Relationship between wave processes in sunspots and quasi-periodic pulsations in active region flares

Сыч, Р. А.; Nakariakov, V. M.; Karlický, M.; Anfinogentov, Sergey

doi:10.1051/0004-6361/200912132

Cited by 144 publications

(119 citation statements)

References 27 publications

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“…This method yields the spatial distribution of the power, frequency, and phase of an oscillatory signal, and is intensively used in the study of sunspot oscillations (e.g., Sych et al 2009). …”

Section: Methodsmentioning

confidence: 99%

Multi-height observations of magnetoacoustic cut-off frequency in a sunspot atmosphere

Yuan

Сыч

Reznikova

et al. 2013

A&A

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Context. The cut-off frequency of magnetoacoustic gravity (MAG) waves could be decreased by the inclined magnetic field, and therefore, low-frequency waves could penetrate into the upper atmosphere. Aims. We observe the distribution of the cut-off frequency of compressive waves at various heights and reconstruct the magnetic field inclination, according to the MAG wave theory in a stratified atmosphere permeated by a uniform magnetic field. Methods. We analysed the emission intensity oscillations of sunspot AR11131 (08 Dec. 2010) observed at the 1700 Å, 1600 Å, and 304 Å bandpasses of the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO), and computed the narrow-band power maps with the pixelised wavelet filtering method. The distribution of the cut-off frequency was defined as the median contour in the azimuthally-averaged oscillation power. The magnetic field inclination was estimated with the local cut-off frequency according to the MAG wave theory in the low-β limit and was compared to the potential field extrapolation. Results. Shorter period oscillations dominate in the sunspot umbra, while longer period oscillations form an annular shape approximately concentric with the sunspot. Oscillations with longer periods are distributed further away from the sunspot centre. The 5 min oscillations appear to originate at or lower than the photosphere. The magnetic field inclinations determined with the cut-off frequency theory are about 30−40% larger than the values obtained by the potential field extrapolation. Conclusions. The oscillation power distribution in a sunspot atmosphere reflects its magnetic and thermal structure. The cut-off frequency could be used to probe the magnetic field inclination, however, other factors have to be included to fully understand this phenomenon. The existence of return magnetic flux at the outer penumbra was evidenced by the cut-off frequency distribution.

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Section: Methodsmentioning

confidence: 99%

Multi-height observations of magnetoacoustic cut-off frequency in a sunspot atmosphere

Yuan

Сыч

Reznikova

et al. 2013

A&A

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“…This feature suggests the likely association of the coronal propagating disturbances with chromospheric 3-min oscillations and the photospheric 5-min oscillations, respectively. Chromospheric 3-min oscillations were found to leak from sunspot umbrae to the corona (Shibasaki 2001;Sych et al 2009;Botha et al 2011). Photospheric 5-min oscillations in plage regions are apt to be wave-guided to the corona by inclined magnetic field lines (Bel & Leroy 1977), and could be associated with the leakage of global p-modes from the photosphere (De Pontieu et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Measuring the apparent phase speed of propagating EUV disturbances

Yuan

Nakariakov

2012

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Context. Propagating disturbances of the EUV emission intensity are commonly observed over a variety of coronal structures. Parameters of these disturbances, particularly the observed apparent (image-plane projected) propagation speed, are important tools for MHD coronal seismology. Aims. We design and test tools to reliably measure the apparent phase speed of propagating disturbances in imaging data sets. Methods. We designed cross-fitting technique (CFT), 2D coupled fitting (DCF) and best similarity match (BSM) to measure the apparent phase speed of propagating EUV disturbances in the running differences of time-distance plots (R) and background-removed and normalised time-distance plots (D).Results. The methods were applied to the analysis of quasi-periodic EUV disturbances propagating at a coronal fan-structure of active region NOAA11330 on 27 Oct. 2011, observed with the Atmospheric Imaging Assembly (AIA) on SDO in the 171 Å bandpass. The noise propagation in the AIA image processing was estimated, resulting in the preliminary estimation of the uncertainties in the AIA image flux. This information was used in measuring the apparent phase speed of the propagating disturbances with the CFT, DCF and BSM methods, which gave consistent results. The average projected speed is measured at 47.6 ± 0.6 km s −1 and 49.0 ± 0.7 km s −1 for R and D, with the corresponding periods at 179.7 ± 0.2 s and 179.7 ± 0.3 s, respectively. We analysed the effects of the lag time and the detrending time in the running difference processing and the background-removed plot, on the measurement of the speed, and found that they are fairly weak. Conclusions. The CFT, DCF and BSM methods are found to be reliable techniques for measuring the apparent (projected) phase speed. The samples of larger effective spatial length are more suitable for these methods. Time-distance plots with background removal and normalisation allow for more robust measurements, with little effect of the choice of the detrending time. Cross-fitting technique provides reliable measurements on good samples (e.g. samples with large effective detection length and recurring features). 2D coupled-fitting is found to be sensitive to the initial guess for parameters of the 2D fitting function. Thus DCF is only optimised in measuring one of the parameters (the phase speed in our application), while the period is poorly measured. Best similarity measure is robust for all types of samples and very tolerant to image pre-processing and regularisation (smoothing).

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“…However, the origin of these propagating, transverse oscillations remains a mystery, and these authors often note that the challenge remains to understand how and where these waves are generated in the solar atmosphere. Liu et al (2011) summarises possible generation mechanisms for these transverse motions, including an oscillating wake from a coronal mass ejection or periodic reconnection (see, e.g., Chen & Priest 2006;Sych et al 2009). The physical mechanism of oscillatory reconnection is another possible source of these transverse motions.…”

Section: Introductionmentioning

confidence: 99%

On the periodicity of oscillatory reconnection

McLaughlin¹,

Thurgood²,

MacTaggart³

2012

A&A

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Context. Oscillatory reconnection is a time-dependent magnetic reconnection mechanism that naturally produces periodic outputs from aperiodic drivers. Aims. This paper aims to quantify and measure the periodic nature of oscillatory reconnection for the first time. Methods. We solve the compressible, resistive, nonlinear magnetohydrodynamics (MHD) equations using 2.5D numerical simulations. Results. We identify two distinct periodic regimes: the impulsive and stationary phases. In the impulsive phase, we find the greater the amplitude of the initial velocity driver, the longer the resultant current sheet and the earlier its formation. In the stationary phase, we find that the oscillations are exponentially decaying and for driving amplitudes 6.3−126.2 km s −1 , we measure stationary-phase periods in the range 56.3−78.9 s, i.e. these are high frequency (0.01−0.02 Hz) oscillations. In both phases, we find that the greater the amplitude of the initial velocity driver, the shorter the resultant period, but note that different physical processes and periods are associated with both phases. Conclusions. We conclude that the oscillatory reconnection mechanism behaves akin to a damped harmonic oscillator.

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Relationship between wave processes in sunspots and quasi-periodic pulsations in active region flares

Cited by 144 publications

References 27 publications

Multi-height observations of magnetoacoustic cut-off frequency in a sunspot atmosphere

Multi-height observations of magnetoacoustic cut-off frequency in a sunspot atmosphere

Measuring the apparent phase speed of propagating EUV disturbances

On the periodicity of oscillatory reconnection

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