Observational aspects of sunspot oscillations

Bogdan, Thomas J.; Judge, P. G.

doi:10.1098/rsta.2005.1701

Cited by 160 publications

(131 citation statements)

References 99 publications

(139 reference statements)

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“…The main spectral peak moves to longer periods with the distance from the sunspot's centre. The predominant oscillation inside the umbra is the well-known 3 min oscillation (Bogdan & Judge 2006;De Moortel 2009). The 5 min oscillations form a ring shape at the umbra-penumbra boundary.…”

Section: Discussionmentioning

confidence: 99%

“…studied the travel time of narrowband signals around a sunspot and found good consistency with Bel & Leroy (1977) both in quiet Sun (β 1) and sunspot (β 1) cases. Tziotziou et al (2006) applied the empirical formula ν peak (φ) ≈ 1.25ν mac (φ) (Bogdan & Judge 2006) to estimate the magnetic field inclination in the sunspot's chromosphere, where ν peak denotes the frequency of the maximum peak in the power spectrum, and ν mac represents local MAG cut-off frequency modified by the inclined magnetic field. compared the spectra and phase relations of UV and extreme UV (EUV) emission intensity at various heights of the solar atmosphere and identified the features of upwardly propagating waves.…”

Section: Introductionmentioning

confidence: 99%

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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: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

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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“…Among the many open questions that are unanswered we have for example the role of the residual convection inside the umbra of sunspots and the power reduction of the oscillations in strong magnetic fields. For a detailed treatment of these and many other aspects of waves in sunspots, we refer to Khomenko (2009) and Bogdan & Judge (2006). Simoniello et al (2010) pointed out that the amplitude reduction may be consistent with the MHD mode conversion theory.…”

Section: Introductionmentioning

confidence: 99%

“…Since their discovery (Beckers & Tallant 1969), waves in sunspots have been detected in many solar magnetic features on all spatial scales and at all heights in the atmosphere as small perturbations in both intensity and velocity (Bogdan & Judge 2006;Centeno et al 2009). Nevertheless, a clear understanding of their excitation mechanism and interaction with complex magnetic features remains elusive (Kosovichev 2009).…”

Section: Introductionmentioning

confidence: 99%

Three-minute wave enhancement in the solar photosphere

Stangalini

Giannattasio

Moro

et al. 2012

A&A

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It is a well-known result that the power of five-minute oscillations is progressively reduced by magnetic fields in the solar photosphere. Many authors have pointed out that this could be due to a complex interaction of many processes: opacity effects, MHD mode conversion, and intrinsically weaker acoustic emissivity in strong magnetic fields. While five-minute oscillations predominate in the photosphere, it has been shown that in the chromosphere three-minute oscillations are more common. Two main theories have been proposed to explain the presence of the latter oscillations based upon resonance filtering in the atmospheric cavity and non-linear interactions. In this work, we show, through the analysis of IBIS observations of a solar pore in the photospheric Fe I 617.3 nm line, that three-minute waves are already present at the height of formation of this line, their amplitude depends on the magnetic field strength, and they are strictly confined to the umbral region.

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“…The problem has turned out to be complicated (Bogdan & Judge 2006;Thomas & Weiss 2008). Despite some success in this field, we are still far from a comprehensive understanding of the wave processes in and above sunspots.…”

Section: Introductionmentioning

confidence: 99%

Oscillations above sunspots from the temperature minimum to the corona

Кобанов

Chelpanov

Kolobov

2013

A&A

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Context. An analysis of the oscillations above sunspots was carried out using simultaneous ground-based and Solar Dynamics Observatory (SDO) observations (Si  10827 Å, He  10830 Å, Fe  6173 Å, 1700 Å, He  304 Å, Fe  171 Å). Aims. Investigation of the spatial distribution of oscillation power in the frequency range 1-8 mHz for the different height levels of the solar atmosphere. Measuring the time lags between the oscillations at the different layers. Methods. We used frequency filtration of the intensity and Doppler velocity variations with Morlet wavelet to trace the wave propagation from the photosphere to the chromosphere and the corona. Results. The 15 min oscillations are concentrated near the outer penumbra in the upper photosphere (1700 Å), forming a ring that expands in the transition zone. These oscillations propagate upward and reach the corona level, where their spatial distribution resembles a fan structure. The spatial distribution of the 5 min oscillation power looks like a circle-shape structure matching the sunspot umbra border at the photospheric level. The circle expands at the higher levels (He  304 Å and Fe  171 Å). This indicates that the low-frequency oscillations propagate along the inclined magnetic tubes in the spot. We found that the inclination of the tubes reaches 50−60 degrees in the upper chromosphere and the transition zone. The main oscillation power in the 5-8 mHz range concentrates within the umbra boundaries at all the levels. The highest frequency oscillations (8 mHz) are located in the peculiar points inside the umbra. These points probably coincide with umbral dots. We deduced the propagation velocities to be 28 ± 15 km s −1 , 26 ± 15 km s −1 , and 55 ± 10 km s −1 for the Si  10827 Å-He  10830 Å, 1700 Å-He  304 Å, and He  304 Å-Fe  171 Å height levels, respectively.

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Observational aspects of sunspot oscillations

Cited by 160 publications

References 99 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

Three-minute wave enhancement in the solar photosphere

Oscillations above sunspots from the temperature minimum to the corona

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