EDP Sciences
Free access
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

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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