EDP Sciences
Free access
Issue
A&A
Volume 489, Number 3, October III 2008
Page(s) 1291 - 1295
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20078717
Published online 28 July 2008


A&A 489, 1291-1295 (2008)
DOI: 10.1051/0004-6361:20078717

Mixing of shear Alfven wave packets

N. Bian1 and D. Tsiklauri2

1  Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester, M60 1QD, UK
    e-mail: nbian@hotmail.com
2  Institute for Material Research, University of Salford, Greater Manchester, M5 4WT, UK

Received 21 September 2007 / Accepted 26 May 2008

Abstract
Aims. We consider the propagation of shear Alfven wave packets in inhomogeneous magnetic fields which is at the origin of their distortion regardless of any non-linear coupling. It is shown that this can be regarded as a mixing process and hence, standard phase mixing corresponds to the effect of an Alfvenic shear flow, while enhanced dissipation at a magnetic X-point corresponds to mixing by an Alfvenic strain flow.
Methods. The evolution of the wave field is supposed to result from the dynamics of a superposition of wave packets, and a kinetic equation for the wave energy is obtained following this eikonal (WKB) description.
Results. Since shear Alfven wave packets experience continuous shearing/straining, while transported by an inhomogeneous Alfvenic flow $\vec{V}_{\rm A}$, their mixing process in physical space is also a cascade of wave energy in k-space. The wave energy spectrum resulting from this linear mechanism of energy transfer is determined for the special case of waves propagating along chaotic magnetic field lines, the analog of a chaotic mixing process. The latter follows a k-1 power law in the energy conserving range in k space.


Key words: magnetohydrodynamics (MHD) -- waves -- magnetic fields



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