Patterns of helicity in solar active regions

Observational Evidence of the Kink Instability in Solar Filament Eruptions and Sigmoids

“…The first and larger loop had positive twist and writhe, while the second had negative twist and writhe. This result should not be surprising, considering that many active regions exhibit patches of both positive-and negative-current helicity (Pevtsov et al 1994). Table 1 shows that in every case, the sense of twist and writhe agreed.…”

A Characteristic Magnetic Field Pattern Associated with All Major Solar Flares and Its Use in Flare Forecasting

“…It has been found, however, that the emergence of electrical currents embedded in magnetic flux, rather than surface shear flows or other purely atmospheric effects, appears to be key in driving active region flaring (e.g., Wheatland 2000a; Démoulin et al 2002aDémoulin et al , 2002bSchrijver et al 2005;Leka & Barnes 2003a, 2003bJing et al 2006;Falconer et al 2002). These strong electrical currents do not persist for more than about a day (e.g., Pevtsov et al 1994;Schrijver et al 2005) unless sustained by continued flux emergence. It is therefore no surprise that the emergence of compact field has also been found to be positively correlated with some flaring (e.g., Schmieder et al 1994;Wang et al 1994;Choudhary et al 1998;Li et al 2000).…”

Active regions on the Sun with high flare productivity and strong geomagnetic efficiency

“…On the other hand the A p decreases when α increases as it can be seen from the Figure 1 (right) and a north-south asymmetry exists. But as it was demonstrated by Pevtsov, Canfield & Metcalf (1994) flares occur when changes in the α are observed in ARs. The small and mean SARs having S 1000 µh seem to differ from the SARs large δ-spots not only by their parameters but also by the relations between them.…”