عنوان مجله
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MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
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چکیده
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There is ample evidence of twisted magnetic structures in the solar corona. This motivates
us to consider the magnetic twist as the cause of Alfv´en frequency continuum in coronal
loops, which can support the resonant absorption as a rapid damping mechanism for the
observed coronal kink magnetohydrodynamic (MHD) oscillations. We model a coronal loop
with a straight cylindrical magnetic flux tube, which has constant but different densities in
the interior and exterior regions. The magnetic field is assumed to be constant and aligned
with the cylinder axis everywhere except for a thin layer near the boundary of the flux tube,
which has an additional small magnetic field twist. Then, we investigate a number of possible
instabilities that may arise in our model. In the thin tube thin boundary approximation, we
derive the dispersion relation and solve it analytically to obtain the frequencies and damping
rates of the fundamental (l = 1) and first/second overtone (l = 2, 3) kink (m = 1) MHD
modes. We conclude that the resonant absorption by the magnetic twist can justify the rapid
damping of kink MHD waves observed in coronal loops. Furthermore, the magnetic twist in
the inhomogeneous layer can cause deviations from P1/P2 = 2 and P1/P3 = 3, which are
comparable with the observations.
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