend to oppose Reynolds stresses and thus reduce the latitudinal angular velocity contrast throughout the convection zone. The dynamo-generated magnetic fields exhibit a complex structure and evolution, with radial fields concentrated in downflow lanes and toroidal fields organized into twisted ribbons which are extended in longitude and which achieve field strengths of up to 5000 G. The flows and fields exhibit substantial kinetic and magnetic helicity although systematic hemispherical patterns are only apparent in the former. Fluctuating fields dominate the magnetic energy and account for most of the back-reaction on the flow via Lorentz forces. Mean fields are relatively weak and do not exhibit systematic latitudinal propagation or periodic polarity reversals as in the sun. This may be attributed to the absence of a tachocline.

55 pages (ApJ refereeing format), 15 figures (low res), published by ApJ on October 2004 (abstract slightly reduced in order to fit in 24 lines limit) see also Browning, Miesch, Brun & Toomre 2006, ApJL, 648, 157 (astro-ph/0609153) for the effect of a tachocline in organizing the mean fields

References in corpus (1)

• Nonlinear current helicity fluxes in turbulent dynamos and alpha quenching

Cited by in corpus (17)

• The case for a distributed solar dynamo shaped by near-surface shear
• Toroidal versus poloidal magnetic fields in Sun-like stars: a rotation threshold
• Magnetic field generation in fully convective rotating spheres
• Simulations of core convection in rotating A-type stars: Magnetic dynamo action
• Magnetic confinement of the solar tachocline
• Large-scale dynamos in turbulent convection with shear
• On the role of meridional flows in flux transport dynamo models
• Simulations of turbulent convection in rotating young solar-like stars: Differential rotation and meridional circulation
• Advances in theory and simulations of large-scale dynamos
• Effect of the radiative background flux in convection
• 3-D non-linear evolution of a magnetic flux tube in a spherical shell: the isentropic case
• Structure of the near-surface layers of the Sun: asphericity and time variation
• Rapid Rotation, Active Nests of Convection and Global-scale Flows in Solar-like Stars
• Planetary dynamos
• Paradigm shifts in solar dynamo modeling
• Wave propagation in the magnetic sun
• The solar interior - radial structure, rotation, solar activity cycle