Observational Evidence of Back-reaction on the Solar Surface Associated with Coronal Magnetic Restructuring in Solar Eruptions

TL;DR

This study provides observational evidence that solar eruptions induce rapid, irreversible changes in photospheric magnetic fields, supporting models where coronal magnetic restructuring influences the photosphere during flares.

Contribution

It synthesizes previous research and new observations to demonstrate how photospheric magnetic fields respond to coronal magnetic reconnection during solar eruptions.

Findings

Transverse magnetic field increases at the polarity inversion line during flares.

Magnetic flux in flaring regions shows rapid, irreversible changes post-eruption.

Most observed flux changes support the theory of coronal field restructuring affecting the photosphere.

Abstract

Most models of solar eruptions assume that coronal field lines are anchored in the dense photosphere and thus the photospheric magnetic fields would not have rapid, irreversible changes associated with eruptions resulted from the coronal magnetic reconnection. Motivated by the recent work of Hudson, Fisher & Welsch (2008) on quantitatively evaluating the back reaction due to energy release from the coronal fields, in this Letter we synthesize our previous studies and present analysis of new events about flare-related changes of photospheric magnetic fields. For the 11 X-class flares where vector magnetograms are available, we always find an increase of transverse field at the polarity inversion line (PIL) although only 4 events had measurements with 1 minute temporal resolution. We also discuss 18 events with 1 minute cadence line-of-sight magnetogram observation, which all show prominent changes of magnetic flux contained in the flaring Delta spot region. Except in one case, the observed limb-ward flux increases while disk-ward flux decreases rapidly and irreversibly after flares. This observational evidence provides support, either directly or indirectly, for the theory and prediction of Hudson, Fisher & Welsch that the photospheric magnetic fields must respond to coronal field restructuring and turn to a more horizontal state near the PIL after eruptions.