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Surface currents on models of force-free solar magnetic flux tubes

Published online by Cambridge University Press:  13 March 2009

D. B. Melrose
Affiliation:
Research Centre for Theoretical Astrophysics, University of Sydney, NSW 2006, Australia
Jennifer Nicholls
Affiliation:
Research Centre for Theoretical Astrophysics, University of Sydney, NSW 2006, Australia
N. G. Broderick
Affiliation:
Research Centre for Theoretical Astrophysics, University of Sydney, NSW 2006, Australia

Abstract

A model of a cylindrically symmetric, force-free magnetic field consisting of a sequence of concentric layers with piecewise-constant α is used to construct models of the surface currents on isolated, force-free magnetic flux tubes. Two boundary conditions are considered: a current-neutralized flux tube (Bφ = 0, Bz φ 0, Bz ≠ O at r > r0), and an isolated current-carrying flux tube (Bφ0, Bz = 0 at r > r0). A single-a model that is current-neutralized is a reverse-field pinch, and is unacceptable as a model for a solar flux tube. Examples of two-α models for a current-neutralized flux tube are presented. The models of the surface currents satisfying either boundary condition are shown to simplify considerably when the surface layer is thin. A model consisting of several layers, with piecewise-constant α, may be used to find an approximate solution for a force-free flux tube with an arbitrarily specified current profile.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1994

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