The Emergence of a Twisted Ω-Tube into the Solar Atmosphere

Fan, Yuhong

doi:10.1086/320935

Cited by 291 publications

(331 citation statements)

References 10 publications

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“…This value is smaller than those used in previous studies (Fan 2001;Murray et al 2006;Archontis & Török 2008;Hood et al 2009) and is believed to be more applicable to the Sun. We follow the evolution for the cases B 0 = 1, 3, 5, 7 and 9.…”

Section: Varying B 0 With Fixed α: General Dynamicsmentioning

confidence: 56%

On the emergence of toroidal flux tubes: general dynamics and comparisons with the cylinder model

MacTaggart¹,

Hood²

2009

A&A

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Aims. In this paper we study the dynamics of toroidal flux tubes emerging from the solar interior, through the photosphere and into the corona. Many previous theoretical studies of flux emergence use a twisted cylindrical tube in the solar interior as the initial condition. Important insights can be gained from this model, however, it does have shortcomings. The axis of the tube never fully emerges as dense plasma becomes trapped in magnetic dips and restrains its ascent. Also, since the entire tube is buoyant, the main photospheric footpoints (sunspots) continually drift apart. These problems make it difficult to produce a convincing sunspot pair. We aim to address these problems by considering a different initial condition, namely a toroidal flux tube. Methods. We perform numerical experiments and solve the 3D MHD equations. The dynamics are investigated through a range of initial field strengths and twists.Results. The experiments demonstrate that the emergence of toroidal flux tubes is highly dynamic and exhibits a rich variety of behaviour. In answer to the aims, however, if the initial field strength is strong enough, the axis of the tube can fully emerge. Also, the sunspot pair does not continually drift apart. Instead, its maximum separation is the diameter of the original toroidal tube.

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Section: Varying B 0 With Fixed α: General Dynamicsmentioning

confidence: 56%

On the emergence of toroidal flux tubes: general dynamics and comparisons with the cylinder model

MacTaggart¹,

Hood²

2009

A&A

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“…We expect some minimum amount of preexisting twist in the magnetic structure as it emerges through the photosphere, for the following reasons: It has been found that a minimum amount of twist is needed to ensure that flux tubes rise cohesively through the convection zone (e.g., Emonet & Moreno-Insertis 1998;Fan, Zweibel, & Lantz 1998;Abbett, Fisher, & Fan 2000, 2001. Moreover, vector magnetogram observations imply that this twist is still there when magnetic structures emerge through the photosphere (e.g., Leka et al 1996;Tanaka 1991).…”

Section: Discussionmentioning

confidence: 99%

The Structure and Evolution of a Sigmoidal Active Region

Gibson

Fletcher

Zanna

et al. 2002

ApJ

140

125

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Solar coronal sigmoidal active regions have been shown to be precursors to some coronal mass ejections. Sigmoids, or S-shaped structures, may be indicators of twisted or helical magnetic structures, having an increased likelihood of eruption. We present here an analysis of a sigmoidal region's three-dimensional structure and how it evolves in relation to its eruptive dynamics. We use data taken during a recent study of a sigmoidal active region passing across the solar disk (an element of the third Whole Sun Month campaign). While S-shaped structures are generally observed in soft X-ray (SXR) emission, the observations that we present demonstrate their visibility at a range of wavelengths including those showing an associated sigmoidal filament. We examine the relationship between the S-shaped structures seen in SXR and those seen in cooler lines in order to probe the sigmoidal region's three-dimensional density and temperature structure. We also consider magnetic field observations and extrapolations in relation to these coronal structures. We present an interpretation of the disk passage of the sigmoidal region, in terms of a twisted magnetic flux rope that emerges into and equilibrates with overlying coronal magnetic field structures, which explains many of the key observed aspects of the region's structure and evolution. In particular, the evolving flux rope interpretation provides insight into why and how the region moves between active and quiescent phases, how the region's sigmoidicity is maintained during its evolution, and under what circumstances sigmoidal structures are apparent at a range of wavelengths.

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“…In these realistic models the radiative transfer in the lower atmosphere is treated as well as the heat conduction and radiation needed in the coronal part. Descriptions of the flux tube emergence into the corona on larger scales, more representative of an active region, had to omit the realistic description allowing for the synthesis of photospheric and coronal emission (e.g., Fan 2001;Abbett & Fisher 2003;Manchester et al 2004;Archontis et al 2004;Magara 2006). Hurlburt et al (2002) used a 2D axisymmetric magneto-convection sunspot model to construct the coronal magnetic field above.…”

Section: Introductionmentioning

confidence: 99%

A model for the formation of the active region corona driven by magnetic flux emergence

Chen

Peter

Bingert

et al. 2014

A&A

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Aims. We present the first model that couples the formation of the corona of a solar active region to a model of the emergence of a sunspot pair. This allows us to study when, where, and why active region loops form, and how they evolve. Methods. We use a 3D radiation magnetohydrodynamics (MHD) simulation of the emergence of an active region through the upper convection zone and the photosphere as a lower boundary for a 3D MHD coronal model. The coronal model accounts for the braiding of the magnetic fieldlines, which induces currents in the corona to heat up the plasma. We synthesize the coronal emission for a direct comparison to observations. Starting with a basically field-free atmosphere we follow the filling of the corona with magnetic field and plasma. Results. Numerous individually identifiable hot coronal loops form, and reach temperatures well above 1 MK with densities comparable to observations. The footpoints of these loops are found where small patches of magnetic flux concentrations move into the sunspots. The loop formation is triggered by an increase in upward-directed Poynting flux at their footpoints in the photosphere. In the synthesized extreme ultraviolet (EUV) emission these loops develop within a few minutes. The first EUV loop appears as a thin tube, then rises and expands significantly in the horizontal direction. Later, the spatially inhomogeneous heat input leads to a fragmented system of multiple loops or strands in a growing envelope.

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The Emergence of a Twisted Ω-Tube into the Solar Atmosphere

Cited by 291 publications

References 10 publications

On the emergence of toroidal flux tubes: general dynamics and comparisons with the cylinder model

On the emergence of toroidal flux tubes: general dynamics and comparisons with the cylinder model

The Structure and Evolution of a Sigmoidal Active Region

A model for the formation of the active region corona driven by magnetic flux emergence

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