Structures and Dynamics of Solar Filaments - challenges in observing and modeling

Engvold, O.

doi:10.1017/s1743921304005575

Cited by 23 publications

(17 citation statements)

References 16 publications

(22 reference statements)

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“…Chiuderi Drago et al 1983;Loukitcheva et al 2004Loukitcheva et al , 2006 are usually based on the VAL (Vernazza et al 1981), FAL (Fontenla et al 1993), and CS (Carlsson & Stein 1992, 1995, 2002) models. Modeling of filaments radio emission (or absorption) is not straightforward, since the results are strongly frequency dependent, especially in the mm and sub-mm wavelength range (Chiuderi Drago 1990;Chiuderi & Chiuderi Drago 1991;Chuideri Drago et al 1992;Engvold 1994;Tandberg-Hanssen 1995). Moreover, many subtle effects should be taken into account, e.g., the influence of the prominence-corona transition region, or the visibility of filament channels and coronal condensations.…”

Section: Introductionmentioning

confidence: 99%

First analysis of solar structures in 1.21 mm full-disc ALMA image of the Sun

Brajša

Sudar

Benz

et al. 2018

A&A

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Context. Various solar features can be seen in emission or absorption on maps of the Sun in the millimeter and submillimeter wavelength range. The recently installed Atacama Large Millimeter/submillimeter Array (ALMA) is capable of observing the Sun in that wavelength range with an unprecedented spatial, temporal and spectral resolution. To interpret solar observations with ALMA the first important step is to compare solar ALMA maps with simultaneous images of the Sun recorded in other spectral ranges. Aims. The first aim of the present work is to identify different structures in the solar atmosphere seen in the optical, infrared and EUV parts of the spectrum (quiet Sun, active regions, prominences on the disc, magnetic inversion lines, coronal holes and coronal bright points) in a full disc solar ALMA image. The second aim is to measure the intensities (brightness temperatures) of those structures and to compare them with the corresponding quiet Sun level. Methods. A full disc solar image at 1.21 mm obtained on December 18, 2015 during a CSV-EOC campaign with ALMA is calibrated and compared with full disc solar images from the same day in Hα line, in He I 1083 nm line core, and with various SDO images (AIA at 170 nm, 30.4 nm, 21.1 nm, 19.3 nm, and 17.1 nm and HMI magnetogram). The brightness temperatures of various structures are determined by averaging over corresponding regions of interest in the calibrated ALMA image. Results. Positions of the quiet Sun, active regions, prominences on the disc, magnetic inversion lines, coronal holes and coronal bright points are identified in the ALMA image. At the wavelength of 1.21 mm active regions appear as bright areas (but sunspots are dark), while prominences on the disc and coronal holes are not discernible from the quiet Sun background, although having slightly less intensity than surrounding quiet Sun regions. Magnetic inversion lines appear as large, elongated dark structures and coronal bright points correspond to ALMA bright points. Conclusions. These observational results are in general agreement with sparse earlier measurements at similar wavelengths. The identification of coronal bright points represents the most important new result. By comparing ALMA and other maps, it was found that the ALMA image was oriented properly and that the procedure of overlaying the ALMA image with other images is accurate at the 5 arc sec level. The potential of ALMA for physics of the solar chromosphere is emphasized.

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Section: Introductionmentioning

confidence: 99%

First analysis of solar structures in 1.21 mm full-disc ALMA image of the Sun

Brajša

Sudar

Benz

et al. 2018

A&A

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“…High-resolution observations have shown that the filament spine is composed of a collection of separate threads (Engvold, 2004;Lin et al, 2005). These threads are believed to be the building blocks of filaments.…”

Section: Introductionmentioning

confidence: 99%

Dependence of the length of solar filament threads on the magnetic configuration

Zhou

Chen

Zhang

et al. 2014

Res. Astron. Astrophys.

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High-resolution Hα observations indicate that filaments consist of an assembly of thin threads. In quiescent filaments, the threads are generally short, whereas in active region filaments, the threads are generally long. In order to explain these observational features, we performed one-dimensional radiative hydrodynamic simulations of filament formation along a dipped magnetic flux tube in the framework of the chromospheric evaporation-coronal condensation model. The geometry of a dipped magnetic flux tube is characterized by three parameters, i.e., the depth (D), the half-width (w), and the altitude (h) of the magnetic dip. The parameter survey in the numerical simulations shows that allowing the filament thread to grow in 5 days, the maximum length (L th ) of the filament thread increases linearly with w, and decreases linearly with D and h. The dependence is fitted into a linear function L th = 0.84w − 0.88D − 2.78h + 17.31 Mm. Such a relation can qualitatively explain why quiescent filaments have shorter threads and active region filaments have longer threads.

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“…They have been interpreted in terms of magnetohydrodynamic (MHD) eigenmodes of the magnetic structure and/or propagating MHD waves. The reader is referred to some recent reviews for more information about the observational and theoretical backgrounds (Oliver & Ballester 2002;Engvold 2004;Ballester 2006;Banerjee et al 2007;Engvold 2008).…”

Section: Introductionmentioning

confidence: 99%

Time damping of non-adiabatic magnetohydrodynamic waves in a partially ionized prominence plasma: effect of helium

Soler

Oliver

Ballester

2010

A&A

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Context. Prominences are partially ionized, magnetized plasmas embedded in the solar corona. Damped oscillations and propagating waves are commonly observed. These oscillations have been interpreted in terms of magnetohydrodynamic (MHD) waves. Ion-neutral collisions and non-adiabatic effects (radiation losses and thermal conduction) have been proposed as damping mechanisms. Aims. We study the effect of the presence of helium on the time damping of non-adiabatic MHD waves in a plasma composed by electrons, protons, neutral hydrogen, neutral helium (He i), and singly ionized helium (He ii) in the single-fluid approximation.Methods. The dispersion relation of linear non-adiabatic MHD waves in a homogeneous, unbounded, and partially ionized prominence medium is derived. We compute the period and the damping time of Alfvén, slow, fast, and thermal waves. A parametric study of the ratio of the damping time to the period with respect to the helium abundance is performed.Results. The efficiency of ion-neutral collisions, as well as thermal conduction, is increased by the presence of helium. However, if realistic abundances of helium in prominences (∼10%) are considered, this has a minor influence on the wave damping. Conclusions. The presence of helium can be safely neglected in studies of MHD waves in partially ionized prominence plasmas.

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Structures and Dynamics of Solar Filaments - challenges in observing and modeling

Cited by 23 publications

References 16 publications

First analysis of solar structures in 1.21 mm full-disc ALMA image of the Sun

First analysis of solar structures in 1.21 mm full-disc ALMA image of the Sun

Dependence of the length of solar filament threads on the magnetic configuration

Time damping of non-adiabatic magnetohydrodynamic waves in a partially ionized prominence plasma: effect of helium

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