The solar chromosphere at high resolution with IBIS

Vecchio, A.; Cauzzi, G.; Reardon, K.

doi:10.1051/0004-6361:200810694

Cited by 81 publications

(88 citation statements)

References 65 publications

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“…This is consistent with the behavior found by Vecchio et al (2007Vecchio et al ( , 2009 in the chromospheric velocities for this same dataset.…”

Section: Power Mapssupporting

confidence: 92%

“…In Papers I and II of this series (Cauzzi et al 2008;Vecchio et al 2009) we presented novel observations of the Ca II 854.2 nm line of the infrared triplet, obtained with the Interferometric Bidimensional Spectrometer (IBIS, Cavallini 2006). These studies established the suitability of imaging spectroscopy in this line for high-resolution investigations of chromospheric diagnostics.…”

Section: Introductionmentioning

confidence: 99%

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The solar chromosphere at high resolution with IBIS

Reardon

Uitenbroek

Cauzzi

2009

A&A

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Aims. Filtergrams obtained in Ca II H, Ca II K, and Hα are often employed as diagnostics of the solar chromosphere. The vastly disparate appearance between the typical filtergrams in these different lines calls into question the nature of what is actually being observed. We investigate the lack of obvious structures of magnetic origin such as fibrils and mottles in on-disk Ca II H and K images. Methods. We directly compare a temporal sequence of classical Ca II K filtergrams with a co-spatial and co-temporal sequence of spectrally resolved Ca II 854.2 images obtained with the Interferometric Bidimensional Spectrometer (IBIS), considering the effect of both the spectral and spatial smearing. We analyze the temporal behavior of the two series by means of Fourier analysis.Results. The lack of fine magnetic structuring in Ca II K filtergrams, even with the narrowest available filters, is due to observational effects, primarily contributions from the bright, photospheric wings of the line that swamp the small and dark chromospheric structures. Signatures of fibrils remain, however, in the temporal evolution of the filtergrams, in particular with the evidence of magnetic shadows around the network elements. The Ca II K filtergrams do not appear, however, to properly reflect the high-frequency behavior of the chromosphere. Using the same analysis, we find no significant chromospheric signature in the Hinode/SOT Ca II H quiet-Sun filtergrams.Conclusions. The picture provided by Hα and Ca II 854.2, which show significant portions of the chromosphere dominated by magnetic structuring, appears to reflect the true and essential nature of the solar chromosphere. Data that do not resolve this aspect, whether spatially or spectrally, may misrepresent the behavior the chromosphere.

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“…This is consistent with the behavior found by Vecchio et al (2007Vecchio et al ( , 2009 in the chromospheric velocities for this same dataset.…”

Section: Power Mapssupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

The solar chromosphere at high resolution with IBIS

Reardon

Uitenbroek

Cauzzi

2009

A&A

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“…The similarity of lengths and life times of Hα and Ca ii K fibrils was already noted by Marsh (1976). For example, also Hα fibrils (de Pontieu et al 2007a) and Ca ii 8542 Å fibrils (Vecchio et al 2009) are more dynamic in plage and active network than in the quiet Sun. The dynamics of individual fibrils are also similar: fibrils merge, split, fade away, etc.…”

Section: Discussionsupporting

confidence: 57%

Bright fibrils in Ca II K

Pietarila

Hirzberger

Zakharov

et al. 2009

A&A

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Context. Except for the Ca ii resonance lines, fibrils are ubiquitously present in most high-resolution observations of chromospheric lines.Aims. We show that fibrils are also a prevailing feature in Ca ii K, provided the spatial-resolution is sufficiently high. Methods. We present high spatial resolution observations of an active region in the Ca ii K line from the Swedish Solar Telescope.Through a comparison between photospheric intensity and magnetic field data, we study the connection between bright chromospheric fibrils and photospheric structures. Additionally, using Fourier analysis we study how the fibrils are linked to the observed dynamics. Results. We find that very narrow, bright fibrils are a prevailing feature over large portions of the observed field. We also find a clear connection between the fibril footpoints and photospheric magnetic features. We show that the fibrils play two distinct roles in the observed dynamics: depending on their location they can act as a canopy suppressing oscillations or they can channel low-frequency oscillations into the chromosphere.Conclusions. The Ca ii K fibrils share many characteristics with fibrils observed in other chromospheric lines, but some features, such as the very small widths, are unique to these observations.

