Oscillations and Waves in Sunspots

Khomenko, E.; Collados, M.

doi:10.1007/lrsp-2015-6

Cited by 153 publications

(126 citation statements)

References 275 publications

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“…Therefore, some of the waves in our SCFs, particularly close to the left and bottom edges of the ROI, could be excited within the pores, or could at least be influenced by pore waves (e.g., Morton 2012; Khomenko & Collados 2015).…”

Section: The Structures Listed Inmentioning

confidence: 99%

Transverse Oscillations in Slender Ca ii H Fibrils Observed with Sunrise/SuFI

Jafarzadeh

Solanki

Gafeira

et al. 2017

ApJS

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We present observations of transverse oscillations in slender Ca IIH fibrils (SCFs) in the lower solar chromosphere. We use a 1 hr long time series of high-(spatial and temporal-) resolutionseeing-free observations in a 1.1 Å wide passband covering the line core of Ca IIH 3969 Å from the second flight of the SUNRISE balloon-borne solar observatory. The entire field of view, spanning the polarity inversion line of an active region close to the solar disk center, is covered with bright, thin, and very dynamic fine structures. Our analysis reveals the prevalence of transverse waves in SCFs with median amplitudes and periods on the order of 2.4±0.8 km s −1 and 83±29 s, respectively (with standard deviations given as uncertainties). We find that the transverse waves often propagate along (parts of) the SCFs with median phase speeds of 9±14 km s −1. While the propagation is only in one direction along the axis in some of the SCFs, propagating waves in both directions, as well as standing waves are also observed. The transverse oscillations are likely Alfvénic and are thought to be representative of magnetohydrodynamic kink waves. The wave propagation suggests that the rapidhigh-frequency transverse waves,often produced in the lower photosphere, can penetrate into the chromospherewith an estimated energy flux of ≈15 kW m −2. Characteristics of these waves differ from those reported for other fibrillar structures, which, however, were observed mainly in the upper solar chromosphere.

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Section: The Structures Listed Inmentioning

confidence: 99%

Transverse Oscillations in Slender Ca ii H Fibrils Observed with Sunrise/SuFI

Jafarzadeh

Solanki

Gafeira

et al. 2017

ApJS

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“…Several theories also exist to explain the transition of the characteristic frequency from 3.3 mHz in the photosphere to 5.5 mHz in the chromosphere (Zhugzhda et al 1983;Fleck & Schmitz 1991). However, oscillation amplitudes in the photosphere are usually very low, which are further minimized by the opacity effects present in intensity measurements (e.g., Khomenko & Collados 2015). This is perhaps the reason why no bumps are observed in the blue continuum and G-band power spectra.…”

Section: Mean Power Spectramentioning

confidence: 99%

The Frequency-dependent Damping of Slow Magnetoacoustic Waves in a Sunspot Umbral Atmosphere

Prasad

Jess

Doorsselaere

et al. 2017

ApJ

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High spatial and temporal resolution images of a sunspot, obtained simultaneously in multiple optical and UV wavelengths, are employed to study the propagation and damping characteristics of slow magnetoacoustic waves up to transition region heights. Power spectra are generated from intensity oscillations in sunspot umbra, across multiple atmospheric heights, for frequencies up to a few hundred mHz. It is observed that the power spectra display a power-law dependence over the entire frequency range, with a significant enhancement around 5.5 mHz found for the chromospheric channels. The phase difference spectra reveal a cutoff frequency near 3 mHz, up to which the oscillations are evanescent, while those with higher frequencies propagate upward. The power-law index appears to increase with atmospheric height. Also, shorter damping lengths are observed for oscillations with higher frequencies suggesting frequency-dependent damping. Using the relative amplitudes of the 5.5 mHz (3 minute) oscillations, we estimate the energy flux at different heights, which seems to decay gradually from the photosphere, in agreement with recent numerical simulations. Furthermore, a comparison of power spectra across the umbral radius highlights an enhancement of high-frequency waves near the umbral center, which does not seem to be related to magnetic field inclination angle effects.

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“…A sunspot is usually a host of waves and oscillations. In the umbra, the oscillation period is about three minutes, whereas in the penumbra, a dominant oscillation could be found at five minute bandpass (Khomenko & Collados 2015). Above a light bridge, five minute oscillations similar to penumbra oscillations are usually detected, however, its origin is still not revealed yet (Yuan et al 2014;Yuan & Walsh 2016;Yang et al 2015).…”

Section: Introductionmentioning

confidence: 98%

Magnetic Connectivity between the Light Bridge and Penumbra in a Sunspot

Feng

Miao

Yuan

et al. 2020

ApJL

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A light bridge is a prominent structure commonly observed within a sunspot. Its presence usually triggers a wealth of dynamics in a sunspot, and has a lasting impact on sunspot evolution. However, the fundamental structure of light bridges is still not well understood. In this study, we used the high-resolution spectropolarimetry data obtained by the Solar Optical Telescope onboard the Hinode satellite to analyze the magnetic and thermal structure of a light bridge at AR 12838. We also combined the high-cadence 1700Å channel data provided by the Atmospheric Imaging Assembly onboard the Solar Dynamic Observatory to study the dynamics on this bridge. We found that a pair of blue and red Doppler shift patches at two ends of this bridge, this pattern appears to be the convective motion directed by the horizontal component of the magnetic field aligned with the spine of this bridge. Paired upward and downward motions implies that the light bridge could have a two-legged or undulate magnetic field. Significant four minute oscillations in the emission intensity of the 1700Å bandpass were detected at two ends, which had overlap with the paired blue and red shift patches. The oscillatory signals at the light bridge and the penumbra were highly correlated with each other. Although they are separated in space at the photosphere, the periodicity seems to have a common origin from the underneath. Therefore, we infer that the light bridge and penumbra could share a common magnetic source and become fragmented at the photosphere by magneto-convection.

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Oscillations and Waves in Sunspots

Cited by 153 publications

References 275 publications

Transverse Oscillations in Slender Ca ii H Fibrils Observed with Sunrise/SuFI

Transverse Oscillations in Slender Ca ii H Fibrils Observed with Sunrise/SuFI

The Frequency-dependent Damping of Slow Magnetoacoustic Waves in a Sunspot Umbral Atmosphere

Magnetic Connectivity between the Light Bridge and Penumbra in a Sunspot

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