Cookies

We use cookies to ensure that we give you the best experience on our website. By continuing to browse this repository, you give consent for essential cookies to be used. You can read more about our Privacy and Cookie Policy.


Durham Research Online
You are in:

On the helicity of open magnetic fields.

Prior, C.B. and Yeates, A.R. (2014) 'On the helicity of open magnetic fields.', Astrophysical journal., 787 (2). p. 100.

Abstract

We reconsider the topological interpretation of magnetic helicity for magnetic fields in open domains, and relate this to the relative helicity. Specifically, our domains stretch between two parallel planes, and each of these ends may be magnetically open. It is demonstrated that, while the magnetic helicity is gauge-dependent, its value in any gauge may be physically interpreted as the average winding number among all pairs of field lines with respect to some orthonormal frame field. In fact, the choice of gauge is equivalent to the choice of reference field in the relative helicity, meaning that the magnetic helicity is no less physically meaningful. We prove that a particular gauge always measures the winding with respect to a fixed frame, and propose that this is normally the best choice. For periodic fields, this choice is equivalent to measuring relative helicity with respect to a potential reference field. However, for aperiodic fields, we show that the potential field can be twisted. We prove by construction that there always exists a possible untwisted reference field.

Item Type:Article
Keywords:Magnetohydrodynamics (MHD), Methods: analytical, Methods: numerical, Sun: magnetic fields.
Full text:(VoR) Version of Record
Download PDF
(1750Kb)
Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1088/0004-637X/787/2/100
Publisher statement:© 2014. The American Astronomical Society. All rights reserved. Printed in the U.S.A.
Date accepted:10 April 2014
Date deposited:13 May 2014
Date of first online publication:07 May 2014
Date first made open access:No date available

Save or Share this output

Export:
Export
Look up in GoogleScholar