Arber, T. D., Botha, G. J. J. and Brady, Christopher S. (2009) Effect of solar chromospheric neutrals on equilibrium field structures. Astrophysical Journal, Vol.705 (No.2). pp. 1183-1188. doi:10.1088/0004-637X/705/2/1183

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Abstract

Solar coronal equilibrium fields are often constructed by nonlinear force-free field (NLFFF) extrapolation from photospheric magnetograms. It is well known that the photospheric field is not force-free and the correct lower boundary for NLFFF construction ought to be the top of the chromosphere. To compensate for this, pre-filtering algorithms are often applied to the photospheric data to remove the non-force-free components. Such pre-filtering models, while physically constrained, do not address the mechanisms that may be responsible for the field becoming force-free. The chromospheric field can change through, for example, field expansion due to gravitational stratification, reconnection, or flux emergence. In this paper, we study and quantify the effect of the chromospheric neutrals on equilibrium field structures. It is shown that, depending on the degree to which the photospheric field is not force-free, the chromosphere will change the structure of the equilibrium field. This is quantified to give an estimate of the change in a profiles one might expect due to neutrals in the chromosphere. Simple scaling of the decay time of non-force-free components of the magnetic field due to chromospheric neutrals is also derived. This is used to quantify the rate at which, or equivalent at which height, the chromosphere is expected to become force-free.

Item Type:	Journal Article
Subjects:	Q Science > QA Mathematics Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Faculty of Science > Physics
Library of Congress Subject Headings (LCSH):	Magnetohydrodynamics, Solar activity, Solar chromosphere, Solar magnetic fields
Journal or Publication Title:	Astrophysical Journal
Publisher:	IOP Publishing
ISSN:	0004-637X
Official Date:	10 November 2009
Dates:	Date Event 10 November 2009 Published
Volume:	Vol.705
Number:	No.2
Number of Pages:	6
Page Range:	pp. 1183-1188
DOI:	10.1088/0004-637X/705/2/1183
Status:	Peer Reviewed
Publication Status:	Published
Funder:	Science and Technology Facilities Council (Great Britain)

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