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Convective intensification of magnetic fields in the quiet Sun

Bushby, P.J., Houghton, S.M., Proctor, M.R.E. and Weiss, N.O. (2008) Convective intensification of magnetic fields in the quiet Sun. Monthly Notices of the Royal Astronomical Society, 387 (2). pp. 698-706. ISSN 1365-2966

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Abstract

Kilogauss-strength magnetic fields are often observed in intergranular lanes at the photosphere in the quiet Sun. Such fields are stronger than the equipartition field B_e, corresponding to a magnetic energy density that matches the kinetic energy density of photospheric convection, and comparable with the field B_p that exerts a magnetic pressure equal to the ambient gas pressure. We present an idealised numerical model of three-dimensional compressible magnetoconvection at the photosphere, for a range of values of the magnetic Reynolds number. In the absence of a magnetic field, the convection is highly supercritical and is characterised by a pattern of vigorous, time-dependent, “granular” motions. When a weak magnetic field is imposed upon the convection, magnetic flux is swept into the convective downflows where it forms localised concentrations. Unless this process is significantly inhibited by magnetic diffusion, the resulting fields are often much greater than B_e, and the high magnetic pressure in these flux elements leads to their being partially evacuated. Some of these flux elements contain ultra-intense magnetic fields that are significantly greater than B_p. Such fields are contained by a combination of the thermal pressure of the gas and the dynamic pressure of the convective motion, and they are constantly evolving. These ultra-intense fields develop owing to nonlinear interactions between magnetic fields and convection; they cannot be explained in terms of “convective collapse” within a thin flux tube that remains in overall pressure equilibrium with its surroundings.

Item Type: Article
Copyright, Publisher and Additional Information: © 2008 The Authors. This is an author produced version of a paper published in "Monthly Notices of the Royal Astronomical Society". Uploaded in accordance with the publisher's self-archiving policy.
Keywords: Convection, Magnetohydrodynamics, Solar granulation
Academic Units: The University of Leeds > Faculty of Maths and Physical Sciences (Leeds) > School of Mathematics (Leeds) > Applied Mathematics (Leeds)
Depositing User: Dr S M Houghton
Date Deposited: 07 Jul 2009 15:04
Last Modified: 08 Feb 2013 17:06
Published Version: http://dx.doi.org/10.1111/j.1365-2966.2008.13276.x
Status: Published
Publisher: Wiley-Blackwell
Refereed: Yes
Identification Number: 10.1111/j.1365-2966.2008.13276.x
URI: http://eprints.whiterose.ac.uk/id/eprint/8905

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