The thermal continuum in coronal loops: The influence of finite resistivity on the continuous spectrum |
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| Authors: | R C Ireland R A M Van Der Linden A W Hood M Goossens |
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| Institution: | (1) Department of Mathematical and Computational Sciences, University of St. Andrews, St. Andrews, KY16 9SS Fife, Scotland;(2) Centre for Plasma Astrophysics, Department of Mathematics, Katholieke Universiteit Leuven, 3001 Heverlee, Belgium |
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| Abstract: | The normal mode spectrum for the linearized MHD equations is investigated for a cylindrical equilibrium. This spectrum is examined for zero perpendicular thermal conduction, with both zero and non-zero scalar resistivity. Particular attention is paid to the continuous branches of this spectrum, or continuous spectra. For zero resistivity there are three types of continuous spectra present, namely the Alfvén, slow, and thermal continua. It is shown that when dissipation due to resistivity is included, the slow and Alfvén continua are removed and that the thermal continuum is shifted to a different position (where the shift is independent of the exact value of resistivity). The  old location of the thermal continuum is covered by a dense set of nearly singular discrete modes called a quasi-continuum. The quasi-continuum is investigated numerically, and the eigenfunctions are shown to have rapid spatial oscillating behaviour. These oscillations are confined to the most unstable part of the equilibrium based on the Field criterion, and may be the cause of fine structure in prominences. |
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