ON THE MODE OF DYNAMO ACTION IN A GLOBAL LARGE-EDDY SIMULATION OF SOLAR CONVECTION

Journal Article · Fri Jul 01 00:00:00 EDT 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/735/1/46· OSTI ID:21576532

Racine, Etienne ^[1]; Charbonneau, Paul; Ghizaru, Mihai; Bouchat, Amelie ^[2]; Smolarkiewicz, Piotr K ^[3]

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1. Canadian Space Agency, St-Hubert, Quebec (Canada)
2. Departement de Physique, Universite de Montreal, C.P. 6128 Succ. Centre-ville, Montreal, Qc H3C-3J7 (Canada)
3. National Center for Atmospheric Research, Boulder, CO 80307 (United States)

In this paper, we examine the mode of dynamo action in the implicit large-eddy magnetohydrodynamical simulation of solar convection reported upon in Ghizaru et al. Motivated by the presence of a strong and well-defined large-scale axisymmetric magnetic component undergoing regular polarity reversals, we define the fluctuating component of the magnetic field as the difference between the total field and its zonal average. The subsequent analysis follows the physical logic and mathematical formulation of mean-field electrodynamics, whereby a turbulent electromotive force (EMF) is computed by the suitable averaging of cross-correlations between fluctuating flow and field components and expressed in terms of the mean field via a linear truncated tensorial expansion. We use singular value decomposition to perform a linear least-squares fit of the temporal variation of the EMF to that of the large-scale magnetic component, which yields the components of the full {alpha}-tensor. Its antisymmetric component, describing general turbulent pumping, is also extracted. The {alpha}-tensor so calculated reproduces a number of features already identified in local, Cartesian simulations of magnetohydrodynamical rotating convection, including an {alpha}{sub {phi}{phi}} component positive in the northern solar hemisphere, peaking at high latitudes, and reversing sign near the bottom of the convection zone; downward turbulent pumping throughout the convecting layer; and significant equatorward turbulent pumping at mid latitudes, and poleward at high latitudes in subsurface layers. We also find that the EMF contributes significantly to the regeneration of the large-scale toroidal magnetic component, which from the point of view of mean-field dynamo models would imply that the simulation operates as an {alpha}{sup 2}{Omega} dynamo. We find little significant evidence of {alpha}-quenching by the large-scale magnetic field. The amplitude of the magnetic cycle appears instead to be regulated primarily by a magnetically driven reduction of the differential rotation.

• OSTI ID: 21576532
• Journal Information: Astrophysical Journal, Vol. 735, Issue 1; Other Information: DOI: 10.1088/0004-637X/735/1/46; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
CONVECTION
ELECTROMOTIVE FORCE
LARGE-EDDY SIMULATION
LEAST SQUARE FIT
MAGNETIC FIELDS
MAGNETOHYDRODYNAMICS
MEAN-FIELD THEORY
ROTATION
SUN
COMPUTERIZED SIMULATION
ENERGY TRANSFER
FLUID MECHANICS
HEAT TRANSFER
HYDRODYNAMICS
MAIN SEQUENCE STARS
MASS TRANSFER
MATHEMATICAL SOLUTIONS
MAXIMUM-LIKELIHOOD FIT
MECHANICS
MOTION
NUMERICAL SOLUTION
SIMULATION
STARS