Photospheric flux cancellation and associated flux rope formation and eruption

By L. Green, B. Kliem, A. Wallace. 2010

183 citations recorded by the source corpus.

Aims. We study an evolving bipolar active region that exhibits flux cancellation at the internal polarity inversion line, the formation of a soft X-ray sigmoid along the inversion line and a coronal mass ejection. The aim is to investigate the quantity of flux cancellation that is involved in flux rope formation in the time period leading up to the eruption.Methods. The active region is studied using its extreme ultraviolet and soft X-ray emissions as it evolves from a sheared arcade to flux rope configuration. The evolution of the photospheric magnetic field is described and used to estimate how much flux is reconnected into the flux rope.Results. About one third of the active region flux cancels at the internal polarity inversion line in the 2.5 days leading up to the eruption. In this period, the coronal structure evolves from a weakly to a highly sheared arcade and then to a sigmoid that crosses the inversion line in the inverse direction. These properties suggest that a flux rope has formed prior to the eruption. The amount of cancellation implies that up to 60% of the active region flux could be in the body of the flux rope. We point out that only part of the cancellation contributes to the flux in the rope if the arcade is only weakly sheared, as in the first part of the evolution. This reduces the estimated flux in the rope to similar to 30% or less of the active region flux. We suggest that the remaining discrepancy between our estimate and the limiting value of similar to 10% of the active region flux, obtained previously by the flux rope insertion method, results from the incomplete coherence of the flux rope, due to nonuniform cancellation along the polarity inversion line. A hot linear feature is observed in the active region which rises as part of the eruption and then likely traces out the field lines close to the axis of the flux rope. The flux cancellation and changing magnetic connections at one end of this feature suggest that the flux rope reaches coherence by reconnection immediately before and early in the impulsive phase of the associated flare. The sigmoid is destroyed in the eruption but reforms quickly, with the amount of cancellation involved being much smaller than in the course of its original formation.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/ecfcf2b22288832212849cbc1a73b5c01b08b6c4

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Citations in the corpus

OBSERVING FLUX ROPE FORMATION DURING THE IMPULSIVE PHASE OF A SOLAR ERUPTION (2011, background): “Recent observations showed that the sigmoid structures, which originally consisted of two opposite J-shaped loops, could be transformed into a flux rope (Liu et al. 2010; Green et al. 2011).”
DIRECT EVIDENCE FOR A FAST CORONAL MASS EJECTION DRIVEN BY THE PRIOR FORMATION AND SUBSEQUENT DESTABILIZATION OF A MAGNETIC FLUX ROPE (2012, background): “…but indirect, evidence for pre-existing flux ropes comes from EUV and SXR observa- tions of the formation and eventual eruption of sigmoids (e.g., Aurass et al. 1999; Canfield et al. 1999; Vrsnak 2003; Green & Kliem 2009; Tripathi et al. 2009; Liu et al. 2010; Green et al. 2011; Huang et al. 2011).”
The standard flare model in three dimensions II: upper limit on solar flare energy (2012, background): “…in past symmetric models (van Ballegooijen & Martens 1989; Amari et al. 2003), and they matched observations and simulations for active regions during their late flux emergence stage and their subsequent decay phase (e.g. van Driel-Gesztelyi et al. 2003; Archontis et al. 2004; Green et al. 2011).”
Solar filament eruptions and their physical role in triggering Coronal Mass Ejections (2012, methodology): “Green et al. (2011) measured the decrease of the flux in a decaying AR during the formation of a sigmoid leading to a CME (Figure 7).”
MAGNETIC FIELD STRUCTURES TRIGGERING SOLAR FLARES AND CORONAL MASS EJECTIONS (2012, background): “…& Kumar 1996; Canfield et al. 1999; Moore et al. 2001), flux cancellation on the photosphere (van Ballegooijen & Martens 1989; Zhang et al. 2001; Green et al. 2011), converging foot point motion (Inhester et al. 1992; Forbes & Priest 1995; Amari et al. 2003a,b; Cheng et al. 2010), the sharp…”
The standard flare model in three dimensions - I. Strong-to-weak shear transition in post-flare loops (2012, background): “Among those are coronal sigmoids (e.g. Aulanier et al. 2010; Green et al. 2011; Savcheva et al. 2012), erupting flux ropes (e.g. Zhang et al. 2012), and bright footpoint emissions moving along ribbons as seen in HXR (e.g. Fletcher & Hudson 2002) and in the EUV (del Zanna et al. 2006; Chandra et al.…”
The standard flare model in three dimensions - III. Slip-running reconnection properties (2013, background): “This double J-shaped current structure found in the present simulation can be related with observations of sigmoids such as reported in Green et al. (2011), and are similar to observations and numerical models discussed in Savcheva et al. (2012).”