Umbral oscillations in a detailed model umbra

Thomas, John H.; Scheuer, M. A.

doi:10.1007/bf00146970

Cited by 49 publications

(19 citation statements)

References 7 publications

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“…It could well be that umbral flashes are phenomena originating in small structures in the photospheric or the subchromospheric level and then channeled upwards through a narrow path by the magnetic field hence preserving their original localized nature. It has been suggested that umbral flashes are the result of non-linear shock waves propagating upwards (López Ariste et al 2001;Furusawa & Sakai 2000) or that their driving force is trapped magnetoacoustic waves in the photosphere (Thomas & Scheuer 1982) or in the chromosphere itself (Zhugzhda et al 1985). A physical explanation is however beyond the scope of this paper, since a more detailed analysis of the relationship between umbral flashes and the magnetic field vector should be first performed.…”

Section: Discussionmentioning

confidence: 97%

$\ion{Ca}{ ii}$ 8542 Å sunspot oscillations observed with THEMIS

Tziotziou¹,

Tsiropoula²,

Mein³

2002

A&A

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Abstract. Oscillations in the umbra and the penumbra of an isolated sunspot located near the solar disk centre were investigated. The observations were obtained with the Multichannel Subtractive Double Pass (MSDP) spectrograph operating in the Ca ii 8542Å line and installed at the focus of THEMIS (Tenerife). From the MSDP data, two-dimensional intensity and Doppler shift images were computed at different wavelengths within the line. Intensity and Doppler shift oscillations in the umbra and the penumbra of the sunspot showing up as umbral flashes and penumbral waves were analyzed using a 23 min time series with a cadence of 46 s. The Ca ii umbral flash intensity profile shows an emission core in its blue wing. We investigate the relation between umbral flashes and running penumbral waves by a power spectrum analysis which shows a 6 mHz frequency for the standing umbral oscillations (flashes) which are observed only on the upper half part of the umbra. The running penumbral waves propagate with an average phase velocity of 16 km s −1 and their frequency is constant in the penumbra and equal to 3 mHz. Although the time slice images suggest that umbral flashes and running penumbral waves are probably due to the same resonator, the power analysis shows no direct relationship between the two phenomena.

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Section: Discussionmentioning

confidence: 97%

$\ion{Ca}{ ii}$ 8542 Å sunspot oscillations observed with THEMIS

Tziotziou¹,

Tsiropoula²,

Mein³

2002

A&A

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“…According to Zhugzhda and Dzhalilov (1982); Zhugzhda (1984), the fast-mode resonance is essential in producing waves in the 5-min band. Conversely, Thomas and Scheuer (1982); Scheuer and Thomas (1981) calculated numerically the fast-wave resonance, under the assumption that the reflection at the lower boundary is again due to acoustic speed gradients, and the reflection of the upper boundary is due to Alfvén speed gradients, and concluded that this resonance produces a lowest mode with a period of 153 s, i.e., in the 3-min band.…”

Section: Resonance Cavity Model For Chromospheric Wavesmentioning

confidence: 99%

“…This has led to the suggestion that they might be resonant modes of sunspots, with a cavity that might be located either in the sunspot umbra at subphotospheric layers (Scheuer and Thomas, 1981;Thomas and Scheuer, 1982; or at chromospheric layers (von Uexküll et al, 1983;Lites and Thomas, 1985;Gurman, 1987). An interesting relation between the power in a sunspot umbra in the bands of five and three minutes was obtained by Schröter and Soltau (1976), who found that the amplitude of the velocity oscillations in the two bands was anticorrelated, i.e, when one increased the other decreased.…”

Section: Introductionmentioning

confidence: 99%

Oscillations and Waves in Sunspots

Khomenko

Collados

2015

Living Rev. Sol. Phys.

157

118

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A magnetic field modifies the properties of waves in a complex way. Significant advances have been made recently in our understanding of the physics of sunspot waves with the help of high-resolution observations, analytical theories, as well as numerical simulations. We review the current ideas in the field, providing the most coherent picture of sunspot oscillations as by present understanding. Article RevisionsLiving Reviews supports two ways of keeping its articles up-to-date:Fast-track revision. A fast-track revision provides the author with the opportunity to add short notices of current research results, trends and developments, or important publications to the article. A fast-track revision is refereed by the responsible subject editor. If an article has undergone a fast-track revision, a summary of changes will be listed here.Major update. A major update will include substantial changes and additions and is subject to full external refereeing. It is published with a new publication number.For detailed documentation of an article's evolution, please refer to the history document of the article's online version at http://dx

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“…Provided the remaining fast and slow h D n/2, MA waves remain coupled and yield a fourth-order system of ODEs. The lower degree of this system of ODEs makes the ensuing analysis more tractable and easier to interpret (e.g., Ferraro & Plumpton 1958 ;Weymann & Howard 1958 ;Zhugzhda & Dzhalilov 1982 ;Zhugzhda & Dzhalilov 1984b ;Leroy & Schwartz 1982 ;Thomas & Scheuer 1982 ;Schwartz & Bel 1984 ;Zhukov 1985 ;Kamp 1989 ;Campos & Saldanha 1991 ;Hasan & Christensen-Dalsgaard 1992 ;Banerjee, Hasan, & Christensen-Dalsgaard 1995 ;Bogdan & Cally 1997 ;Cally 2001).…”

Section: Uniformly Magnetized Atmospherementioning

confidence: 99%

Waves in the Magnetized Solar Atmosphere. I. Basic Processes and Internetwork Oscillations

Rosenthal

Bogdan

Carlsson

et al. 2002

ApJ

162

181

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We have modeled numerically the propagation of waves through magnetic structures in a stratiÐed atmosphere. We Ðrst simulate the propagation of waves through a number of simple, exemplary Ðeld geometries in order to obtain a better insight into the e †ect of di †ering Ðeld structures on the wave speeds, amplitudes, polarizations, direction of propagation, etc., with a view to understanding the wide variety of wavelike and oscillatory processes observed in the solar atmosphere. As a particular example, we then apply the method to oscillations in the chromospheric network and internetwork. We Ðnd that in regions where the Ðeld is signiÐcantly inclined to the vertical, refraction by the rapidly increasing phase speed of the fast modes results in total internal reÑection of the waves at a surface whose altitude is highly variable. We conjecture a relationship between this phenomenon and the observed spatiotemporal intermittancy of the oscillations. By contrast, in regions where the Ðeld is close to vertical, the waves continue to propagate upward, channeled along the Ðeld lines but otherwise largely una †ected by the Ðeld.

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Umbral oscillations in a detailed model umbra

Cited by 49 publications

References 7 publications

$\ion{Ca}{ ii}$ 8542 Å sunspot oscillations observed with THEMIS

$\ion{Ca}{ ii}$ 8542 Å sunspot oscillations observed with THEMIS

Oscillations and Waves in Sunspots

Waves in the Magnetized Solar Atmosphere. I. Basic Processes and Internetwork Oscillations

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