Ca II H sunspot tomography from the photosphere to the chromosphere

Henriques, V. M. J.; Kiselman, Dan

doi:10.1051/0004-6361/201321656

Cited by 13 publications

(24 citation statements)

References 32 publications

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“…We note that fibril-like structures (often dark) above sunspots have been also reported in observations of the SST narrowband Ca IIH filter (Henriques & Kiselman 2013;Henriques et al 2015).…”

Section: Introductionsupporting

confidence: 81%

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: Introductionsupporting

confidence: 81%

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

Jafarzadeh

Solanki

Gafeira

et al. 2017

ApJS

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“…If one assumes that the dark structures are formed at the same height as the flashes, then the latter is provided by the Ca ii H grain formation heights of Bard & Carlsson (2010), as all the observed intensity enhancement during the flash comes from those spectral features. We note that, while we are observing with a 1.1 Å interference filter, the umbral flashes are chromospheric phenomena and no structures are observed in the inner wing (upper photosphere) of Ca ii H in Henriques & Kiselman (2013). Bard & Carlsson (2010) obtain peaks for the umbral flash formation between 1100 km and 1300 km above the photosphere.…”

Section: Angle Versus Formation Rangementioning

confidence: 62%

“…3 and 4 are available in electronic form at http://www.aanda.org Socas-Navarro et al (2009) in the Ca ii H line core using Hinode, and again at higher resolution (0. 10) by Henriques & Kiselman (2013). These become visible over an area when the bright component of an umbral flash is active in that area.…”

Section: Introductionmentioning

confidence: 97%

Stable umbral chromospheric structures

Henriques

Scullion

Mathioudakis

et al. 2015

A&A

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Aims. We seek to understand the morphology of the chromosphere in sunspot umbra. We investigate if the horizontal structures observed in the spectral core of the Ca ii H line are ephemeral visuals caused by the shock dynamics of more stable structures, and examine their relationship with observables in the H-alpha line.Methods. Filtergrams in the core of the Ca ii H and H-alpha lines as observed with the Swedish 1-m Solar Telescope are employed.We utilise a technique that creates composite images and tracks the flash propagation horizontally. Results. We find 0. 15 wide horizontal structures, in all of the three target sunspots, for every flash where the seeing is moderate to good. Discrete dark structures are identified that are stable for at least two umbral flashes, as well as systems of structures that live for up to 24 min. We find cases of extremely extended structures with similar stability, with one such structure showing an extent of 5 . Some of these structures have a correspondence in H-alpha, but we were unable to find a one-to-one correspondence for every occurrence. If the dark streaks are formed at the same heights as umbral flashes, there are systems of structures with strong departures from the vertical for all three analysed sunspots.Conclusions. Long-lived Ca ii H filamentary horizontal structures are a common and likely ever-present feature in the umbra of sunspots. If the magnetic field in the chromosphere of the umbra is indeed aligned with the structures, then the present theoretical understanding of the typical umbra needs to be revisited.

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“…Nagashima et al (2007) found a node-like feature over the dark umbra where power was suppressed at 5.5 mHz powermaps as seen in Ca II H. Also in Ca II H, Socas-Navarro et al (2009) found dark fibrils in high-resolution Hinode filtergrams, with longitudinal horizontal projections as long as 2000 km. This observation was confirmed in a different sunspot by Henriques & Kiselman (2013). Henriques et al (2015) found that such streaks could be even longer and stable for at least two flashes, with evidence for the presence of the same fibrils over more than three flashes.…”

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confidence: 63%

A Hot Downflowing Model Atmosphere for Umbral Flashes and the Physical Properties of Their Dark Fibrils

Henriques

Mathioudakis

Socas‐Navarro

et al. 2017

ApJ

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Publisher rights © 2017. The American Astronomical Society. All rights reserved. This work is made available online in accordance with the publisher's policies. Please refer to any applicable terms of use of the publisher. General rightsCopyright for the publications made accessible via the Queen's University Belfast Research Portal is retained by the author(s) and / or other copyright owners and it is a condition of accessing these publications that users recognise and abide by the legal requirements associated with these rights.Take down policy The Research Portal is Queen's institutional repository that provides access to Queen's research output. Every effort has been made to ensure that content in the Research Portal does not infringe any person's rights, or applicable UK laws. If you discover content in the Research Portal that you believe breaches copyright or violates any law, please contact openaccess@qub.ac.uk. AbstractWe perform non-LTE inversions in a large set of umbral flashes, including the dark fibrils visible within them, and in the quiescent umbra by using the inversion code NICOLE on a set of full Stokes high-resolution Ca IIλ8542 observations of a sunspot at disk center. We find that the dark structures have Stokes profiles that are distinct from those of the quiescent and flashed regions. They are best reproduced by atmospheres that are more similar to the flashed atmosphere in terms of velocities, even if with reduced amplitudes. We also find two sets of solutions that finely fit the flashed profiles: a set that is upflowing, featuring a transition region that is deeper than in the quiescent case and preceded by a slight dip in temperature, and a second solution with a hotter atmosphere in the chromosphere but featuring downflows close to the speed of sound at such heights. Such downflows may be related, or even dependent, on the presence of coronal loops, rooted in the umbra of sunspots, as is the case in the region analyzed. Similar loops have been recently observed to have supersonic downflows in the transition region and are consistent with the earlier "sunspot plumes," which were invariably found to display strong downflows in sunspots. Finally, we find, on average, a magnetic field reduction in the flashed areas, suggesting that the shock pressure is moving field lines in the upper layers.

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Ca II H sunspot tomography from the photosphere to the chromosphere

Cited by 13 publications

References 32 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

Stable umbral chromospheric structures

A Hot Downflowing Model Atmosphere for Umbral Flashes and the Physical Properties of Their Dark Fibrils

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