Observational characteristics and association of umbral oscillations and running penumbral waves

Tziotziou, K.; Tsiropoula, G.; Mein, N.; Mein, P.

doi:10.1051/0004-6361:20064997

Cited by 64 publications

(60 citation statements)

References 16 publications

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“…The gradients a of the best-fitting linear functions obtained for the 1700 Å and 1600 Å data are very close: 0.65 ± 0.03 and 0.64 ± 0.05, respectively. The gradient a in the 304 Å data was 0.81 ± 0.03, in a good agreement with the empirical relation (ν peak 1.25ν mac , Bogdan & Judge 2006;Tziotziou et al 2006). However, we obtained non-zero intercepts in the linear fits, 0.57 ± 0.18 mHz, 0.39 ± 0.34 mHz and −(1.0 ± 0.18) mHz in the 1700 Å, 1600 Å, and 304 Å data, respectively (see Fig.…”

Section: Correlation Between the Cut-off And Peak Frequenciessupporting

confidence: 86%

“…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: Correlation Between the Cut-off And Peak Frequenciessupporting

confidence: 86%

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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“…Both the early works (Sigwarth & Mattig 1997;Kobanov & Makarchik 2004;Tziotziou et al 2006) and recent publications based on SDO data analysis note that lowfrequency oscillations concentrate in regions where the magnetic field lines are significantly inclined (i.e., in the penumbra), whereas the 5 mHz and higher frequency oscillations are concentrated within the umbra boundaries.…”

Section: Resultsmentioning

confidence: 98%

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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“…Running penumbral waves (Giovanelli 1972;Zirin & Stein 1972) are disturbances propagating radially in the form of dark and bright arcs from the inner to the outer penumbral boundaries. Their phase speed is around 10−15 km s −1 and they have a frequency in the five-minute band (Christopoulou et al 2000;Tziotziou et al 2006). In the Hα line centre the waves appear to propagate beyond the outer edge of the penumbra to the superpenumbra.…”

Section: Introductionmentioning

confidence: 99%

Dynamics of the solar atmosphere above a pore with a light bridge

Sobotka

Švanda

Jurčák

et al. 2013

A&A

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Context. Solar pores are small sunspots lacking a penumbra that have a prevailing vertical magnetic-field component. They can include light bridges at places with locally reduced magnetic field. Like sunspots, they exhibit a wide range of oscillatory phenomena. Aims. A large isolated pore with a light bridge (NOAA 11005) is studied to obtain characteristics of a chromospheric filamentary structure around the pore, to analyse oscillations and waves in and around the pore, and to understand the structure and brightness of the light bridge. Methods. Spectral imaging observations in the line Ca II 854.2 nm and complementary spectropolarimetry in Fe I lines, obtained with the DST/IBIS spectrometer and HINODE/SOT spectropolarimeter, were used to measure photospheric and chromospheric velocity fields, oscillations, waves, the magnetic field in the photosphere, and acoustic energy flux and radiative losses in the chromosphere. Results. The chromospheric filamentary structure around the pore has all important characteristics of a superpenumbra: it shows an inverse Evershed effect and running waves, and has a similar morphology and oscillation character. The granular structure of the light bridge in the upper photosphere can be explained by radiative heating. Acoustic waves leaking up from the photosphere along the inclined magnetic field in the light bridge transfer enough energy flux to balance the entire radiative losses of the light-bridge chromosphere. Conclusions. A penumbra is not a necessary condition for the formation of a superpenumbra. The light bridge is heated by radiation in the photosphere and by acoustic waves in the chromosphere.

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Observational characteristics and association of umbral oscillations and running penumbral waves

Cited by 64 publications

References 16 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

Oscillations above sunspots from the temperature minimum to the corona

Dynamics of the solar atmosphere above a pore with a light bridge

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