EDP Sciences
Free access
Volume 487, Number 3, September I 2008
Page(s) 1155 - 1161
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:200809960
Published online 01 July 2008

A&A 487, 1155-1161 (2008)
DOI: 10.1051/0004-6361:200809960

Anisotropic viscous dissipation in compressible magnetic X-points

I. J. D. Craig

Department of Mathematics, University of Waikato, PB 3105, Hamilton, New Zealand

Received 14 April 2008 / Accepted 20 June 2008

Context. Visco-resistive damping in line-tied magnetic X-points is examined.
Aims. The goal is to determine whether fast, Alfvénic energy dissipation is possible for X-point disturbances damped by the plasma resistivity and non-isotropic viscosity.
Methods. The response of X-points to planar and axial perturbations is explored numerically by solving the linearized compressible MHD equations in two and a half dimensions.
Results. It is demonstrated that fast dissipation is possible in the case of non-reconnective planar disturbances damped by anisotropic viscosity in weakly resistive plasmas. Although perturbations which change the initial X-point topology decay slowly at large times when viscous effects are dominant, there is an initial phase in which a significant fraction of the disturbance energy is removed on an Alfvénic timescale. The decay of incompressive axial field disturbances occurs by a different mechanism, however, that is always formally slow (i.e. dependent on the small viscous and resistive damping coefficients).
Conclusions. Computations suggest that fast, visco-resistive energy release in coronal plasmas is possible for compressive X-point disturbances. This result could have important implications for understanding rapid energy release in coronal active regions.

Key words: magnetohydrodynamics (MHD) -- Sun: flares -- Sun: magnetic fields -- Sun: corona -- plasmas

© ESO 2008