Physical processes involved in the EUV "Surge" Event of 09 May 2012

TL;DR

This study analyzes an EUV confined ejection event in active region NOAA 11476 on 09 May 2012, revealing the magnetic reconnection processes and flux cancellation driving the eruption and associated flare, using multi-wavelength observations and magnetic modeling.

Contribution

It provides a detailed interpretation of the magnetic topology and reconnection processes behind the EUV surge, emphasizing flux cancellation and bipole rotation as key drivers.

Findings

Eruption linked to two reconnection processes, below and above the minifilament.

Magnetic flux cancellation and bipole rotation trigger homologous events.

Reconnection at quasi-separatrix layers explains the surge morphology.

Abstract

We study an EUV confined ejection observed on 09 May 2012 in active region (AR) NOAA 11476. For the analysis we use observations in multiple wavelengths (EUV, X-rays, H$\alpha$, and magnetograms) from a variety of ground-based and space instruments. The magnetic configuration showed the presence of two rotating bipoles, with decreasing magnetic flux, within the following polarity of the AR. This evolution was present along some tens of hours before the studied event and continued even later. A minifilament with a length of $\approx 30 \arcsec$ lay along the photospheric inversion line of the largest bipole. The minifilament was observed to erupt accompanied by an M4.7 flare (SOL20120509T12:23:00). Consequently, dense material, as well as twist, was injected along closed loops in the form of a very broad ejection whose morphology resembles that of typical H$\alpha$ surges. We conclude that the flare and eruption can be explained as due to two reconnection processes, one occurring below the erupting minifilament and another one above it. This second process injects the minifilament plasma within the reconnected closed loops linking the main AR polarities. Analyzing the magnetic topology using a force-free model of the coronal field, we identify the location of quasi-separatix layers (QSLs), where reconnection is prone to occur, and present a detailed interpretation of the chromospheric and coronal eruption observations. In particular, this event, contrary to what has been proposed in several models explaining surges and/or jets, is not originated by magnetic flux emergence but by magnetic flux cancellation accompanied by the rotation of the bipoles. In fact, the conjunction of these two processes, flux cancellation and bipole rotations, is at the origin of a series of events, homologous to the one we analyze in this article, that occurred in AR 11476 from 08 to 10 May 2012.