Magnetic imprints of eruptive and non-eruptive Solar flares as observed by Solar Dynamics Observatory

TL;DR

This study systematically analyzes photospheric magnetic field changes during 21 solar flares, revealing that magnetic imprints correlate with flare strength but do not distinguish eruptive from non-eruptive events, supporting feedback from corona to photosphere.

Contribution

It provides a comprehensive analysis of magnetic imprints in both eruptive and non-eruptive flares using high-cadence data, highlighting their similarities and correlations with flare strength.

Findings

Magnetic imprints are localized in eruptive flares but scattered in most non-eruptive flares.

The strength of magnetic imprints correlates with flare strength regardless of eruptivity.

Free energy decreases during flares and correlates with Lorentz force changes, indicating energy release into the photosphere.

Abstract

The abrupt and permanent changes of photospheric magnetic field in the localized regions of active regions during solar flares called magnetic imprints (MIs), have been observed for the past nearly three decades. The well known "coronal implosion" model is assumed to explain such flare associated changes but the complete physical understanding is still missing and debatable. In this study, we made a systematic analysis of flare-related changes of photospheric magnetic field during 21 flares (14 eruptive and 7 non-eruptive) using the high-cadence (\texttt{135s}) vector-magnetogram data obtained from Helioseismic and Magnetic Imager. The MI regions for eruptive flares are found to be strongly localised, whereas the majority of non-eruptive events ($>70~\%$) have scattered imprint regions. To quantify the strength of the MIs, we derived the integrated change of horizontal field and total change of Lorentz force over an area. These quantities correlate well with the flare strength, irrespective of whether flares being eruptive or not, short or long duration. Further, the free-energy (FE), determined from virial-theorem estimates, exhibits statistically significant downward trend which starts around the flare time is observed in majority of flares. The change of FE during flares do not depend on eruptivity but have a strong positive correlation ($\approx 0.8$) with the Lorentz force change, indicating that the part of FE released would penetrate into the photosphere. While these results strongly favor the idea of significant feedback from corona on the photospheric magnetic field, the characteristics of MIs are quite indistinguishable for flares being eruptive or not.