A New Magnetic Parameter of Active Regions Distinguishing Large Eruptive and Confined Solar Flares
Ting Li Submitted: 2022-02-20 20:30
With the aim of investigating how the magnetic field in solar active regions (ARs) controls flare activity, i.e., whether a confined
or eruptive flare occurs, we analyze 106 flares of Geostationary Operational Environmental
Satellite (GOES) class ≥M1.0 during 2010-2019. We calculate mean characteristic twist parameters α FPIL within the ``flaring polarity
inversion line" region and α _HFED within the area of high photospheric magnetic free energy
density, which both provide measures of the nonpotentiality of AR core region. Magnetic twist is thought to be related to the driving force of electric current-driven
instabilities, such as the helical kink instability.
We also calculate total unsigned magnetic flux (Φ_AR) of ARs producing the flare, which
describes the strength of the background field confinement. By considering both the constraining effect of background
magnetic fields and the magnetic non-potentiality of ARs, we propose a new parameter α /Φ_AR to measure the probability for a large flare to be associated with a coronal mass ejection (CME).
We find that in about 90% of eruptive flares, α _FPIL/Φ_AR and α _HFED/Φ_AR are beyond critical values (2.2x10-24
and 3.2x10-24 Mm-1 Mx-1),
whereas they are less than critical values in ~ 80% of
confined flares. This indicates that the new parameter α /Φ_AR is well able to distinguish eruptive flares from confined flares.
Our investigation suggests that the relative measure of magnetic nonpotentiality within the AR core over the restriction of the background field
largely controls the capability of ARs to produce eruptive flares.
Authors: Ting Li, Xudong Sun, Yijun Hou, Anqin Chen, Shuhong Yang and Jun Zhang
Publication Status: 2022, ApJL, 926, L14
Last Modified: 2022-02-21 07:42