Estimating the rate of field line braiding in the solar corona by photospheric flows

Candelaresi, S. , Pontin, D.I., Yeates, A.R., Bushby, P.J. and Hornig, G. (2018) Estimating the rate of field line braiding in the solar corona by photospheric flows. Astrophysical Journal, 864(2), 157. (doi: 10.3847/1538-4357/aad8bc)

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In this paper, we seek to understand the timescale in which the photospheric motions on the Sun braid coronal magnetic field lines. This is a crucial ingredient for determining the viability of the braiding mechanism for explaining the high temperatures observed in the corona. We study the topological complexity induced in the coronal magnetic field, primarily using plasma motions extracted from magneto-convection simulations. This topological complexity is quantified using the field line winding, finite time topological entropy (FTTE), and passive scalar mixing. With these measures, we contrast mixing efficiencies of the magneto-convection simulation, a benchmark flow known as a "blinking vortex", and finally photospheric flows inferred from sequences of observed magnetograms using local correlation tracking. While the highly resolved magneto-convection simulations induce a strong degree of field line winding and FTTE, the values obtained from the observations from the plage region are around an order of magnitude smaller. This behavior is carried over to the FTTE. Nevertheless, the results suggest that the photospheric motions induce complex tangling of the coronal field on a timescale of hours.

Item Type:Articles
Additional Information:S.C., D.I.P., A.R.Y., and G.H. acknowledge financial support from the UK’s STFC (grant Nos. ST/N000714 and ST/N000781). P.B. would like to acknowledge the support of the Leverhulme Trust (grant No. RPG-2014-427).
Glasgow Author(s) Enlighten ID:Candelaresi, Dr Simon
Authors: Candelaresi, S., Pontin, D.I., Yeates, A.R., Bushby, P.J., and Hornig, G.
College/School:College of Science and Engineering > School of Mathematics and Statistics > Mathematics
Journal Name:Astrophysical Journal
Publisher:American Astronomical Society
ISSN (Online):1538-4357
Published Online:12 September 2018
Copyright Holders:Copyright © 2018 The American Astronomical Society
First Published:First published in Astrophysical Journal 864(2): 157
Publisher Policy:Reproduced under a Creative Commons License

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