Formation of a Solar Filament Channel

Gaizauskas, V.; Zirker, J. B.; Sweetland, Charles; Kovács, Ágnes Melinda

doi:10.1086/512788

Cited by 106 publications

(88 citation statements)

References 17 publications

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“…In panels (b)-(d), we note a sigmoidcusp-sigmoid morphology transition over the region, also modelled by [20], and often observed in the coronal soft X-rays above the source regions of homologous eruptions [21]. Here, the inverse-S-shaped flux rope is formed due to reconnections inside the current sheet followed by the shearing photospheric foot point motions, flux convergence and cancellation; supporting earlier observations by [22,23] and simulations of [24,25], rather than subsurface flux tubes of Figure 2 (b) bodily emerging into the photosphere. Figure 5 (e) shows strong shear at the polarity-reversal line between the spots which continuously pump twist and magnetic energy into the atmosphere in the form of a sustained Poynting flux ∼ 6 × 10 8 ergs s −1 cm −2 or 2 × 10 27 ergs s −1 over the area of the box shown in Figure 3.…”

supporting

confidence: 87%

Modeling Repeatedly FlaringδSunspots

Chatterjee¹,

Hansteen²,

Carlsson³

2016

Phys. Rev. Lett.

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Active regions (AR) appearing on the surface of the Sun are classified into α, β, γ, and δ by the rules of the Mount Wilson Observatory, California on the basis of their topological complexity. Amongst these, the δ-sunspots are known to be super-active and produce the most X-ray flares. Here, we present results from a simulation of the Sun by mimicking the upper layers and the corona, but starting at a more primitive stage than any earlier treatment. We find that this initial state consisting of only a thin sub-photospheric magnetic sheet breaks into multiple flux-tubes which evolve into a colliding-merging system of spots of opposite polarity upon surface emergence, similar to those often seen on the Sun. The simulation goes on to produce many exotic δ-sunspot associated phenomena: repeated flaring in the range of typical solar flare energy release and ejective helical flux ropes with embedded cool-dense plasma filaments resembling solar coronal mass ejections.Delta-sunspots are formed when two sunspots of opposite polarity magnetic field appear very close to each other and reside in the same penumbra, the radial filamentary structure outside the umbral region of the strongest magnetic fields. Strong shear and horizontal magnetic fields often exist at the polarity-inversion line separating the two polarities [1]. The subsurface processes which form the δ-sunspots are still debated. Early observational studies [2,3] propose that δ-sunspots form from collision-merging of topologically separate dipoles, while numerical simulations by [4,5] show that kink unstable magnetic flux-tube -helical field lines winding around a central axis -emerging from the subsurface can have a δ-sunspot like structure. More recently, attempts to model the δ-spot in the NOAA AR 11158 utilized a uniformly twisted sub-surface flux-tube initially buoyant in two adjacent regions along its length [6,7]. Also, [8] found a magnetic flux concentration resembling a δ sunspot in their stratified helical dynamo simulation. These studies did not report any flaring activity. On the other hand [9] initialized their simulation with two parallel flux-tubes each lying at a different depth from the surface and with a different value of the initial magnetic twist which later evolved into a δ-sunspot like structure and powered multiple reconnection events. Delta-sunspots are highly flare-productive -95% of the strongest (X-class) X-ray flares originate from these regions [3]. Using a realistic numerical simulation [10] showed that interaction between adjacent expanding magnetic bipoles pressing against each other can lead to the formation of strong current layers in the atmosphere which in turn lead to repeated flaring in the region. Here, we report on a three-dimensional magneto-hydrodynamic (MHD) simulation of the formation of a δ-sunpot like region as a result of the break-up of a cool magnetic layer embedded in the upper solar convection zone into several flux-tubes due to the growth of three-dimensional unstable modes excited in the layer. This instab...

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supporting

confidence: 87%

Modeling Repeatedly FlaringδSunspots

Chatterjee¹,

Hansteen²,

Carlsson³

2016

Phys. Rev. Lett.

