Issue |
A&A
Volume 489, Number 3, October III 2008
|
|
---|---|---|
Page(s) | 1291 - 1295 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361:20078717 | |
Published online | 28 July 2008 |
Mixing of shear Alfven wave packets
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 , 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
© ESO, 2008
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