A Study of Chromospheric Oscillations Using the<i>SOHO</i>and<i>TRACE</i>Spacecraft

Judge, P. G.; Tarbell, T. D.; Wilhelm, K.

doi:10.1086/321383

Cited by 98 publications

(122 citation statements)

References 48 publications

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“…Our "pure" chromospheric indicator, the 854.2 line core minimum intensity, shows a relative enhancement of the power in the magnetic network in the five-minute regime and the suppression of the three-minute oscillations in the fibrils surrounding the network (the "magnetic shadows", see Judge et al 2001). 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: 86%

“…The distribution of fibrils becomes clearer when taking a temporal average of the Ca II K filtergrams, which shows a slightly decreased intensity surrounding the network magnetic patches corresponding to the location of the fibrils in the Ca II 854.2 line core. A further signature is the presence of the "magnetic shadows" (Judge et al 2001) in the map of three-minute Fourier power derived from the modulation of the radiation temperature in the Ca II K filtergrams. These shadows are similar to those seen in the analogous power maps derived from the Ca II 854.2 line core intensities, but with a more limited spatial extent and an amplitude reduced by one half.…”

Section: Discussionmentioning

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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Section: Power Mapssupporting

confidence: 86%

Section: Discussionmentioning

confidence: 99%

The solar chromosphere at high resolution with IBIS

Reardon

Uitenbroek

Cauzzi

2009

A&A

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“…The rapid time variations seen in the UV continuum and in the transition region lines of S iv and O v are not present in the helium lines. The UV continuum shows properties typical of other QS data sets (e.g., Judge, Tarbell, & Wilhelm 2001). The persistently bright areas in these figures correspond to the chromospheric network (cf.…”

Section: Results For the Quiet-sun Data Obtained On 1996 Octobersupporting

confidence: 53%

On the Formation of Extreme‐Ultraviolet Helium Lines in the Sun: Analysis ofSOHOData

Judge

Pietarila

2004

ApJ

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The resonance lines of helium in the Sun are several times stronger than expected, relative to lines of other ions. To explore the origins of this ''helium enhancement,'' we have studied data from the SUMER, CDS, MDI, and EIT instruments on the Solar and Heliospheric Observatory (SOHO). Time series data obtained in a quiet region and a coronal hole indicate that the spatio-temporal properties of the He i 584 8, and He ii 304 and 1084 8 lines are qualitatively unlike other chromospheric and transition region lines. Helium line intensities vary slowly compared to chromospheric oscillations and to transient transition region brightenings seen in other lines, yet they vary rapidly (both spatially and temporally) compared to the coronal radiation. This suggests that photoionization/recombination plays a minor excitation role in these lines. The Doppler shift of the 584 8 line shows a remarkably clear 4-8 mHz oscillation, with no accompanying line intensity oscillation. Transient brightenings are used to show that nonradial photon scattering might explain the previously found diffuse appearance of the network but cannot account for the reduced network/internetwork intensity contrast in the 584 8 line. We propose a new enhancement mechanism, based on arguments in a companion paper, in which predominantly neutral species such as helium diffuse across magnetic field lines into regions of hot coronal plasma, but charged ions do not. The enhanced internetwork helium emission may arise from the diffusion of helium atoms across the chromospheric canopy; the enhanced network emission may have contributions from diffusion from spicules. This mechanism may naturally explain why the 584 8 line shows Doppler shift, but not intensity, oscillations. Finally, if a mechanism such as ''velocity redistribution'' dominates helium emission, spectroheliograms of helium lines will be bright in regions of large temperature gradients parallel to the magnetic field. Differences between helium and other spectroheliograms may then reveal the relative contributions of ''classical'' and ''cool loop'' models to the observed emission.

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“…Krijger et al (2001) confirmed the presence of power "halos" or "aureoles" in quiet Sun regions around the network patches observed in the UV data obtained with the Transition Region and Coronal Explorer (TRACE). On the other hand, Judge et al (2001), using TRACE UV continua and Solar Ultraviolet Measurements of Emitted Radiation (SUMER) lines, have detected a deficit of acoustic power along with lower intensity values in the 2-3 min period range around the quiet Sun NBPs. This deficit, which they termed "magnetic shadow", had already been reported in previous studies (Kneer & von Uexküll 1986;Cauzzi et al 2000), but it has been further exploited in two-dimensional power maps in the past few years (Krijger et al 2001;Muglach 2003;Muglach et al 2005;Vecchio et al 2007;Reardon et al 2009).…”

Section: Introductionmentioning

confidence: 99%

Power halo and magnetic shadow in a solar quiet region observed in the Hαline

Kontogiannis

Tsiropoula

Tziotziou

2010

A&A

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Context. We investigate the oscillatory behavior of the quiet solar chromosphere and its discrete components in terms of oscillation properties, i.e. network and internetwork. For this purpose, we use a time series of high resolution filtergrams at five wavelengths along the Hα profile, obtained by the Dutch Open Telescope. Aims. We aim to gain insight on the distribution of power in different period bands and its variation between network and internetwork. Our spectral resolution provides information on the vertical distribution of power, since the Hα line has both photospheric and chromospheric components. We investigate the effect of Hα mottles on chromospheric oscillations, since they are the most prominent feature of the Hα chromosphere and outline inclined magnetic fields. Methods. We use wavelet and phase difference analyses of Hα intensities and Doppler signals. Two-dimensional power maps in the 3, 5 and 7 min period bands as well as coherence and phase difference maps were constructed. Results. At photospheric heights, where the Hα ± 0.7 Å wing is formed, the 3 and 5 min power is enhanced around the network, and forms power halos. Higher in the chromosphere these areas are replaced by magnetic shadows, i.e. places of power suppression. Interestingly, the power maps show a filamentary structure in the network which correlates very well with mottles. These areas show positive phase differences at the 3 min period band. At the 5 min and 7 min period bands both positive and negative phase differences are obtained with an increased number of pixels with high coherence, indicating the existence of both upward and downward propagating waves. Conclusions. We attribute our findings to the interaction between acoustic oscillations and the magnetic fields that constitute the magnetic network. The network flux tubes diverge at chromospheric levels and obtain a significant horizontal component, which is betrayed by the presence of mottles. The variation of power reveals the discrete role of the magnetic field at different heights, which guides or suppresses the oscillations, depending on its inclination. Spectral resolution in Hα provides useful information on the coupling between the acoustic sub-canopy atmosphere and the magnetized chromosphere.

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A Study of Chromospheric Oscillations Using theSOHOandTRACESpacecraft

Cited by 98 publications

References 48 publications

The solar chromosphere at high resolution with IBIS

The solar chromosphere at high resolution with IBIS

On the Formation of Extreme‐Ultraviolet Helium Lines in the Sun: Analysis ofSOHOData

Power halo and magnetic shadow in a solar quiet region observed in the Hαline

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