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Article Dans Une Revue Solar Physics Année : 2009

Evidence of Magnetic Helicity in Emerging Flux and Associated Flare

Résumé

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 multiwavelength analysis of an M1.6 flare occurring in the NOAA active region 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 Halpha by the MSDP spectrograph in the Meudon solar tower and in 1600 Å 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 has been 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 is 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.

Dates et versions

hal-03732778 , version 1 (21-07-2022)

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Ramesh Chandra, Brigitte Schmieder, Guillaume Aulanier, Jean-Marie Malherbe. Evidence of Magnetic Helicity in Emerging Flux and Associated Flare. Solar Physics, 2009, 258, pp.53-67. ⟨10.1007/s11207-009-9392-z⟩. ⟨hal-03732778⟩
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