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

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

Corresponding author: A. Glover, ahg@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.