Evolution of Currents of Opposite Signs in the Flare-Productive Solar Active Region Noaa 10930

Abstract

Analysis of a time series of high spatial resolution vector magnetograms of the active region NOAA 10930 available from SOT/SP on-board Hinode revealed that there is a mixture of upward and downward currents in the two foot-points of an emerging flux-rope. The flux emergence rate is almost the same in both the polarities. We observe that along with an increase in magnetic flux, the net current in each polarity increases initially for about three days after which it decreases. This net current is characterized by having exactly opposite signs in each polarities while its magnitude remains almost the same most of the time.The decrease of net current in both the polarities is due to the increase of current having a sign opposite to that of the net current. The dominant current, with same sign as the net current, is seen to increase first and then decreases during the major X-class flares. Evolution of non-dominant current appears to be a necessary condition for a flare initiation. The above observations can have a plausible explanation in terms of the superposition of two different force-free states resulting in non-zero Lorentz force in the corona. This Lorentz force then push the coronal plasma and might facilitate the magnetic reconnection required for flares. Also, the evolution of the net current is found to follow the evolution of magnetic shear at the polarity inversion line.

Flux emergence in the solar active region NOAA 11158: the evolution of net current

“…Parker (1996) argued that some departures from neutralization should be expected on account of insufficient spatial resolution of the magnetographs. However a clear evolution of the observed net current from zero value to a large non-zero value was seen during the emergence of magnetic flux in NOAA AR 10930 (Ravindra et al 2011). It was also noticed that the net current in AR 10930 was chiefly contributed by large sections of highly sheared polarity inversion lines (PILs), a result which had already been demonstrated by Falconer (2001).…”

“…Emergence of magnetic flux seems to be a prime candidate as a flare trigger. In recent times, it is also recognized that emergence of current carrying flux is capable of providing the impetus in the form of a Lorentz force to create the conditions for magnetic reconnection, followed by magnetic eruption, in an otherwise force free coronal environment (Ravindra et al 2011).…”

Modeling the Initiation of the 2006 December 13 Coronal Mass Ejection in Ar 10930: The Structure and Dynamics of the Erupting Flux Rope

“…Guided by the observed photospheric magnetic flux emergence pattern in AR 10930 (e.g., Kubo et al 2007;Min & Chae 2009;Ravindra et al 2011), we impose the emergence of an east-west oriented, left-hand twisted flux rope at the lower boundary. The resulting flux emergence pattern is such that the positive emerging polarity corresponds to the observed positive (counter-clockwise) rotating sunspot emerging against the south end of the pre-existing dominant negative sunspot, and the negative emerging polarity corresponds to the collection of the fragmented negative pores observed to emerge to the west of the δ-spot (Min & Chae 2009).…”

“…The photospheric magnetic field evolution of AR 10930 was well observed by the Solar Optical Telescope (SOT) on board the Hinode satellite over a period of several days before, during, and after the eruption. Many analyses of the observed magnetic flux emergence, build up of current and free magnetic energy, and changes of the photospheric fields associated with the X-class flare have been carried out (e.g., Kubo et al 2007;Zhang et al 2007;Schrijver et al 2008;Gosain et al 2009;Min & Chae 2009;Ravindra & Howard 2010;Ravindra et al 2011). The evolution of AR 10930 was characterized by an emerging δ-sunspot with a growing positive polarity spot against the south edge of a dominant pre-existing negative spot, displaying substantial counter-clockwise rotation and eastward motion as it grew (e.g., Kubo et al 2007;Min & Chae 2009).…”

Distribution of Electric Currents in Sunspots From Photosphere to Corona

“…This is the case in an MHD simulation of an emerging twisted flux tube studied by Török et al (2014), since the flux tube has neutralized currents below the photosphere but develops un-neutralized currents in the corona. Observationally also, such non-neutralized current systems were reported by Ravindra et al (2011) near the polarity inversion line (PIL) in a δ sunspot.…”