The Formation of a Magnetic Channel by the Emergence of Current-carrying Magnetic Fields

TL;DR

This study investigates the formation of magnetic channels in solar active regions, revealing that they originate from emerging twisted flux tubes and are associated with specific flow patterns and current structures.

Contribution

It provides detailed observational evidence linking magnetic channel formation to the emergence of highly sheared, twisted flux tubes in the solar atmosphere.

Findings

Detection of upflows and downflows at the flux thread tips

Presence of strong vertical currents of opposite polarity

Gradual increase in coronal current density due to flux emergence

Abstract

A magnetic channel - a series of polarity reversals separating elongated flux threads with opposite polarities - may be a manifestation of a highly non-potential magnetic configuration in active regions. To understand its formation we have carried out a detailed analysis of the magnetic channel in AR 10930 using data taken by the Solar Optical Telescope/Hinode. As a result, we found upflows (-0.5 to -1.0 km/s) and downflows (+1.5 to +2.0 km/s) inside and at both tips of the thread respectively, and a pair of strong vertical currents of opposite polarity along the channel. Moreover, our analysis of the nonlinear force-free fields constructed from the photospheric magnetic field indicates that the current density in the lower corona may have gradually increased as a result of the continuous emergence of the highly sheared flux along the channel. With these results, we suggest that the magnetic channel originates from the emergence of the twisted flux tube that has formed below the surface before the emergence.