The Role of Active Region Topology in Excitation, Trapping, and Damping of Coronal Loop Oscillations

Details The Role of Active Region Topology in Excitation, Trapping, and Damping of Coronal Loop Oscillations The Role of Active Region Topology in Excitation, Trapping, and Damping of Coronal Loop Oscillations

May 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010apj...714..170s&link_type=abstract

The Astrophysical Journal, Volume 714, Issue 1, pp. 170-177 (2010).

Astronomy and Astrophysics

Astronomy

6

Sun: Corona, Sun: Oscillations

Scientific paper

We investigate the role of magnetic field topology in dense coronal loop oscillation by the means of three-dimensional magnetohydrodynamic numerical simulations of two models of idealized active regions (ARs). The first AR model is initialized as a straight cylinder surrounded by the field lines 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 field lines 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 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 loops. However, the leakage of the wave energy is larger in a curved loop compared to a 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 field lines having the same wave periods and planes of the oscillations requires much less energy than excitation of dipole field lines 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 field lines is one of the factors that decrease the energy leakage from an oscillating loop, while individual motions of dipole field lines 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 Transition Region and Coronal Explorer (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.

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