Evidence of Magnetic Helicity in Emerging Flux and Associated Flare

TL;DR

This study demonstrates that magnetic helicity signs in emerging flux regions are consistent with flare signatures, providing observational evidence linking flux emergence and flare activity in solar active regions.

Contribution

It presents the first clear observational correlation between magnetic helicity in emerging flux and associated flare ribbons, supporting models of flux emergence and flare triggering.

Findings

Magnetic tongues indicate positive helicity in emerging flux.

Flare ribbons exhibit 'J' shapes consistent with magnetic reconnection.

Coronal null points are associated with secondary brightenings.

Abstract

The aim of this paper is to look at the magnetic helicity structure of an emerging active region and show that both emergence and flaring signatures are consistent with a same sign for magnetic helicity. We present a multi-wavelength analysis of an M1.6 flare occurring in the active region NOAA 10365 on 27 May, 2003, in which a large new bipole emerges in a decaying active region. The diverging flow pattern and the "tongue" shape of the magnetic field in the photosphere with elongated polarities are highly suggestive of the emergence of a twisted flux tube. The orientation of these tongues indicates the emergence of a flux tube with a right hand twist, i.e. positive magnetic helicity. The flare signatures in the chromosphere are ribbons observed in H-alpha by the MSDP spectrograph in the Meudon solar tower and in 1600 A by TRACE. These ribbons have a `J' shape and are shifted along the inversion line. The pattern of these ribbons suggests that the flare was triggered by magnetic reconnection at coronal heights below a twisted flux tube of positive helicity, corresponding to that of the observed emergence. It is the first time that such a consistency between the signatures of the emerging flux through the photosphere and flare ribbons is clearly identified in observations. Another type of ribbons observed during the flare at the periphery of the active region by the MSDP and SOHO/EIT are related to the existence of a null point, which is found high in the corona in a potential field extrapolation. We discuss the interpretation of these secondary brightenings in terms of the "breakout" model and in terms of plasma compression/heating within large-scale separatrices.