All Coronal Loops Are the Same: Evidence to the Contrary

Schmelz, J. T.; Nasraoui, K.; Richardson, V. L.; Hubbard, Peter; Nevels, C. R.; Beene, J. E.

doi:10.1086/431950

Cited by 25 publications

(28 citation statements)

References 18 publications

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“…Most of these previous models assume monolithic equilibrium configurations with uniform internal density in the direction transverse to field lines, which is an over-simplification of the real physical conditions in coronal loops. For instance, high-resolution observations suggest the existence of sub-resolution transverse structuring, not accessible to direct observation with our current capabilities (Schmelz et al 2005). This view has been challenged in some works (Aschwanden & Nightingale 2005;Aschwanden 2005), although it is supported in some others (e.g.…”

Section: Introductionmentioning

confidence: 86%

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

Arregui

Terradas

Oliver

et al. 2007

A&A

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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.

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Section: Introductionmentioning

confidence: 86%

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

Arregui

Terradas

Oliver

et al. 2007

A&A

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“…In the least, contamination from diffuse background and/or foreground emission is present, or the plasma is multithermal (e.g., Schmelz et al 2005;Schmelz & Martens 2006;Cirtain et al 2007;Schmelz et al 2007aSchmelz et al , 2008Aschwanden et al 2008;Schmelz et al 2009a;Terzo & Reale 2010;O'Dwyer et al 2010), or there is a contribution from low-intensity high-temperature component (e.g. Reale et al 2009a,b;Schmelz et al 2009b,c).…”

Section: Temperature Diagnostic Using Cifrmentioning

confidence: 99%

Is it possible to model observed active region coronal emission simultaneously in EUV and X-ray filters?

Dudík

Dzifčáková

Karlický

et al. 2011

A&A

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Aims. We investigate the possibility of modeling the active region coronal emission in the EUV and X-ray filters using one, universal, steady heating function, tied to the properties of the magnetic field. Methods. We employ a simple, static model to compute the temperature and density distributions in the active region corona. The model allows us to explore a wide range of parameters of the heating function. The predicted EUV and X-ray emission in the filters of EIT/SOHO and XRT/Hinode are calculated and compared with observations. Using the combined improved filter-ratio (CIFR) method, a temperature diagnostic is employed to compare the modeled temperature structure of the active region with the temperature structure derived from the observations. Results. The global properties of the observations are most closely matched for heating functions scaling as B 0.7−0.8 0 /L 0.5 0 that depend on the spatially variable heating scale-length. The modeled X-ray emission originates from locations where large heating scale-lengths are found. However, the majority of the loops observed in the 171 and 195 filters can be modeled only by loops with very short heating scale-lengths. These loops are known to be thermally unstable. We are unable to find a model that both matches the observations in all EUV and X-ray filters, and contains only stable loops. As a result, although our model with a steady heating function can explain some of the emission properties of the 171 and 195 loops, it cannot explain their observed lifetimes. Thus, the model does not lead to a self-consistent solution. The performance of the CIFR method is evaluated and we find that the diagnosed temperature can be approximated with a geometric mean of the emission-measure weighted and maximum temperature along the line of sight. Conclusions. We conclude that if one universal heating function exists, it should be at least partially time-dependent.

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“…Moreover it has also been suggested that the coronal magnetic loops are in fact collections of very thin magnetic ropes bundled together (e.g. Martens et al 2002;Schmelz et al 2003Schmelz et al , 2005Aschwanden 2005;Aschwanden & Nightingale 2005). It is therefore important to understand how the interaction of these neighbouring loops affects the oscillations and damping of coronal loops.…”

Section: Introductionmentioning

confidence: 99%

Resonantly damped oscillations of two coronal loops

Robertson

2010

A&A

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Transverse oscillations of coronal magnetic loops are routinely observed during the space missions. Since the first observation these oscillations were interpreted in terms of kink oscillations of magnetic tubes. Sometimes collective oscillations of two or more coronal loops are observed. This makes the development of theory of collective oscillations of a few parallel magnetic tubes desirable. Another reason for the development of this theory is that there are evidences that at least some coronal loops are not monolithic but consist of many thin magnetic threads. In this paper the linear theory of resonant damping of kink oscillations of two parallel magnetic tubes is developed. Two small parameters, the ratio of the distance between the tubes to the tube length and the ratio of thickness of regions with varying density to the tube radius, are used to obtain the asymptotic expression for the decrement. This expression is calculated explicitly in a particular case of two identical tubes. The dependence of damping time on the separation distance between the tubes and on the density contrast is investigated. In particular, we obtained that the interaction between the tubes reduces the efficiency of resonant absorption.

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All Coronal Loops Are the Same: Evidence to the Contrary

Cited by 25 publications

References 18 publications

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

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

Is it possible to model observed active region coronal emission simultaneously in EUV and X-ray filters?

Resonantly damped oscillations of two coronal loops

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