Excitation of kink oscillations of coronal loops: statistical study

Zimovets, I. V.; Nakariakov, V. M.

doi:10.1051/0004-6361/201424960

Cited by 121 publications

(140 citation statements)

References 46 publications

Supporting

Mentioning

130

Contrasting

Order By: Relevance

“…Large-amplitude, rapidly decaying kink oscillations of coronal loops are usually excited by low coronal eruptive events that mechanically displace them from equilibrium (Zimovets & Nakariakov 2015). Small-amplitude undamped kink oscillations are observed continuously without any visible driver.…”

Section: Introductionmentioning

confidence: 99%

Undamped transverse oscillations of coronal loops as a self-oscillatory process

Nakariakov

Anfinogentov

Nisticò

et al. 2016

A&A

Self Cite

View full text Add to dashboard Cite

Context. Standing transverse oscillations of coronal loops are observed to operate in two regimes: rapidly decaying, large amplitude oscillations and undamped small amplitude oscillations. In the latter regime the damping should be compensated by energy supply, which allows the loop to perform almost monochromatic oscillations with almost constant amplitude and phase. Different loops oscillate with different periods. The oscillation amplitude does not show dependence on the loop length or the oscillation period. Aims. We aim to develop a low-dimensional model explaining the undamped kink oscillations as a self-oscillatory process caused by the effect of negative friction. The source of energy is an external quasi-steady flow, for example, supergranulation motions near the loop footpoints or external flows in the corona. Methods. We demonstrate that the interaction of a quasi-steady flow with a loop can be described by a Rayleigh oscillator equation that is a non-linear ordinary differential equation, with the damping and resonant terms determined empirically. Results. Small-amplitude self-oscillatory solutions to the Rayleigh oscillator equation are harmonic signals of constant amplitude, which is consistent with the observed properties of undamped kink oscillations. The period of self-oscillations is determined by the frequency of the kink mode. The damping by dissipation and mode conversion is compensated by the continuous energy deposition at the frequency of the natural oscillation. Conclusions. We propose that undamped kink oscillations of coronal loops may be caused by the interaction of the loops with quasi-steady flows, and hence are self-oscillations, which is analogous to producing a tune by moving a bow across a violin string.

show abstract

Section: Introductionmentioning

confidence: 99%

Undamped transverse oscillations of coronal loops as a self-oscillatory process

Nakariakov

Anfinogentov

Nisticò

et al. 2016

A&A

Self Cite

View full text Add to dashboard Cite

show abstract

“…High-resolution SDO data has also led to the discovery of low-amplitude decayless standing oscillations Anfinogentov et al 2013), which appear to be ubiquitous in active regions (Anfinogentov et al 2015). The excitation mechanism for these low-amplitude oscillations is not yet understood, while a recent statistical study by Zimovets & Nakariakov (2015) demonstrates that the high-amplitude decaying kink oscillations are more commonly excited by low-coronal eruptions rather than blast waves launched by flares. The selectivity of the excitation is therefore connected with direct interaction with the erupting plasma, rather than interaction with an external wave (e.g.…”

Section: Introductionmentioning

confidence: 99%

Coronal loop seismology using damping of standing kink oscillations by mode coupling

Pascoe

Goddard

Nisticò

et al. 2016

A&A

Self Cite

View full text Add to dashboard Cite

Context. Kink oscillations of solar coronal loops are frequently observed to be strongly damped. The damping can be explained by mode coupling on the condition that loops have a finite inhomogeneous layer between the higher density core and lower density background. The damping rate depends on the loop density contrast ratio and inhomogeneous layer width. Aims. The theoretical description for mode coupling of kink waves has been extended to include the initial Gaussian damping regime in addition to the exponential asymptotic state. Observation of these damping regimes would provide information about the structuring of the coronal loop and so provide a seismological tool. Methods. We consider three examples of standing kink oscillations observed by the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO) for which the general damping profile (Gaussian and exponential regimes) can be fitted. Determining the Gaussian and exponential damping times allows us to perform seismological inversions for the loop density contrast ratio and the inhomogeneous layer width normalised to the loop radius. The layer width and loop minor radius are found separately by comparing the observed loop intensity profile with forward modelling based on our seismological results. Results. The seismological method which allows the density contrast ratio and inhomogeneous layer width to be simultaneously determined from the kink mode damping profile has been applied to observational data for the first time. This allows the internal and external Alfvén speeds to be calculated, and estimates for the magnetic field strength can be dramatically improved using the given plasma density. Conclusions. The kink mode damping rate can be used as a powerful diagnostic tool to determine the coronal loop density profile. This information can be used for further calculations such as the magnetic field strength or phase mixing rate.

show abstract

“…standing kink or slow-mode waves. These waves can be directly or indirectly excited by an impulsive source associated with the flare or CME (e.g., Aschwanden et al 2002;Nakariakov et al 2004;Tsiklauri et al 2004;Selwa et al 2005;Selwa & Ofman 2010;Zimovets & Nakariakov 2015). QPPs have been detected at many wavelengths, from radio (e.g., Wright & Nelson 1987;Qin et al 1996;Grechnev et al 2003;Nakariakov et al 2003) to extreme ultraviolet (EUV) (e.g., Wang et al 2003), X-ray (e.g., Harrison 1987;Li & Gan 2008;Ning 2014), and gamma-ray ).…”

Section: Introductionmentioning

confidence: 99%

Comparison of Damped Oscillations in Solar and Stellar X-Ray Flares

Cho

Nakariakov

Kim

et al. 2016

ApJ

Self Cite

View full text Add to dashboard Cite

We explore the similarity and difference of the quasi-periodic pulsations (QPPs) observed in the decay phase of solar and stellar flares at X-rays. We identified 42 solar flares with pronounced QPPs, observed with the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) and 36 stellar flares with QPPs, observed with X-ray Multi Mirror Newton observatory (XMM-Newton). The Empirical Mode Decomposition (EMD) method and least-square fit by a damped sine function were applied to obtain the periods (P ) and damping times (τ ) of the QPPs. We found that (1) the periods and damping times of the stellar QPPs are 16.21±15.86 min and 27.21±28.73 min, while those of the solar QPPs are 0.90±0.56 and 1.53±1.10 min, respectively. (2) The ratio of the damping times to the periods (τ /P ) observed in the stellar QPPs (1.69±0.56) are statistically identical to those of solar QPPs (1.74±0.77). (3) The scalings of the QPP damping time with the period are well described by the power law in both solar and stellar cases. The power indices of the solar and stellar QPPs are 0.96±0.10 and 0.98±0.05, respectively. This scaling is consistent with the scalings found for standing slow magnetoacoustic and kink modes in solar coronal loops. Thus, we propose that the underlying mechanism responsible for the stellar QPPs is the natural magnetohydrodynamic oscillations in the flaring or adjacent coronal loops, as in the case of solar flares.

show abstract

Excitation of kink oscillations of coronal loops: statistical study

Cited by 121 publications

References 46 publications

Undamped transverse oscillations of coronal loops as a self-oscillatory process

Undamped transverse oscillations of coronal loops as a self-oscillatory process

Coronal loop seismology using damping of standing kink oscillations by mode coupling

Comparison of Damped Oscillations in Solar and Stellar X-Ray Flares

Contact Info

Product

Resources

About