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Issue A&A Volume 378, Number 1, October IV 2001 Page(s) 239 - 246 Section The Sun DOI 10.1051/0004-6361:20011170

A&A 378, 239-246 (2001)
DOI: 10.1051/0004-6361:20011170

Long term evolution of a non-active region sigmoid and its CME activity

A. Glover, L. K. Harra, S. A. Matthews, K. Hori and J. L. Culhane

Mullard Space Scence Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
    e-mail: lkh@mssl.ucl.ac.uk; sam@mssl.ucl.ac.uk; kh@mssl.ucl.ac.uk; jlc@mssl.ucl.ac.uk

(Received 14 March 2001 / Accepted 3 August 2001 )

Abstract
Recent studies have considered sigmoidal features in the Solar corona to possess a high probability of eruption. Unlike these studies which have focussed only on active region sigmoids, the present work centres on a large area which developed S-like morphology unconfined by a single active region. The S-like feature formed near the central meridian on 8th May 2000 and was observed to erupt, with an associated CME, twice over a period of 3 days. We observe considerable CME and flaring activity in two previous rotations, consistent with the observation of active regions and emerging flux. We illustrate sigmoid formation through the appearance of highly sheared soft X-ray loops overlying an extended filament channel. This arises from the gradual diffusion of flux associated with a large, dispersing active region over the period of three solar rotations. This scenario is indicative of shear build-up within the region over several rotations. The observed CMEs act to remove helicity from the highly sheared sigmoidal feature, finally producing an approximately potential filament channel on 10th May 2000.

Key words: sigmoid -- Coronal Mass Ejection -- flare -- helicity

Offprint request: A. Glover, ahg@mssl.ucl.ac.uk

© ESO 2001

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