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The role of active region topology on excitation, trapping and damping of coronal loop oscillations View all abstracts by submitter

Mag Selwa   Submitted: 2009-12-01 04:04

We investigate the role of magnetic field topology on dense coronal loop oscillation by the means of 3D MHD numerical simulations of two models of idealized active regions (AR's). The first model of AR is initialized as a straight cylinder surrounded by the fieldlines of the same length and orientation. The second model consists of a potential dipole magnetic configuration and contains a loop with a higher density than its surroundings. Dipole fieldlines have position dependent length and orientation in contrary to straight ones. We study different ways of excitation of transverse loop oscillations by an external pulse and by a nearly eigenmode excitation implemented inside the loop. We find that perturbation acting directly on a single loop excites oscillations both in cylindrical and dipole loop. However, the leakage of the wave energy is larger in a curved loop compared to straight loop. External excitation of the whole AR is efficient in the excitation of oscillation in the straight field configuration, but results in less efficient excitation in the case of dipole field. We show that excitation of collective motion of straight fieldlines having the same wave-periods and planes of the oscillations requires much less energy than excitation of dipole fieldlines having position-dependent orientation and wave-periods and being excited individually, not having a collective mode of oscillation. We conclude that coherent motion of straight fieldlines is one of the factors that decrease the energy leakage from an oscillating loop, while individual motions of dipole fieldlines require more energy from the source to produce the loop oscillations, and also lead to higher damping rate compared to the straight field case. We discuss TRACE observations of coronal loop oscillations in view of our theoretical findings. We show several examples of time signatures of transversal loop oscillations observed by TRACE that agree with numerical simulations of externally excited oscillations.

Authors: M. Selwa, L. Ofman
Projects: None

Publication Status: Astrophysical Journal, submitted
Last Modified: 2010-01-22 06:17
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