Degree of electric current neutralization and the activity in solar active regions

Abstract

Using time-sequence vector magnetic field observation from Helioseismic and Magnetic Imager, we examined the connection of non-neutralized currents and the observed activity in 20 solar active regions (ARs). The net current in a given magnetic polarity is algebraic sum of direct current (DC) and return current (RC) and the ratio |DC/RC| is a measure of degree of net current neutralization (NCN). In the emerging ARs, the non-neutrality of these currents builds with the onset of flux emergence, following the relaxation to neutrality during the separation motion of bipolar regions. Accordingly, some emerging ARs are source regions of CMEs occurring at the time of higher level non-neutrality. ARs in the post-emergence phase can be CME productive provided they have interacting bipolar regions with converging and shearing motions. In these cases, the net current evolves with higher level (>1.3) of non-neutrality. Differently, the |DC/RC| in flaring and quiet ARs vary near unity. In all the AR samples, the |DC/RC| is higher for chiral current density than that for vertical current density. Owing to the fact that the non-neutralized currents arise in the vicinity of sheared polarity-inversion-lines (SPILs), the profiles of the total length of SPIL segments and the degree of NCN follow each other with a positive correlation. We find that the SPIL is localized as small segments in flaring-ARs, whereas it is long continuous in CME-producing ARs. These observations demonstrate the dividing line between the CMEs and flares with the difference being in global or local nature of magnetic shear in the AR that reflected in non-neutralized currents.