Detection of three periodicities in a single oscillating coronal loop

Doorsselaere, Tom Van; Birtill, David; Evans, G. R.

doi:10.1051/0004-6361/200912753

Cited by 34 publications

(17 citation statements)

References 30 publications

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“…The BCS oscillations have periods and damping times consistent with those for transverse loop oscillations (TLOs). Transverse oscillation periods longer than 10 min have been observed (Hori et al 2005;De Moortel & Brady 2007;Van Doorsselaere et al 2009;Verwichte et al 2009Verwichte et al , 2010, which puts them in the range of those periods observed with SUMER. Tothova et al (2011) detected in combined TRACE and SUMER observations the copresence of slow and transverse standing modes, which manifested themselves as oscillations in Doppler velocity in an emission line sensitive to hot plasma of 6 MK.…”

Section: Introductionmentioning

confidence: 70%

“…In particular, the density stratification inside coronal loops is related to the ratio of the fundamental period (P 1 ) to the period of the second harmonic (P 2 ). Another observation of higher order harmonics in TLOs was made by De Moortel & Brady (2007) for which a repeat analysis was conducted by Van Doorsselaere et al (2009). This spatially resolved TRACE observation allowed three periodicities to be detected (which were identified as the fundamental mode and both the first and second harmonics).…”

Section: Introductionmentioning

confidence: 99%

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First observation of a transverse vertical oscillation during the formation of a hot post-flare loop

White

Verwichte

Foullon

2012

A&A

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Aims. We report and analyse the first observation of a transverse oscillation in a hot coronal loop with the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO), following a linked coronal-flare mass-ejection event on the 3 November 2010. The oscillating coronal loop is observed off the east solar limb and exclusively in the 131 Å and 94 Å bandpasses, indicating a loop plasma of temperature in the range of 9-11 MK. Furthermore, the loop is not observed to cool into the other AIA channels, but just disappears from all bandpasses at the end of the oscillation. Methods. A time series analysis of the loop oscillation is conducted by taking several cuts at different positions along the loop, estimating the transverse displacements over time for two strands in the loop and fitting those with a damped cosine curve. Intensity time variations, both along the loop and for a series of cut cross-sections, are investigated. Using a three-dimensional loop geometry obtained from a comparison of STEREO-B/EUVI and AIA images, we model different modes of transverse oscillations in the uniformly filled loop. Results. Our time series analysis reveals a period of 302 ± 14 s (291 ± 9 s) and a damping time of 306 ± 43 s (487 ± 125 s) for the first (second) loop strand. A spatial phase shift along the loop of approximately 180 • suggests that we observe a higher order harmonic. Intensity oscillations are consistent with an interpretation in terms of a vertically polarised mode. Our forward modelling suggests that the loop oscillates as either a second or third order harmonic of this mode. Conclusions. This is the first observation of a transverse loop oscillation observed exclusively in the hot coronal lines. The loop oscillation is vertically polarised and is dominated by a higher order harmonic mode. We conclude that the excitation mechanism of this 5 min period oscillation is directly connected with the reconnection processes that form the post flare loop, which differs from the blast wave excitation mechanism often proposed as the cause of cooler transverse loop oscillations.

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Section: Introductionmentioning

confidence: 70%

Section: Introductionmentioning

confidence: 99%

First observation of a transverse vertical oscillation during the formation of a hot post-flare loop

White

Verwichte

Foullon

2012

A&A

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“…1, one may deduce that except for one all observations have τ/P ≥ 1. (There is one observation with a smaller quality factor, but the damping rate has a high uncertainty, Van Doorsselaere et al 2009.) However, an estimate of (τ/P) min based upon the observed lower limit in τ/P relies on only a few measurements.…”

