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Numerical simulations of rotating axisymmetric sunspots

Botha, GJJ, Busse, FH, Hurlburt, NE and Rucklidge, AM (2008) Numerical simulations of rotating axisymmetric sunspots. Monthly notices of the Royal Astronomical Society, 387 (4). 1445 - 1462 . ISSN 0035-8711

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Abstract

A numerical model of axisymmetric convection in the presence of a vertical magnetic flux bundle and rotation about the axis is presented. The model contains a compressible plasma described by the non-linear MHD equations, with density and temperature gradients simulating the upper layer of the Sun's convection zone. The solutions exhibit a central magnetic flux tube in a cylindrical numerical domain, with convection cells forming collar flows around the tube. When the numerical domain is rotated with a constant angular velocity, the plasma forms a Rankine vortex, with the plasma rotating as a rigid body where the magnetic field is strong, as in the flux tube, while experiencing sheared azimuthal flow in the surrounding convection cells, forming a free vortex. As a result, the azimuthal velocity component has its maximum value close to the outer edge of the flux tube. The azimuthal flow inside the magnetic flux tube and the vortex flow is prograde relative to the rotating cylindrical reference frame. A retrograde flow appears at the outer wall. The most significant convection cell outside the flux tube is the location for the maximum value of the azimuthal magnetic field component. The azimuthal flow and magnetic structure are not generated spontaneously, but decay exponentially in the absence of any imposed rotation of the cylindrical domain.

Item Type: Article
Copyright, Publisher and Additional Information: © 2008 Blackwell Publishing . This is an author produced version of a paper to be published in Monthly notices of the Royal Astronomical Society. Uploaded in accordance with the publisher's self-archiving policy.
Keywords: convection, MHD, Sun : magnetic fields, sunspots, magnetic-flux tubes, compressible convection, evolution, fields, flares, consequences, motions, corona
Institution: The University of Leeds
Academic Units: The University of Leeds > Faculty of Maths and Physical Sciences (Leeds) > School of Mathematics (Leeds) > Applied Mathematics (Leeds)
Depositing User: Symplectic Publications
Date Deposited: 08 Sep 2011 13:23
Last Modified: 15 Sep 2014 03:55
Published Version: http://dx.doi.org/10.1111/j.1365-2966.2008.13359.x
Status: Published
Publisher: Blackwell Publishing
Identification Number: 10.1111/j.1365-2966.2008.13359.x
URI: http://eprints.whiterose.ac.uk/id/eprint/43192

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