Flux Emergence in the Solar Active Region NOAA 11158: The Evolution of Net Current

TL;DR

This study analyzes the evolution of net vertical current in NOAA 11158, linking magnetic field changes to eruptive solar events and demonstrating how flux emergence influences current dynamics.

Contribution

It provides a detailed observational analysis of net current evolution in an active region, connecting magnetic topology changes to solar eruptions.

Findings

Net current peaks before sunspot separation in CME region

Net current increases with sunspot rotation rate

Sudden net current increase during strong flare

Abstract

We present a detailed investigation on the evolution of observed net vertical current using a time series of vector magnetograms of the active region (AR) NOAA 11158 obtained from Helioseismic Magnetic Imager. We also discuss the relation of net current to the observed eruptive events. The AR evolved from $\beta\gamma$ to $\beta\gamma\delta$ configuration over a period of 6 days. The AR had two sub-regions of activity with opposite chirality: one dominated by sunspot rotation producing a strong CME, the other showing large shear motions producing a strong flare. The net current in each polarity over the CME producing sub-region increased to a maximum and then decreased when the sunspots got separated. The time profile of net current in this sub-region followed the time profile of the rotation rate of the S-polarity sunspot of the same sub-region. The net current in the flaring sub-region showed a sudden increase at the time of the strong flare and remained unchanged till the end of the observation, while the sunspots maintained their close proximity. The systematic evolution of the observed net current is seen to follow the time evolution of total length of strongly sheared polarity inversion lines in both the sub-regions. The observed photospheric net current could be explained as an inevitable product of the emergence of a twisted flux rope, from a higher pressure confinement below the photosphere into the lower pressure environment of the photosphere.