Effect of solar chromospheric neutrals on equilibrium field structures

Arber, Tony, Botha, Gert and Brady, Christopher S. (2009) Effect of solar chromospheric neutrals on equilibrium field structures. The Astrophysical Journal, 705 (2). pp. 1183-1188. ISSN 0004-637X

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Official URL: http://dx.doi.org/10.1088/0004-637X/705/2/1183

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 alpha 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: Article
Subjects: F300 Physics
F500 Astronomy
G900 Others in Mathematical and Computing Sciences
Department: Faculties > Engineering and Environment > Mathematics and Information Sciences
Depositing User: Gert Botha
Date Deposited: 05 Apr 2013 09:40
Last Modified: 16 May 2017 05:32
URI: http://nrl.northumbria.ac.uk/id/eprint/11952

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