The emergence of toroidal flux tubes from beneath the solar photosphere

Hood, A. W.; Archontis, V.; Galsgaard, K.; Moreno‐Insertis, F.

doi:10.1051/0004-6361/200912189

Cited by 76 publications

(82 citation statements)

References 34 publications

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“…To model the emergence of the top part of a Ω-shaped loop that is rooted much deeper in the interior, an alternative choice of initial flux tube is a toroidal shaped loop. Hood et al (2009) andMacTaggart and describe how to construct an initial toroidal loop. Consider a toroidal flux tube, with the major radius of the torus, R 0 , larger than the minor radius, d. The form of the magnetic field to leading order in an expansion in powers of d/R 0 is based on the cylindrical model.…”

Section: Initial Sub-photospheric Magnetic Fieldmentioning

confidence: 99%

“…In the model by Hood et al (2009), the authors found a rotation of nearly 360 degrees during the emergence of a toroidal flux tube. The dependence of the rotation on the amount of twist, present in the emerging field, and the dynamical evolution of the vortical photospheric motions for different emerging field configurations are presently under investigation.…”

Section: Sunspot Tails Separation and Rotationmentioning

confidence: 99%

“…The rapid expansion of the magnetic field creates a region of reduced pressure (as indicated in Figure 4) and this acts as a sink for draining plasma. Apart from this cavitation, the expanding magnetic field produces another dynamically important effect -shearing along the polarity inversion line (PIL) between the two main photospheric polarities (Manchester, 2001;Fan, 2001;Manchester et al, 2004;Hood et al, 2009;MacTaggart and Hood, 2009). This shearing can be understood by examining the Lorentz force in the direction (y in this case) of the PIL, namely − ∂ ∂y…”

Section: Flux Rope Formationmentioning

confidence: 99%

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3D MHD Flux Emergence Experiments: Idealised Models and Coronal Interactions

Hood

Archontis

MacTaggart³

2011

Sol Phys

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This paper reviews some of the many 3D numerical experiments of the emergence of magnetic fields from the solar interior and the subsequent interaction with the pre-existing coronal magnetic field. The models described here are idealized, in the sense that the internal energy equation only involves the adiabatic, Ohmic and viscous shock heating terms. However, provided the main aim is to investigate the dynamical evolution, this is adequate. Many interesting observational phenomena are explained by these models in a self-consistent manner.

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Section: Initial Sub-photospheric Magnetic Fieldmentioning

confidence: 99%

Section: Sunspot Tails Separation and Rotationmentioning

confidence: 99%

Section: Flux Rope Formationmentioning

confidence: 99%

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3D MHD Flux Emergence Experiments: Idealised Models and Coronal Interactions

Hood

Archontis

MacTaggart³

2011

Sol Phys

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“…The higher the twist and the stronger the magnetic tension are, the greater the tube cohesion is and the faster the instability and emergence occur. Numerical studies predict that the emergence process leads to the formation of a new flux-rope and the development of a sigmoidal structure in the corona (see, e.g., Hood et al, 2009).…”

Section: Introductionmentioning

confidence: 99%

Evidence of Twisted Flux-Tube Emergence in Active Regions

et al. 2014

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Elongated magnetic polarities are observed during the emergence phase of bipolar active regions (ARs). These extended features, called magnetic "tongues", are interpreted as a consequence of the azimuthal component of the magnetic flux in the toroidal flux-tubes that form ARs. We develop a new systematic and user-independent method to identify AR tongues. Our method is based on the determination and analysis of the evolution of the AR main polarity inversion line (PIL). The effect of the tongues is quantified by measuring the acute angle [τ ] between the orientation of the PIL and the direction orthogonal to the AR main bipolar axis. We apply a simple model to simulate the emergence of a bipolar AR. This model lets us interpret the effect of magnetic tongues on parameters that characterize ARs (e.g. the PIL inclination, and the tilt angles and their evolution). In this, idealized kinematic emergence model, τ is a monotonically increasing function of the twist and has the same sign as the magnetic helicity. We systematically apply our procedure to a set of bipolar ARs (41 ARs) that were observed emerging in line-of-sight magnetograms over eight years. For the majority of the cases studied, the presence of tongues has a small influence on the AR tilt angle since tongues have much lower magnetic flux than the more concentrated main polarities. From the observed evolution of τ , corrected by the temporal evolution of the tilt angle and its final value when the AR is fully emerged, we estimate the average number of turns present in the subphotospheric emerging flux-rope. These values for the 41 observed ARs, except one, are below unity. This indicates that sub-photospheric flux-ropes typically have a low amount of twist, i.e. highly twisted flux-tubes are rare. Our results demonstrate that the evolution of the PIL is a robust indicator of the presence of tongues and constrains the amount of twist present in emerging flux-tubes.

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“…In this paper we consider a different geometry for initial the magnetic field -a toroidal flux tube. This model was originally considered by Hood et al (2009). We shall investigate the behaviour of emerging toroidal tubes through a range of initial field strengths and twists.…”

Section: Introductionmentioning

confidence: 99%

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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The emergence of toroidal flux tubes from beneath the solar photosphere

Cited by 76 publications

References 34 publications

3D MHD Flux Emergence Experiments: Idealised Models and Coronal Interactions

3D MHD Flux Emergence Experiments: Idealised Models and Coronal Interactions

Evidence of Twisted Flux-Tube Emergence in Active Regions

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

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