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“…Even though we have not directly measured the helicity injection while the filament channel formed, previous studies supports our conjecture above that the helicity of a filament channel would also come from the coronal structure of its associated active region not directly from below the photosphere while it formed. Gaizauskas et al (1997) presented that a filament channel formed at the boundary of an active region while the active region emerged in a previously quiet region. Since an emerging active region carries its magnetic helicity (Leka et al 1996;Jeong & Chae 2007) and at the boundary where the filament formed, helicity injection is negligible (Welsch & Longcope 2003), helicity of filament channel may be provided from the emerging active region, which is consistent with our finding.…”

Section: Discussionmentioning

confidence: 99%

“…Since an emerging active region carries its magnetic helicity (Leka et al 1996;Jeong & Chae 2007) and at the boundary where the filament formed, helicity injection is negligible (Welsch & Longcope 2003), helicity of filament channel may be provided from the emerging active region, which is consistent with our finding. Soon after the observation by Gaizauskas et al (1997), studies using a force-free field model to account for this specific channel formation were done (Mackay et al 1997;Mackay et al 1998). The models suggest that the formation of the filament channel is due to the emerging activity complex in a sheared state.…”

Section: Discussionmentioning

confidence: 99%

“…Coronal arcades overlying a filament are also a constituent of overall surrounding structure (Martin 1990;Satio & Tandberg-Hanssen 1973). A region showing these characteristics is known as a filament channel (Martin 1990;Gaizauskas et al 1997;Gaizauskas 1998). All these necessary conditions for the formation of filaments have been well discussed (e.g., Martin 1998).…”

Section: Introductionmentioning

confidence: 99%

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Magnetic Helicity Injection During the Formation of an Intermediate Filament

Jeong¹,

Chae²,

Moon³

2009

Journal of The Korean Astronomical Society

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A necessary condition for the formation of a filament is magnetic helicity. In the present paper we seek the origin of magnetic helicity of intermediate filaments. We observed the formation of a sinistral filament at the boundary of a decaying active region using full-disk H α images obtained from Big Bear Solar Observatory. We have measured the rate of helicity injection during the formation of the filament using full-disk 96 minute-cadence magnetograms taken by SOHO MDI. As a result we found that 1) no significant helicity was injected around the region (polarity inversion line; PIL) of filament formation and 2) negative helicity was injected in the decaying active region. The negative sign of the injected helicity was opposite to that of the filament helicity. On the other hand, at earlier times when the associated active region emerged and grew, positive helicity was intensively injected. Our results suggest that the magnetic helicity of the intermediate filament may have originated from the helicity accumulated during the period of the growth of its associated active region.

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“…There are however few observations of their formation (e.g. Gaizauskas et al 1997Gaizauskas et al , 2001, and it is not clearly understood why they form all over the Sun (see for example the review by Mackay et al 2010). They also point out that the precise localization of the filament formation along the PIL is still an open question.…”

Section: Filaments and The Magnetic Configurationmentioning

confidence: 99%

Filaments and the magnetic configuration. I. Observation of the solar case

Meunier

Delfosse

2011

A&A

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Context. The emission of Ca and Hα is correlated for the Sun, but this does not seem to be true for other stars. We previously demonstrated that this lack of correlation could be due to the presence of filaments. Aims. We aim to establish a link between the activity level, the magnetic configuration, and the number of filaments, and therefore with observables of other stars that the Sun. Methods. We studied the relationship between the filaments and the magnetic configuration using a large scale approach on MDI/SOHO magnetograms and a large sample of filaments. We validated the reconstruction of synthetic time series of filament surface coverage representative of the magnetic configuration, and then apply it to observations over a full solar cycle. Results. We derived quantitative criteria that relates the presence of filaments to the properties at polarity inversion lines, hereafter PIL, magnetic field gradient, and unipolar areas on the solar surface (size and distance to these areas). We also observed that the number of PIL pixels is anti-correlated with the activity level, and the increase in filament surface coverage is due to the modification of the PIL pixel properties. We reconstructed synthetic time series of filaments that are in good agreement with observations. Conclusions. This work validates our method, which will later be applied to solar and stellar simulations.

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Formation of a Solar Filament Channel

Cited by 106 publications

References 17 publications

Modeling Repeatedly FlaringδSunspots

Modeling Repeatedly FlaringδSunspots

Magnetic Helicity Injection During the Formation of an Intermediate Filament

Filaments and the magnetic configuration. I. Observation of the solar case

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