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Phase mixing of alfven waves in an open stratified atmosphere
Ineke De Moortel
(St Andrews)
Phase mixing was introduced by Heyvaerts and Priest (1983) as a
mechanism for heating the plasma in the open magnetic field regions
of coronal holes. Here the basic process is modified to include a
stratified atmosphere in which the density decreases with height and to
include a diverging magnetic field. We
present WKB solutions and
use a numerical code in the non-zero dissipation case to describe the
effect of stratification and divergence on phase mixing of Alfven waves.
It is shown that the decrease in density lengthens the
oscillation wavelengths and thereby reduces the generation of
transverse gradients. However, the divergence of the field lines shortens
the wavelengths and thereby enhances the generation of gradients.
Furthermore we found that in a stratified atmosphere the perturbed
magnetic field and velocity behave quite differently depending on whether
we consider resistivity or viscosity. Ohmic heating is spread out over a
greater height range in a stratified medium whereas viscous heating is not
strongly influenced by the stratification.
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