Physics
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsh53a1071c&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #SH53A-1071
Physics
7509 Corona
Scientific paper
Magnetohydrodynamic (MHD) stability (kink and sausage modes) and damped oscillations of coronal loops are investigated. A coronal loop is treated as a thin toroidal flux rope with two stationary photospheric footpoints, carrying both toroidal and poloidal currents. The forces and the flux-rope dynamics are described within the framework of ideal MHD. The main features of the theory are (1) oscillatory motions are determined by the Lorentz force that acts on curved current-carrying plasma structures and (2) damping is caused by drag that provides the momentum coupling between the flux rope and the ambient coronal plasma. The oscillation is restricted to the vertical plane of the flux rope. The kink- and sausage-mode properties of the initial equilibrium flux rope are investigated. The initial flux rope is set into oscillation by a pulse of upflow of the ambient plasma. The theory is applied to oscillating loops observed by Transition Region and Coronal Explorer (TRACE). It is shown that the component of the ambient magnetic field parallel to the flux rope plays a key role in the stability and that the Lorentz force and drag with a reasonable value of the coupling coefficient (cd) and without anomalous dissipation are able to accurately account for the observed damped oscillations. The analysis shows that the variations in the observed intensity can be explained by the minor radial expansion and contraction. The values of the drag coefficient required to produce the observed damping times are in the range cd ≈~2 - - 5, consistent with a previous MHD simulation study and with values used to reproduce the observed trajectories of coronal mass ejections (CMEs). Work supported by ONR and NASA
Chen Jiahua
Schuck Peter W.
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