Impulsively Generated Wave Trains in a Solar Coronal Loop

Jelínek, Petr; Karlický, M.

doi:10.1109/tps.2010.2052371

Cited by 14 publications

(7 citation statements)

References 28 publications

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“…In particular, the numerical studies by Nakariakov et al (2004) and Shestov et al (2015) showed that the period and amplitude modulations in the wave trains transform into tadpole-shaped Morlet spectra. This spectral feature was actually seen in both radio (e.g., Jelinek & Karlicky 2010;Karlický et al 2013) and optical measurements (e.g., Katsiyannis et al 2003;Samanta et al 2016). …”

Section: Introductionmentioning

confidence: 68%

Impulsively Generated Sausage Waves in Coronal Tubes With Transversally Continuous Structuring

Chen

et al. 2016

ApJ

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The frequency dependence of the longitudinal group speeds of trapped sausage waves plays an important role in determining impulsively generated wave trains, which have often been invoked to account for quasi-periodic signals in coronal loops. We examine how the group speeds (v gr ) depend on angular frequency (ω) for sausage modes in pressureless coronal tubes with continuous transverse density distributions by solving the dispersion relation pertinent to the case where the density inhomogeneity of arbitrary form takes place in a transition layer of arbitrary thickness. We find that in addition to the transverse lengthscale l and density contrast ρ i /ρ e , the group speed behavior depends also on the detailed form of the density inhomogeneity. For parabolic profiles, v gr always decreases with ω first before increasing again, as happens for the much studied top-hat profiles. For linear profiles, however, the behavior of the ω − v gr curves is more complex. When ρ i /ρ e 6, the curves become monotonical for large values of l. On the other hand, for higher density contrasts, a local maximum v in particular, is reflected in the temporal evolution and Morlet spectra of impulsively generated wave trains. We conclude that the observed quasi-periodic wave trains not only can be employed to probe such key parameters as density contrasts and profile steepness, but also have the potential to discriminate between the unknown forms of the transverse density distribution.

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Section: Introductionmentioning

confidence: 68%

Impulsively Generated Sausage Waves in Coronal Tubes With Transversally Continuous Structuring

Chen

et al. 2016

ApJ

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“…Using a two-dimensional (2D) MHD model with the Harris current sheet, they concluded that these wavelet tadpoles indicate the fast magnetoacoustic waves propagating in the reconnection plasma outflows. These studies were supported by numerical simulations made by Jelínek & Karlický (2010, where they compared the evolution of the fast magnetoacoustic waves in a dense slab and Harris current sheet depending on the plasma beta parameter and width of the waveguide. They found that an increase in the distance between the initial perturbation and the detection point increases the length of the tadpole tail.…”

Section: Introductionmentioning

confidence: 87%

Magnetoacoustic Waves Propagating Along a Dense Slab and Harris Current Sheet and Their Wavelet Spectra

Mészárosová

Karlický

Jelínek

et al. 2014

ApJ

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Currently, there is a common endeavor to detect magnetoacoustic waves in solar flares. This paper contributes to this topic using an approach of numerical simulations. We studied a spatial and temporal evolution of impulsively generated fast and slow magnetoacoustic waves propagating along the dense slab and Harris current sheet using two-dimensional magnetohydrodynamic numerical models. Wave signals computed in numerical models were used for computations of the temporal and spatial wavelet spectra for their possible comparison with those obtained from observations. It is shown that these wavelet spectra allow us to estimate basic parameters of waveguides and perturbations. It was found that the wavelet spectra of waves in the dense slab and current sheet differ in additional wavelet components that appear in association with the main tadpole structure. These additional components are new details in the wavelet spectrum of the signal. While in the dense slab this additional component is always delayed after the tadpole head, in the current sheet this component always precedes the tadpole head. It could help distinguish a type of the waveguide in observed data. We present a technique based on wavelets that separates wave structures according to their spatial scales. This technique shows not only how to separate the magnetoacoustic waves and waveguide structure in observed data, where the waveguide structure is not known, but also how propagating magnetoacoustic waves would appear in observations with limited spatial resolutions. The possibilities detecting these waves in observed data are mentioned.

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“…In particular, the numerical studies by Nakariakov et al (2004) and Shestov et al (2015) showed that the period and amplitude modulations in the wave trains transform into Morlet spectra characterized by a narrow tail followed by a broad head. Given their shape, these spectra are called "crazy tadpoles", and were indeed found in both radio (e.g., Jelinek & Karlicky 2010;Karlický et al 2013) and optical measurements (e.g., Katsiyannis et al 2003;Samanta et al 2016). If the measured short-period signals can be interpreted this way, then their temporal and wavelet features can be exploited to yield such key information as the internal Alfvén speed, density contrast between loops and their surroundings, as well as the location of the impulsive source (e.g., Roberts et al 1984;Roberts 2008).…”

Section: Introductionmentioning

confidence: 98%

Impulsively Generated Wave Trains in Coronal Structures. I. Effects of Transverse Structuring on Sausage Waves in Pressureless Tubes

Chen

et al. 2017

ApJ

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The behavior of the axial group speeds of trapped sausage modes plays an important role in determining impulsively generated wave trains, which have often been invoked to account for quasi-periodic signals with quasi-periods of order seconds in a considerable number of coronal structures. We conduct a comprehensive eigenmode analysis, both analytically and numerically, on the dispersive properties of sausage modes in pressureless tubes with three families of continuous radial density profiles. We find a rich variety of the dependence on the axial wavenumber k of the axial group speed v gr . Depending on the density contrast and profile steepness as well as on the detailed profile description, the v gr − k curves either possess or do not possess cutoff wavenumbers, and they can behave in either a monotonical or non-monotonical manner. With time-dependent simulations, we further show that this rich variety of the group speed characteristics heavily influences the temporal evolution and Morlet spectra of impulsively -2 -generated wave trains. In particular, the Morlet spectra can look substantially different from "crazy tadpoles" found for the much-studied discontinuous density profiles. We conclude that it is necessary to re-examine available high-cadence data to look for the rich set of temporal and spectral features, which can be employed to discriminate between the unknown forms of the density distributions transverse to coronal structures.

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Impulsively Generated Wave Trains in a Solar Coronal Loop

Cited by 14 publications

References 28 publications

Impulsively Generated Sausage Waves in Coronal Tubes With Transversally Continuous Structuring

Impulsively Generated Sausage Waves in Coronal Tubes With Transversally Continuous Structuring

Magnetoacoustic Waves Propagating Along a Dense Slab and Harris Current Sheet and Their Wavelet Spectra

Impulsively Generated Wave Trains in Coronal Structures. I. Effects of Transverse Structuring on Sausage Waves in Pressureless Tubes

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