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“…For the discussion of the validity of semi-empirical (e.g., HSRA, VAL81, FAL93, Fontenla et al 2006;Avrett & Loeser 2008) vs. dynamic chromospheric temperature models (e.g., Carlsson & Stein 1997;Gudiksen et al 2011;WE04), our observations add that both Ca ii lines used here show large rms intensity fluctuations (up to 30%) and a very dynamic behaviour, as also found by Cram & Dame (1983) for Ca ii H, and Cauzzi et al (2008) or Vecchio et al (2009) for the Ca ii IR line at 854.2 nm. This favors dynamical models of the chromosphere more than the semi-empirical approaches that match average spectra without any or with only a low spatial and temporal resolution.…”

Section: Semi-empirical Vs Dynamic Chromospheric Modelssupporting

confidence: 67%

The energy of waves in the photosphere and lower chromosphere

Beck

Rezaei

Puschmann

2012

A&A

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Context. The energy source powering the solar chromosphere is still undetermined, but leaves its traces in observed intensities. Aims. We investigate the statistics of the intensity distributions as a function of the wavelength for Ca ii H and the Ca ii IR line at 854.2 nm to estimate the energy content in the observed intensity fluctuations. Methods. We derived the intensity variations at different heights of the solar atmosphere, as traced by the line wings and line cores of the two spectral lines. We converted the observed intensities to absolute energy units employing reference profiles calculated in non-local thermal equilibrium (NLTE). We also converted the intensity fluctuations to corresponding brightness temperatures assuming LTE. Results. The root-mean-square (rms) fluctuations of the emitted intensity are about 0.6 (1.2) W m −2 ster −1 pm −1 near the core of the Ca ii IR line at 854.2 nm (Ca ii H), corresponding to relative intensity fluctuations of about 20% (30%). For the line wing, we find rms values of about 0.3 W m −2 ster −1 pm −1 for both lines, corresponding to relative fluctuations below 5%. The relative rms values show a local minimum for wavelengths forming at a height of about 130 km, but otherwise increase smoothly from the wing to the core, i.e., from photosphere to chromosphere. The corresponding rms brightness temperature fluctuations are below 100 K for the photosphere and up to 500 K in the chromosphere. The skewness of the intensity distributions is close to zero in the outer line wing and positive throughout the rest of the line spectrum, owing to the frequent occurrence of high-intensity events. The skewness shows a pronounced local maximum at locations with photospheric magnetic fields for wavelengths in-between those of the line wing and the line core (z ≈ 150−300 km), and a global maximum at the very core (z ≈ 1000 km) for both magnetic and field-free locations. Conclusions. The energy content of the intensity fluctuations is insufficient to create a chromospheric temperature rise that would be similar to the one in most reference models of the solar atmosphere. The increase in the rms fluctuations with height indicates the presence of upwardly propagating acoustic waves of increasing oscillation amplitude. The intensity and temperature variations indicate that there is a clear increase in dynamical activity from photosphere towards the chromosphere, but the variations fall short of the magnitude predicted by fully dynamical chromospheric models by a factor of about five. The enhanced skewness between the photosphere and lower solar chromosphere at magnetic locations is indicative of a mechanism that acts solely on magnetized plasma.

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The solar chromosphere at high resolution with IBIS

Cited by 81 publications

References 65 publications

The solar chromosphere at high resolution with IBIS

The solar chromosphere at high resolution with IBIS

Bright fibrils in Ca II K

The energy of waves in the photosphere and lower chromosphere

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