Section: The Quality-factor Probability Density Distributionmentioning

confidence: 99%

Statistical seismology of transverse waves in the solar corona

Verwichte

Doorsselaere

White

et al. 2013

A&A

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Context. Observations show that transverse oscillations commonly occur in solar coronal loops. The rapid damping of these waves has been attributed to resonant absorption. The oscillation characteristics carries information of the structuring of the corona. However, self-consistent seismological methods that extract information from individual oscillations are limited because there are fewer observables than unknown parameters in the model, and the problem is underdetermined. Furthermore, it has been shown that one-to-one comparisons of the observed scaling of period and damping times with wave damping theories are misleading. Aims. We aim to investigate whether seismological information can be gained from the observed scaling laws in a statistical sense. Methods. A statistical approach is used whereby scaling laws are produced by forward modelling using distributions of values for key loop cross-sectional structuring parameters. We study two types of observations: 1) transverse loops oscillations as seen mainly with TRACE and SDO and 2) running transverse waves seen with the Coronal Multichannel Polarimeter (CoMP). Results. We demonstrate that the observed period-damping time scaling law does provide information about the physical damping mechanism, if observations are collected from as wide range of periods as possible and a comparison with theory is performed in a statistical sense. The distribution of the ratio of damping time over period, i.e. the quality factor, has been derived analytically and fitted to the observations. A minimum value for the quality factor of 0.65 has been found. From this, a constraint linking the ranges of possible values for the density contrast and inhomogeneity layer thickness is obtained for transverse loop oscillations. If the layer thickness is not constrained, then the density contrast is at most equal to 3. For transverse waves seen by CoMP, it is found that the ratio of maximum to minimum values for these two parameters has to be less than 2.06; i.e., the sampled values for the layer thickness and Alfvén travel time come from a relatively narrow distribution. Conclusions. Now that more and more transverse loop oscillations have been analysed, a statistical approach to coronal seismology becomes possible. Using the observed data cloud, we have found restrictions to the loop's density contrast and inhomogeneity layer thickness. Surprisingly, for running waves, narrow distributions for loop parameters have been found.

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“…Fortunately, there have been some signatures of overtones in coronal loop standing kink waves detected in TRACE data (see e.g. Verwichte et al 2004;De Moortel & Brady 2007;Van Doorsselaere et al 2009). For a particularly clear example of the first overtone damping before the fundamental mode, that could be explained by resonant absorption attenuating the higher harmonic faster, see the Morlet wavelet transform in Fig.…”

Section: Inhomogeneous Magnetic Cylindermentioning

confidence: 99%

Selective spatial damping of propagating kink waves due to resonant absorption

Terradas

Goossens

Verth

2010

A&A

126

143

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Context. There is observational evidence of propagating kink waves driven by photospheric motions. These disturbances, interpreted as kink magnetohydrodynamic (MHD) waves are attenuated as they propagate upwards in the solar corona. Aims. We show that resonant absorption provides a simple explanation to the spatial damping of these waves. Methods. Kink MHD waves are studied using a cylindrical model of solar magnetic flux tubes, which includes a non-uniform layer at the tube boundary. Assuming that the frequency is real and the longitudinal wavenumber complex, the damping length and damping per wavelength produced by resonant absorption are analytically calculated in the thin tube (TT) approximation, valid for coronal waves. This assumption is relaxed in the case of chromospheric tube waves and filament thread waves. Results. The damping length of propagating kink waves due to resonant absorption is a monotonically decreasing function of frequency. For kink waves with low frequencies, the damping length is exactly inversely proportional to frequency, and we denote this as the TGV relation. When moving to high frequencies, the TGV relation continues to be an exceptionally good approximation of the actual dependency of the damping length on frequency. This dependency means that resonant absorption is selective as it favours lowfrequency waves and can efficiently remove high-frequency waves from a broad band spectrum of kink waves. The efficiency of the damping due to resonant absorption depends on the properties of the equilibrium model, in particular on the width of the non-uniform layer and the steepness of the variation in the local Alfvén speed. Conclusions. Resonant absorption is an effective mechanism for the spatial damping of propagating kink waves. It is selective because the damping length is inversely proportional to frequency so that the damping becomes more severe with increasing frequency. This means that radial inhomogeneity can cause solar waveguides to be a natural low-pass filter for broadband disturbances. Kink wave trains travelling along, e.g., coronal loops, will therefore have a greater proportion of the high-frequency components dissipated lower down in the atmosphere. This could have important consequences for the spatial distribution of wave heating in the solar atmosphere.

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Detection of three periodicities in a single oscillating coronal loop

Cited by 34 publications

References 30 publications

First observation of a transverse vertical oscillation during the formation of a hot post-flare loop

First observation of a transverse vertical oscillation during the formation of a hot post-flare loop

Statistical seismology of transverse waves in the solar corona

Selective spatial damping of propagating kink waves due to resonant absorption

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