Photospheric Magnetic Free Energy Density of Solar Active Regions

TL;DR

This paper investigates the photospheric magnetic energy density in solar active regions using observational data, highlighting the role of magnetic shear and its variation before solar flares.

Contribution

It introduces a method to analyze magnetic energy density and its relation to magnetic shear in active regions, providing insights into flare precursors.

Findings

Magnetic energy density changes before solar flares.

The quantity 1/4pi Bn.Bp reflects magnetic shear contributions.

Magnetic energy density variation correlates with flare activity.

Abstract

We present the photospheric energy density of magnetic fields in two solar active regions inferred from observational vector magnetograms, and compare it with the possible different defined energy parameters of magnetic fields in the photosphere. We analyze the magnetic fields in active region NOAA 6580-6619-6659 and 11158. It is noticed that the quantity 1/4pi Bn.Bp is an important energy parameter that reflects the contribution of magnetic shear on the difference between the potential magnetic field (Bp) and non-potential one (Bn), and also the contribution to the free magnetic energy near the magnetic neutral lines in the active regions. It is found that the photospheric mean magnetic energy density changes obviously before the powerful solar flares in the active region NOAA 11158, it is consistent with the change of magnetic fields in the lower atmosphere with flares.