Transient Coronal Sigmoids and Rotating Erupting Flux Ropes

Green, L. M.; Kliem, B.; Török, Tibor; Driel-Gesztelyi, L. van; Attrill, G. D. R.

doi:10.1007/s11207-007-9061-z

Cited by 191 publications

(203 citation statements)

References 69 publications

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“…4.2). This difference between the PIL on the Sun and the MC axial direction can be explained by a counter-clockwise rotation of the ejected flux rope, as expected, since its helicity is negative (Török & Kliem 2005;Green et al 2007).…”

Section: Searching For the Solar Sourcesupporting

confidence: 70%

Dynamical evolution of a magnetic cloud from the Sun to 5.4 AU

Nakwacki

Dasso

Démoulin

et al. 2011

A&A

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Context. Significant quantities of magnetized plasma are transported from the Sun to the interstellar medium via interplanetary coronal mass ejections (ICMEs). Magnetic clouds (MCs) are a particular subset of ICMEs, forming large-scale magnetic flux ropes. Their evolution in the solar wind is complex and mainly determined by their own magnetic forces and the interaction with the surrounding solar wind. Aims. Magnetic clouds are strongly affected by the surrounding environment as they evolve in the solar wind. We study expansion of MCs, its consequent decrease in magnetic field intensity and mass density, and the possible evolution of the so-called global ideal-MHD invariants. Methods.In this work we analyze the evolution of a particular MC (observed in March 1998) using in situ observations made by two spacecraft approximately aligned with the Sun, the first one at 1 AU from the Sun and the second one at 5.4 AU. We describe the magnetic configuration of the MC using different models and compute relevant global quantities (magnetic fluxes, helicity, and energy) at both heliodistances. We also tracked this structure back to the Sun, to find out its solar source. Results. We find that the flux rope is significantly distorted at 5.4 AU. From the observed decay of magnetic field and mass density, we quantify how anisotropic is the expansion and the consequent deformation of the flux rope in favor of a cross section with an aspect ratio at 5.4 AU of ≈1.6 (larger in the direction perpendicular to the radial direction from the Sun). We quantify the ideal-MHD invariants and magnetic energy at both locations, and find that invariants are almost conserved, while the magnetic energy decays as expected with the expansion rate found. Conclusions. The use of MHD invariants to link structures at the Sun and the interplanetary medium is supported by the results of this multi-spacecraft study. We also conclude that the local dimensionless expansion rate, which is computed from the velocity profile observed by a single-spacecraft, is very accurate for predicting the evolution of flux ropes in the solar wind.

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Section: Searching For the Solar Sourcesupporting

confidence: 70%

Dynamical evolution of a magnetic cloud from the Sun to 5.4 AU

Nakwacki

Dasso

Démoulin

et al. 2011

A&A

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“…This could be due to the fact that the time scale of the rotation of these filaments is smaller than the cadence of our data. In an independent study using TRACE data Green et al (2007) studied 7 active region filaments which rotated during eruption. In their study, four events were failed eruptions.…”

Section: Discussionmentioning

confidence: 99%

Partially-erupting prominences: a comparison between observations and model-predicted observables

Tripathi

Gibson

Qiu

et al. 2009

A&A

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Aims. We investigate several partially-erupting prominences to study their relationship with other CME-associated phenomena and compare these observations with observables predicted by a model of partially-expelled-flux-ropes (Gibson & Fan 2006a, ApJ, 637, L65; 2006b, J. Geophys. Res., 111, 12103). Methods. We studied 6 selected events with partially-erupting prominences using multi-wavelength observations recorded by the Extreme-ultraviolet Imaging Telescope (EIT), Transition Region and Coronal Explorer (TRACE), Mauna Loa Solar Observatory (MLSO), Big Bear Solar Observatory (BBSO), and Soft X-ray Telescope (SXT). The observational features associated with partiallyerupting prominences were then compared with the predicted observables from the model. Results. The partially-expelled-flux-rope (PEFR) model can explain the partial eruption of these prominences, and in addition predicts a variety of other CME-related observables that provide evidence of internal reconnection during eruption. We find that all of the partially-erupting prominences studied in this paper exhibit indirect evidence of internal reconnection. Moreover, all cases showed evidence of at least one observable unique to the PEFR model, e.g., dimmings external to the source region and/or a soft X-ray cusp overlying a reformed sigmoid. Conclusions. The PEFR model provides a plausible mechanism to explain the observed evolution of partially-erupting-prominenceassociated CMEs in our study.

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“…It is proposed that the ejected helicity is provided by the twist in the sub-photospheric part of the magnetic flux tube forming the active region. Green et al (2007) found the helicity sign of the erupting field and the direction of Solar magnetic fields and helicity 185 filament rotation to be consistent with the conversion of twist into writhe under the ideal MHD constraint of helicity conservation. For positive (negative) helicity the filament apex rotates clockwise (counterclockwise), consistent with the flux rope taking on a reverse (forward) S shape, which is opposite to that observed for the sigmoid.…”

Section: H Zhangmentioning

confidence: 59%

Helicity of solar magnetic field from observations

Zhang

2009

Proc. IAU

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Abstract. The helicity is an important quantity to present the basic topological configuration of magnetic field transferred form the solar subatmosphere into the interplanetary space. In this paper, we present the observational solar magnetic field and the relationship with the magnetic helicity.Keywords. Sun: magnetic fields, helicity, interior; turbulence, MHD Importance and definition of magnetic helicityHelicities are topologically a measure of the structural complexity of the corresponding fields. Woltjer (1958) presented the basic properties of magnetic helicity firstly. As indicated by Taylor (1986) that the topological invariants of ideal plasma so that only total magnetic helicity survives. Helicity is described in terms of the internal structure of a flux tube and the external relations between flux tubes. The helicity of open field configurations not bounded by magnetic surfaces is discussed by Berger and Field (1984), and a measure of the propagation of topological structures across open boundaries is given also. Pouquet, Frisch, and Leorat (1976) indicated that the turbulence and magnetic fields are a common feature of many celestial bodies. The study confirms the importance of helicity both in its kinetic and in its magnetic form for generation of large-scale magnetic fields by turbulence. Keinigs (1983) and Keinigs and Gerwin (1986) analyzed that in a magnetized plasma the alpha effect represents a turbulently generated emf directed along the mean magnetic field. The alpha effect is reevaluated in terms of ensemble-averaged properties of the magnetic fluctuation spectrum. The results indicate that the turbulent current helicity must be opposite in sign to the mean-field current helicity in order for the alpha effect to play a role in overcoming the resistive diffusion of large-scale magnetic fields. Kleeorin and Rogachevskii (1999) analyzed the evolution of the magnetic helicity tensor for a nonzero mean magnetic field and for large magnetic Reynolds numbers in an anisotropic turbulence.The magnetic helicity density h m =A · B, with A the vector potential for magnetic field B, measures the chirality of magnetic lines of force. The magnetic helicity is defined as

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Transient Coronal Sigmoids and Rotating Erupting Flux Ropes

Cited by 191 publications

References 69 publications

Dynamical evolution of a magnetic cloud from the Sun to 5.4 AU

Dynamical evolution of a magnetic cloud from the Sun to 5.4 AU

Partially-erupting prominences: a comparison between observations and model-predicted observables

Helicity of solar magnetic field from observations

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