The P1/P2 period ratio for kink oscillations of an asymmetrical coronal loop

Orza, B.; Ballai, I.

doi:10.1002/asna.201211967

Cited by 8 publications

(7 citation statements)

References 49 publications

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“…Theoretically, the ratios of the fundamental kink mode period P (1) kink to the n-th parallel harmonic period, P (1) kink /(nP (n) kink ), have been shown to depend on the wave dispersion, i.e., the effects of finite k z , gravitational stratification, axial and perpendicular density structuring, loop cross-sectional ellipticity and geometry, and the axial magnetic field non-uniformity due to field expansion (e.g., Andries et al 2009b, and references therein). With regards to the density non-uniformity, this also depends upon the loop's temperature, curvature, inclination, etc., that affect the density scale-height and thus the harmonic period ratios (Orza et al 2012;Orza and Ballai 2013). For example, Ruderman et al (2016) showed that the period ratio P (1) kink /(2P (2) kink is lower or greater than unity when the kink speed increases or decreases with height, respectively.…”

Section: Theoretical Modelling Of the Period Ratiomentioning

confidence: 99%

Kink Oscillations of Coronal Loops

et al. 2021

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Kink oscillations of coronal loops, i.e., standing kink waves, is one of the most studied dynamic phenomena in the solar corona. The oscillations are excited by impulsive energy releases, such as low coronal eruptions. Typical periods of the oscillations are from a few to several minutes, and are found to increase linearly with the increase in the major radius of the oscillating loops. It clearly demonstrates that kink oscillations are natural modes of the loops, and can be described as standing fast magnetoacoustic waves with the wavelength determined by the length of the loop. Kink oscillations are observed in two different regimes. In the rapidly decaying regime, the apparent displacement amplitude reaches several minor radii of the loop. The damping time which is about several oscillation periods decreases with the increase in the oscillation amplitude, suggesting a nonlinear nature of the damping. In the decayless regime, the amplitudes are smaller than a minor radius, and the driver is still debated. The review summarises major findings obtained during the last decade, and covers both observational and theoretical results. Observational results include creation and analysis of comprehensive catalogues of the oscillation events, and detection of kink oscillations with imaging and spectral instruments in the EUV and microwave bands. Theoretical results include various approaches to modelling in terms of the magnetohydrodynamic wave theory. Properties of kink oscillations are found to depend on parameters of the oscillating loop, such as the magnetic twist, stratification, steady flows, temperature variations and so on, which make kink oscillations a natural probe of these parameters by the method of magnetohydrodynamic seismology.

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Section: Theoretical Modelling Of the Period Ratiomentioning

confidence: 99%

Kink Oscillations of Coronal Loops

et al. 2021

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“…However, since the loop length varies in their model (see page 3 in Orza & Ballai 2013), the difference between the lengths and also the longitudinal density slopes of the two sides of the loop can reach the values much greater than those of our model. For instance, in the model of Orza & Ballai (2013) for α = 0.6, the loops length changes by 21% in comparison with a semi-circular loop, and the length difference between the two sided is 46.7% of the loop length. Accordingly it shows that a large degree of asymmetry is needed in the coronal loops to affect the period ratio by a few percents.…”

Section: Asymmetric Loopmentioning

confidence: 99%

“…(2010) have made investigations in order to interpret the nature of and the mechanisms behind the asymmetric spectra of transition region or coronal medium structures. Orza & Ballai (2013) attributed the asymmetrical nature of a coronal loop to its shape and studied MHD oscillations of asymmetric coronal loops in various degrees of asymmetricity. Their results indicated that, in the presence of longitudinal stratification of mass density, when the temperature is the same inside and outside the loop, the asymmetry can alter the kink wave period ratio P 1 /P 2 by 5−8%.…”

Section: Introductionmentioning

confidence: 99%

Resonant Absorption of Kink MHD Waves in Inclined and Asymmetric Coronal Loops

Amiri,

Karami,

Ebrahimi

2021

Preprint

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This paper separately evaluates the effects of inclination and asymmetry of solar coronal loops on the resonant absorption of kink magnetohydrodynamic (MHD) oscillations. We modelled a typical coronal loop by a straight and axisymmetric cylindrical magnetic flux tube filled with cold plasma. We solved the dispersion relation numerically for different values of the longitudinal mass density stratification. We show that, in inclined and asymmetric loops, the frequencies and their corresponding damping rates of the fundamental and firstovertone modes of kink oscillations are smaller in comparison with semi-circular uninclined loops with the same lengths. The results also indicate that, the period ratio P 1 /P 2 , increases with increasing the inclination of the loop, but it decreases less than 2% while imposing the asymmetry to each loop side, up to 9.66% of the loop length. The ratio of each mode frequency to its corresponding damping rate remain unchanged approximately while the inclination or the asymmetry imposed. Hence, we conclude that these ratios are reliable for inferring the physical parameters of coronal loops and coronal medium, regardless of the loop shape or the state of its inclination. In addition, in contrast with the effect of asymmetry which is not significant on the period ratio P 1 /P 2 , when an observed oscillating loop has a smaller apex height, the state of its inclination is an important factor that should be considered, especially when the period ratio P 1 /P 2 , is taken into consideration for coronal seismology.

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“…Ruderman (2003) studied the period of oscillation and resonant damping of coronal loops with elliptic cross-sections. Morton & Erdélyi (2009) demonstrated curvature of the loop axis, with an elliptic shape, has a small effect on the period ratio, while Orza & Ballai (2013) showed coronal loops being asymmetrical also has a small effect on the ratio. Chen et al (2014) studied the effect of steady siphon flows and found that it significantly reduces the P 1 {nP n ratio.…”

Section: Introductionmentioning

confidence: 97%

Spatially resolved observation of the fundamental and second harmonic standing kink modes using SDO/AIA

Pascoe

Goddard

Nakariakov

2016

A&A

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Aims. We consider a coronal loop kink oscillation observed by the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO) which demonstrates two strong spectral components. The period of the lower frequency component being approximately twice that of the shorter frequency component suggests the presence of harmonics. Methods. We examine the presence of two longitudinal harmonics by investigating the spatial dependence of the loop oscillation. The time-dependent displacement of the loop is measured at 15 locations along the loop axis. For each position the detrended displacement is fitted as the sum of two damped sinusoids, having periods P 1 and P 2 , and a damping time τ. The shorter period component exhibits anti-phase oscillations in the loop legs. Results. We interpret the observation in terms of the first (global or fundamental) and second longitudinal harmonics of the standing kink mode. The strong excitation of the second harmonic appears connected to the preceding coronal mass ejection (CME) which displaced one of the loop legs. The oscillation parameters found are P 1 " 5.00˘0.62 minutes, P 2 " 2.20˘0.23 minutes, P 1 {2P 2 " 1.15˘0.22, and τ{P " 3.35˘1.45.

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The P₁/P₂ period ratio for kink oscillations of an asymmetrical coronal loop

Cited by 8 publications

References 49 publications

Kink Oscillations of Coronal Loops

Kink Oscillations of Coronal Loops

Resonant Absorption of Kink MHD Waves in Inclined and Asymmetric Coronal Loops

Spatially resolved observation of the fundamental and second harmonic standing kink modes using SDO/AIA

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