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Numerical simulations of the conversion to Alfven waves in solar active regions


Khomenko Elena


Instituto de Astrofisica de Canarias


Solar and stellar modelling
Auteur(s) supplémentaire(s)Paul Cally
Institution(s) supplémentaire(s)School of Mathematical Sciences, Monash University, Australia


Conversion from fast to slow magneto-acoustic waves in
solar active regions is relatively well studied both from
analytical theories and numerical simulations. But no generalized
picture exists so far for conversion from magneto-acoustic to
Alfven waves in a three-dimensional situation. Motivated by the
recent study of the conversion to Alfven waves by Cally & Goossens
(2008), here we attack the problem by means of 2.5D numerical
simulations. In our experiment, an acoustic wave of a given
frequency and wavenumber is generated below the surface. The
magnetic field in the domain is assumed homogeneous and inclined.
The efficiency of the conversion to Alfven waves near the layer of
equal acoustic and Alfven speeds is measured calculating their
energy flux. The particular amplitude and phase relations between
the oscillations of magnetic field and velocity help us to
demonstrate that the waves produced after the transformation and
reaching upper atmosphere are indeed Alfven waves. We study the
dependence of the Alfven wave energy flux on the wave frequency,
wavenumber, magnetic field strength and orientation. We also investigate
the possible influence of the radiative relaxation of
oscillations on the conversion rate to Alfven waves.
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