Initiation of CMEs: the role of magnetic twist

Driel‐Gesztelyi, L. van; Manoharan, P. K.; Démoulin, P.; Aulanier, G.; Mandrini, C. H.; López-Fuentes, M.; Schmieder, B.; Orlando, S.; Thompson, B. J.; Plunkett, S. P.

doi:10.1016/s1364-6826(00)00087-0

Cited by 21 publications

(18 citation statements)

References 54 publications

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“…Magnetic modeling of the observations showed that the cloud could be well approximated with a flux rope of right-handed twist (positive helicity; Lepping et al 1997). It was proposed by van Driel-Gesztelyi et al (2000) that the magnetic cloud was launched from AR 7912: the positive (right-handed) twist of the cloud agreed with the sign of the twist in the expanding coronal loops as indicated by their forward S-shape. We will show below that the magnetic helicity in the AR indeed had a dominantly positive sign.…”

Section: The Active Region Noaa 7912 and The Ldementioning

confidence: 79%

Global budget for an eruptive active region

Bleybel¹,

Amari²,

Driel‐Gesztelyi³

et al. 2002

A&A

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Abstract. We present results on the magnetic structure of NOAA Active Region #7912 which was involved in a long duration flare on 14 October 1995, and was the source region for a magnetic cloud observed by the WIND spacecraft from October 18-20. Using vector magnetograms from the Imaging Vector Magnetograph ("IVM"), we reconstruct the magnetic field above this active region, assuming it is in a non-linear force-free state. This reconstruction is used to determine global properties of the active region magnetic field including topology, magnetic energy, and relative magnetic helicity. A comparison of some global quantities before and after the eruptive event is discussed. We show that the magnetic energy and relative helicity of the active region decreased after the eruption, consistent with the ejection of a large amount of helicity (in the magnetic cloud). We also show that the relaxed post-flare state still contains nonlinearities and is not consistent with a linear force-free state as predicted by Taylor's theory of relaxation. These results agree with those of recent numerical simulations concerning plasmoid ejection and helicity redistribution in the disruption of magnetic configurations. We propose as an explanation that the anchoring of field lines in the photosphere prevents a full cascade to the Taylor state, and that a variational formulation in which the action functional would describe this constraint should be derived.

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Section: The Active Region Noaa 7912 and The Ldementioning

confidence: 79%

Global budget for an eruptive active region

Bleybel¹,

Amari²,

Driel‐Gesztelyi³

et al. 2002

A&A

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“…Comprehensive analyses of the long term evolution of two active regions confirm that evolving magnetic flux density plays an important role in flare and CME activity and its evolution must influence all the activity signatures (van Driel-Gesztelyi et al 1999Green et al 2002). The complex analysis concerns an isolated active region (NOAA 7978 July-December 1996).…”

Section: Evolution Of Magnetic Flux Density Stresses and Activity Thmentioning

confidence: 99%

“…In soft X-rays the region had a sigmoidal shape. Van Driel-Gesztelyi et al (2000) proposed a model involving reconnection in a sheared arcade, which lead to the formation of short, highly sheared loops in the center and long sigmoidal loops connecting the outer edges of the bipole. The long sigmoidal loops may become unstable leading to a CME.…”

Section: Sigmoids Of Small and Large Scalementioning

confidence: 99%

“…In the old days Dodson and Hedeman (1970) postulated that 93% of the flare activity arises in active regions which contain sunspots. However, the span of CME activity is much longer and extends well into the decay phase of active region evolution when the magnetic field is dispersed and the region is classified as quiet solar region containing filament (van Driel-Gesztelyi et al 1999). Subramanian and Dere (2001), based on a sample of 32 CMEs, found that 85% of them were associated with active regions and 15% with so-called quiet regions.…”

Section: Introductionmentioning

confidence: 99%

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Source Regions of Coronal Mass Ejections

Schmieder¹,

Driel‐Gesztelyi²

2004

Proc. IAU

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Abstract. The majority of flare activity arises in active regions which contain sunspots, while CME activity can also originate from decaying active regions and even so-called quiet solar regions which contain a filament. Two classes of CME, namely flare-related CME events and CMEs associated with filament eruption are well reflected in the evolution of active regions, flare related CMEs mainly occur in young active regions containing sunspots and as the magnetic flux of active region is getting dispersed, the filament-eruption related CMEs will become dominant. This is confirmed by statistical analyses.All the CMEs are, nevertheless, caused by loss of equilibrium of the magnetic structure. With observational examples we show that the association of CME, flare and filament eruption depends on the characteristics of the source regions: (i) the strength of the magnetic field, the amount of possible free energy storage, (ii) the small-and large-scale magnetic topology of the source region as well as its evolution (new flux emergence, photospheric motions, canceling flux), and (iii) the mass loading of the configuration (effect of gravity). These examples are discussed in the framework of theoretical models.

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“…Send offprint requests to: B. Kliem, e-mail: bkliem@aip.de Manoharan et al 1996) in AR 7792, which had primarily lefthanded twist (Aurass et al 1999;van Driel-Gesztelyi et al 2000).…”

Section: Introductionmentioning

confidence: 99%

Formation of current sheets and sigmoidal structure by the kink instability of a magnetic loop

Kliem

Titov

Török

2004

A&A

179

133

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Abstract.We study dynamical consequences of the kink instability of a twisted coronal flux rope, using the force-free coronal loop model by as the initial condition in ideal-MHD simulations. When a critical value of the twist is exceeded, the long-wavelength (m = 1) kink mode develops. Analogous to the well-known cylindrical approximation, a helical current sheet is then formed at the interface with the surrounding medium. In contrast to the cylindrical case, upward-kinking loops form a second, vertical current sheet below the loop apex at the position of the hyperbolic flux tube (generalized X line) in the model. The current density is steepened in both sheets and eventually exceeds the current density in the loop (although the kink perturbation starts to saturate in our simulations without leading to a global eruption). The projection of the field lines that pass through the vertical current sheet shows an S shape whose sense agrees with the typical sense of transient sigmoidal (forward or reverse S-shaped) structures that brighten in soft X rays prior to coronal eruptions. The upward-kinked loop has the opposite S shape, leading to the conclusion that such sigmoids do not generally show the erupting loops themselves but indicate the formation of the vertical current sheet below them that is the central element of the standard flare model.

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Initiation of CMEs: the role of magnetic twist

Cited by 21 publications

References 54 publications

Global budget for an eruptive active region

Global budget for an eruptive active region

Source Regions of Coronal Mass Ejections

Formation of current sheets and sigmoidal structure by the kink instability of a magnetic loop

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