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

TL;DR

This study analyzes high-resolution vector magnetograms of active region NOAA 10930, revealing the evolution of opposite-signed currents and their relation to solar flares, highlighting the role of current dynamics in flare initiation.

Contribution

It provides new insights into the evolution of currents of opposite signs in an active region and their connection to flare activity, based on detailed magnetogram analysis.

Findings

Opposite-signed currents coexist in flux-rope footpoints.

Net current increases then decreases with flux emergence and flare activity.

Evolution of net current correlates with magnetic shear at the inversion line.

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.