Buildup of Magnetic Shear and Free Energy During Flux Emergence and Cancellation

TL;DR

This study uses simulations to analyze how magnetic shear and free energy accumulate during flux emergence and cancellation, leading to conditions that can trigger solar eruptive events like CMEs and flares.

Contribution

It provides new insights into the complex magnetic processes and energy buildup during flux emergence and cancellation, highlighting the role of reconnection and shear in solar eruptions.

Findings

Shearing pattern along the PIL builds magnetic shear.

Reconnection produces longer, sheared magnetic field lines.

Energy transfer occurs even during flux submergence and cancellation.

Abstract

We examine a simulation of flux emergence and cancellation, which shows a complex sequence of processes that accumulate free magnetic energy in the solar corona essential for the eruptive events such as coronal mass ejections (CMEs), filament eruptions and flares. The flow velocity at the surface and in the corona shows a consistent shearing pattern along the polarity inversion line (PIL), which together with the rotation of the magnetic polarities, builds up the magnetic shear. Tether-cutting reconnection above the PIL then produces longer sheared magnetic field lines that extend higher into the corona, where a sigmoidal structure forms. Most significantly, reconnection and upward energy-flux transfer are found to occur even as magnetic flux is submerging and appears to cancel at the photosphere. A comparison of the simulated coronal field with the corresponding coronal potential field graphically shows the development of nonpotential fields during the emergence of the magnetic flux and formation of sunspots.