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Mesogranulation and small-scale dynamo action in the quiet Sun

Lookup NU author(s): Dr Paul Bushby

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This is the final published version of an article that has been published in its final definitive form by EDP Sciences, 2014.

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Abstract

Context: Regions of quiet Sun generally exhibit a complex distribution of small-scale magnetic field structures, which interact with the near-surface turbulent convective motions. Furthermore, it is probable that some of these magnetic fields are generated locally by a convective dynamo mechanism. In addition to the well-known granular and supergranular convective scales, various observations have indicated that there is an intermediate scale of convection, known as mesogranulation, with vertical magnetic flux concentrations accumulating preferentially at the boundaries of mesogranules. Aims: Our aim is to investigate the small-scale dynamo properties of a convective flow that exhibits both granulation and mesogranulation, comparing our findings with solar observations. Methods: Adopting an idealised model for a localised region of quiet Sun, we use numerical simulations of compressible magnetohydrodynamics, in a three-dimensional Cartesian domain, to investigate the parametric dependence of this system (focusing particularly upon the effects of varying the aspect ratio and the Reynolds number). Results: In purely hydrodynamic convection, we find that mesogranulation is a robust feature of this system provided that the domain is wide enough to accommodate these large-scale motions. The mesogranular peak in the kinetic energy spectrum is more pronounced in the higher Reynolds number simulations. We investigate the dynamo properties of this system in both the kinematic and the nonlinear regimes and we find that the dynamo is always more efficient in larger domains, when mesogranulation is present. Furthermore, we use a filtering technique in Fourier space to demonstrate that it is indeed the larger scales of motion that are primarily responsible for driving the dynamo. In the nonlinear regime, the magnetic field distribution compares very favourable to observations, both in terms of the spatial distribution and the measured field strengths.


Publication metadata

Author(s): Bushby PJ, Favier B

Publication type: Article

Publication status: Published

Journal: Astronomy & Astrophysics

Year: 2014

Volume: 562

Print publication date: 01/02/2014

Acceptance date: 16/01/2014

Date deposited: 10/02/2014

ISSN (print): 0004-6361

ISSN (electronic): 1432-0746

Publisher: EDP Sciences

URL: http://dx.doi.org/10.1051/0004-6361/201322993

DOI: 10.1051/0004-6361/201322993


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