Issue |
A&A
Volume 413, Number 3, January III 2004
|
|
---|---|---|
Page(s) | L27 - L30 | |
Section | Letters | |
DOI | https://doi.org/10.1051/0004-6361:20031691 | |
Published online | 07 January 2004 |
Letter to the Editor
Ideal kink instability of a magnetic loop equilibrium
1
Astrophysikalisches Institut Potsdam, 14482 Potsdam, Germany
2
School of Mathematics and Statistics, University of St Andrews, St Andrews, Fife KY16 9SS, UK
3
Theoretische Physik IV, Ruhr-Universität Bochum, 44780 Bochum, Germany
Corresponding author: T. Török, ttoeroek@aip.de
Received:
25
September
2003
Accepted:
3
November
2003
The force-free coronal loop model by [CITE] is found
to be unstable with respect to the ideal kink mode,
which suggests this instability as a mechanism for the initiation of flares.
The long-wavelength () mode grows for average
twists
(at a loop aspect ratio of ≈5).
The threshold of instability increases with increasing
major loop radius, primarily because the aspect ratio then also increases.
Numerically obtained equilibria at subcritical twist are very close to the
approximate analytical equilibrium; they do not show indications of
sigmoidal shape.
The growth of kink perturbations is eventually slowed down by the surrounding
potential field, which varies only slowly with radius in the model. With
this field
a global eruption is not obtained in the ideal MHD limit. Kink
perturbations with a rising loop apex lead to the
formation of a vertical current
sheet below the apex, which does not occur
in the cylindrical approximation.
Key words: instabilities / magnetic fields / MHD / Sun: activity / Sun: corona / stars: coronae
© ESO, 2004
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