Abstract
Abstract. We present numerical results of 3-D MHD model of a dipole active region field containing a loop with a higher density than its surroundings. We study different ways of excitation of vertical kink oscillations by velocity perturbation: as an initial condition, and as an impulsive excitation with a pulse of a given position, duration, and amplitude. These properties are varied in the parametric studies. We find that the amplitude of vertical kink oscillations is significantly amplified in comparison to horizontal kink oscillations for exciters located centrally (symmetrically) below the loop, but not if the exciter is located a significant distance to the side of the loop. This explains why the pure vertical kink mode is so rarely observed in comparison to the horizontally polarized one. We discuss the role of curved magnetic field lines and the pulse overlapping at one of the loop's footpoints in 3-D active regions (AR's) on the excitation and the damping of slow standing waves. We find that footpoint excitation becomes more efficient in 3-D curved loops than in 2-D curved arcades and that slow waves can be excited within an interval of time that is comparable to the observed one wave-period due to the combined effect of the pulse inside and outside the loop. Additionally, we study the effect of AR topology on the excitation and trapping of loop oscillations. We find that a perturbation acting directly on a single loop excites oscillations, but results in an increased leakage compared to excitation of oscillations in an AR field by an external source.
Highlights
Observations with recent instruments such as SUMER onboard SOHO and TRACE in EUV wavelength resulted in the detection of various oscillations in solar coronal loops
Wang et al (2008) reconsidered oscillations described by Aschwanden et al (2002) and found that out of three oscillations previously identified as fundamental horizontal mode oscillations, two cases appeared to be fundamental vertical mode oscillations, and one case appeared to be a combination of the fundamental vertical and horizontal modes, while in three cases it was not possible to clearly distinguish between the fundamental mode and the second harmonic of the horizontal oscillation
We model coronal loop oscillations in an active region by means of 3-D MHD simulations
Summary
Observations with recent instruments such as SUMER onboard SOHO and TRACE in EUV wavelength resulted in the detection of various oscillations in solar coronal loops. Selwa et al (2005a) showed that pulses close to a footpoint excite the fundamental mode of the slow standing wave, while pulses close to the apex excite the second harmonic. These authors studied the influence of the pulse and loop parameters on the excitation and attenuation of slow standing waves. These slow modes are in the two entwined flux tubes created during the kink instability This excitation mechanism leads to fundamental standing mode after ∼2 wave-periods, so this model still does not fully explain the observations.
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