The influence of the internal structuring of coronal loops on the properties of their damped transverse oscillations

Abstract

Context. The geometry and physical conditions in solar coronal loops are complicated and still not understood well. Recent highresolution observations obtained with TRACE indicate the existence of sub-resolution transverse structuring not accessible to direct observation. This ingredient has not yet been taken into account in the previous theoretical models used for the study of transversal coronal loop oscillations and of their damping due to resonant conversion of energy. Aims. This study aims to assess the effect of the possibly unresolved internal structure of a coronal loop on the properties of its transverse oscillations and on the efficiency of resonant absorption as a damping mechanism of these oscillations. Methods. The equilibrium configuration of a single coronal loop with internal density structuring is modelled by considering the loop as composed of two very close, parallel, identical coronal slabs in Cartesian geometry. The period of the oscillation and the damping time are computed for the resonantly damped fundamental kink mode. These quantities are then compared to those obtained for two models for a single equivalent slab without internal density structuring. Results. We find that the period and the damping time of a coronal loop with internal density structuring change by less than 15%, when compared to the same oscillatory properties of a single coronal loop with either the same density contrast or a single coronal loop with the same total mass. Conclusions. Therefore the internal density structuring of a coronal loop does not affect its oscillatory properties very much. However, the sub-resolution structuring of a coronal loop with different densities in its components or with different widths could vary these results.

Resonantly damped oscillations of two coronal loops

“…We also found that the damping rate due to resonant absorption is sufficiently reduced by the tube interaction. This difference between our results and those by Arregui et al (2007) is not very surprising. As we have already noted, the properties of kink oscillations of single slabs and tubes are quite different.…”

“…It is interesting to compare our results with those obtained by Arregui et al (2007). In their study of resonantly damped kink oscillations of the system of two parallel slabs these authors found that the properties of kink oscillations of this system and the damping time are practically the same as of a single slab with the equivalent parameters.…”

“…In this sense the properties of kink oscillations of a system of two tubes are quite different from those of two-slab system. While Arregui et al (2007) found only one fundamental eigenfrequency of kink oscillations, we found two of them and, as we know from the study by Luna et al (2008), actually there are four eigenfrequencies if the wave dispersion is taken into account. We also found that the damping rate due to resonant absorption is sufficiently reduced by the tube interaction.…”

“…It is therefore important to understand how the interaction of these neighbouring loops affects the oscillations and damping of coronal loops. To our knowledge Arregui et al (2007) were the first who investigated the influence of internal structuring of coronal loops on the properties of damped kink oscillations using Cartesian geometry. Resonantly damped oscillations of a system of two coronal loops, once again in Cartesian geometry, were studied by Arregui et al (2008).…”

Coupled Alfvén and Kink Oscillations in Coronal Loops

“…This result is consistent with that of Russell & Wright (2010) who demonstrated the persistence of resonant wave coupling in equilibria with a two-dimensional structure perpendicular to the background magnetic field. Arregui et al (2007b) also considered the effect of internal density structuring of a coronal loop on its oscillatory properties using a two-slab model. They found that the internal structure did not significantly affect the features of the resonantly damped fast mode oscillations (see also Goossens et al 2008).…”