Issue |
A&A
Volume 375, Number 1, August III 2001
|
|
---|---|---|
Page(s) | 264 - 274 | |
Section | Planets and planetary systems | |
DOI | https://doi.org/10.1051/0004-6361:20010869 | |
Published online | 15 August 2001 |
Nonlinear fast magnetosonic waves in solar coronal holes
1
Department of Environmental Physics, Technical University of Lublin, ul. Nadbystrzycka 40, 20-618 Lublin, Poland
2
Departament de Física, Universitat de les Illes Balears, 07071 Palma de Mallorca, Spain e-mail: ramon.oliver@uib.es, dfsjlb0@uib.es
Corresponding author: K. Marawski kamur@akropolis.pol.lublin.pl
Received:
2
March
2001
Accepted:
14
June
2001
A coronal hole is modeled as a slab of cold plasma threaded by a vertical,
uniform magnetic field. A periodic driver acting at the coronal base is
assumed to drive the velocity component normal to the equilibrium magnetic
field. Previous works indicate that, in the linear regime, only fast mode
perturbations propagate, since
Alfvén waves are excluded from the model and
the slow wave is absent in the cold plasma limit. However, in this
work, it is shown that nonlinear terms in the
magnetohydrodynamic (MHD) equations give rise to excitation of the velocity
component parallel to the equilibrium , with a lower amplitude than
the normal component.
Another consequence of nonlinearities is the generation of higher-frequency
Fourier modes, which can be detected by Fourier analyzing the velocity
variations
above the photosphere. The nature of the nonlinear interactions in the
MHD equations determines the frequency of those modes. These interactions
are quadratic in the case of the parallel component, while they are cubic
in the case of the normal component. Therefore, nonlinearly excited
frequencies
,
,
, … are present in
the parallel velocity, whereas frequencies
,
,
, … are present in the normal velocity, with
the driving frequency.
Key words: Sun: corona / Sun: magnetic fields / magnetohydrodynamics
© ESO, 2001
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