Magnetic structure of an activated filament in a flaring active region

Sasso, C.; Lagg, A.; Solanki, S. K.

doi:10.1051/0004-6361/201322481

Cited by 30 publications

(33 citation statements)

References 65 publications

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“…4), when the new Hα filament has formed, is consistent with previous such measurements (Lites 2005;Okamoto et al 2008;Lites et al 2010;Xu et al 2012;Sasso et al 2014). At several locations within the PIL higher fields strengths of up to 800 G at log(τ) = −2 can be observed, which appear to be somewhat short lived, since they can never be observed at the same place in consecutive SOT/SP scans.…”

Section: Discussionsupporting

confidence: 91%

Formation of a solar Hαfilament from orphan penumbrae

Buehler

Lagg

Noort

et al. 2016

A&A

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Aims. The formation and evolution of an Hα filament in active region (AR) 10953 is described. Methods. Observations from the Solar Optical Telescope (SOT) aboard the Hinode satellite starting from UT 18:09 on 27th April 2007 until UT 06:08 on 1st May 2007 were analysed. 20 scans of the 6302 Å Fe I line pair recorded by SOT/SP were inverted using the spatially coupled version of the SPINOR code. The inversions were analysed together with co-spatial SOT/BFI G-band and Ca II H and SOT/NFI Hα observations. Results. Following the disappearance of an initial Hα filament aligned along the polarity inversion line (PIL) of the AR, a new Hα filament formed in its place some 20 h later, which remained stable for, at least, another 1.5 days. The creation of the new Hα filament was driven by the ascent of horizontal magnetic fields from the photosphere into the chromosphere at three separate locations along the PIL. The magnetic fields at two of these locations were situated directly underneath the initial Hα filament and formed orphan penumbrae already aligned along the Hα filament channel. The 700 G orphan penumbrae were stable and trapped in the photosphere until the disappearance of the overlying initial Hα filament, after which they started to ascend into the chromosphere at 10 ± 5 m/s. Each ascent was associated with a simultaneous magnetic flux reduction of up to 50% in the photosphere. The ascended orphan penumbrae formed dark seed structures in Hα in parallel with the PIL, which elongated and merged to form an Hα filament. The filament channel featured horizontal magnetic fields of on average 260 G at log(τ) = −2 suspended above the nearly field-free lower photosphere. The fields took on an overall inverse configuration at log(τ) = −2 suggesting a flux rope topology for the new Hα filament. The destruction of the initial Hα filament was likely caused by the flux emergence at the third location along the PIL. Conclusions. We present a new interpretation of the Hα filament formation in AR 10953 whereby the mainly horizontal fields of orphan penumbrae, aligned along the Hα filament channel, ascend into the chromosphere, forming seed fragments for a new, second Hα filament. The orphan penumbral fields ascend into the chromosphere ∼9-24 h before the Hα filament is fully formed.

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Section: Discussionsupporting

confidence: 91%

Formation of a solar Hαfilament from orphan penumbrae

Buehler

Lagg

Noort

et al. 2016

A&A

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“…Although the flux-rope model is consistent with many active-region filaments (e.g., Dudík et al 2008;Canou & Amari 2010;Sasso et al 2014;Liu et al 2014aLiu et al , 2016, more complicated magnetic configurations are not rare. For example, Guo et al (2010) found that a flux rope and a sheared arcade match two sections of a filament separately.…”

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confidence: 66%

Double-decker Filament Configuration Revealed by Mass Motions

Awasthi

Liu

Wang

2019

ApJ

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It is often envisaged that dense filament material lies in the dips of magnetic field lines belonging to either a sheared arcade or a magnetic flux rope. But it is also debated which configuration correctly depicts filaments' magnetic structure, due to our incapacity to measure the coronal magnetic field. In this paper, we address this issue by employing mass motions in an active-region filament to diagnose its magnetic structure. The disturbance in the filament was driven by a surge initiated at the filament's eastern end in the NOAA active region 12685, which was observed by the 1-m New Vacuum Solar Telescope (NVST) in the Hα line center and line wing (±0.4Å). Filament material predominately exhibits two kinds of motions, namely, rotation about the spine and longitudinal oscillation along the spine. The former is evidenced by antisymmetric Doppler shifts about the spine; the latter features a dynamic barb with mass extending away from the Hα spine until the transversal edge of the EUV filament channel. The longitudinal oscillation in the eastern section of the filament is distinct from that in the west, implying that the underlying field lines have different lengths and curvature radii. The composite motions of filament material suggest a double-decker host structure with mixed signs of helicity, comprising a flux rope atop a sheared-arcade system.

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“…Leroy et al, 1984;Bommier et al, 1994;Parenti, 2014;Ouyang et al, 2017), the flux ropes with a normal configuration are usually observed in the vicinity of active regions (see e.g. Okamoto et al, 2008;Guo et al, 2010;Kuckein et al, 2012;Sasso et al, 2014), and can be responsible for fast CMEs (Low and Zhang, 2002). The horizontal equilibrium of the prominence in such a magnetic system is provided automatically because of the horizontal symmetry of the model, while the vertical equilibrium is determined by the balance of the gravity force F g and three Lorentz forces F 1 , F 2 , and F m acting on the prominence from the external photospheric and mirror currents, respectively.…”

Section: Model and Governing Equationsmentioning

confidence: 99%

Finite amplitude transverse oscillations of a magnetic rope

Kolotkov

Nisticò

Rowlands

et al. 2018

Journal of Atmospheric and Solar-Terrestrial Physics

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The effects of finite amplitudes on the transverse oscillations of a quiescent prominence represented by a magnetic rope are investigated in terms of the model proposed by Kolotkov et al. (2016). We consider a weakly nonlinear case governed by a quadratic nonlinearity, and also analyse the fully nonlinear equations of motion. We treat the prominence as a massive line current located above the photosphere and interacting with the magnetised dipped environment via the Lorentz force. In this concept the magnetic dip is produced by two external current sources located at the photosphere. Finite amplitude horizontal and vertical oscillations are found to be strongly coupled between each other. The coupling is more efficient for larger amplitudes and smaller attack angles between the direction of the driver and the horizontal axis. Spatial structure of oscillations is represented by Lissajous-like curves with the limit cycle of a hourglass shape, appearing in the resonant case, when the frequency of the vertical mode is twice the horizontal mode frequency. A metastable equilibrium of the prominence is revealed, which is stable for small amplitude displacements, and becomes horizontally unstable, when the amplitude exceeds a threshold value. The maximum oscillation amplitudes are also analytically derived and analysed. Typical oscillation periods are determined by the oscillation amplitude, prominence current, its mass and position above the photosphere, and the parameters of the magnetic dip. The main new effects of the finite amplitude are the coupling of the horizontally and vertically polarised transverse oscillations (i.e. the lack of a simple, elliptically polarised regime) and the presence of metastable equilibria of prominences.

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Magnetic structure of an activated filament in a flaring active region

Cited by 30 publications

References 65 publications

Formation of a solar Hαfilament from orphan penumbrae

Formation of a solar Hαfilament from orphan penumbrae

Double-decker Filament Configuration Revealed by Mass Motions

Finite amplitude transverse oscillations of a magnetic rope

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