Issue |
A&A
Volume 422, Number 3, August II 2004
|
|
---|---|---|
Page(s) | 1085 - 1091 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361:20040200 | |
Published online | 16 July 2004 |
Dynamics and heating of the magnetic network on the Sun
Efficiency of mode transformation
1
Indian Institut of Astrophysics, Bangalore-560034, India e-mail: hasan@iiap.res.in
2
Institut für Theoretische Astrophysik, Tiergartenstr. 15, 69121 Heidelberg, Germany e-mail: ulm@ita.uni-heidelberg.de
Received:
5
February
2004
Accepted:
20
April
2004
We aim to identify the physical processes which occur in the magnetic
network of the chromosphere and which contribute to its dynamics and
heating. Specifically, we study the propagation of transverse (kink)
MHD waves which are impulsively excited in flux tubes through
footpoint motions. When these waves travel upwards, they get
partially converted to longitudinal waves through nonlinear effects
(mode coupling). By solving the nonlinear, time-dependent MHD equations we find that significant longitudinal wave generation
occurs in the photosphere typically for Mach numbers as low as 0.2 and
that the onset of shock formation occurs at heights of about 600 km
above the photospheric base. We also investigate the compressional
heating due to longitudinal waves and the efficiency of mode
coupling for various values of the plasma β, that parameterises
the magnetic field strength in the network. We find that this
efficiency is maximum for field strengths corresponding to , when the kink and tube wave speeds are almost
identical. This can have interesting observational
implications. Furthermore, we find that even when the two speeds are
different, once shock formation occurs, the longitudinal and
transverse shocks exhibit strong mode coupling.
Key words: Sun: magnetic fields / Sun: oscillations / Sun: chromosphere
© ESO, 2004
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