Glover, Alexandra Hannah; (2003) The association of sigmoidal features and transequatorial interconnecting loops with eruptive solar activity. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis examines sigmoidal solar X-ray features and transequatorial-interconnecting loops. Recent studies have suggested that both features exhibit a high probability of eruption to produce a coronal mass ejection (CME). The thesis begins with an introduction to the solar atmosphere and the physics governing its behaviour. The physics involved in flaring and CME onset will then be introduced and difficulties in our understanding of the relationship between these events highlighted. Solar instrumentation and data analysis techniques used throughout this thesis is also introduced together with a discussion of capabilities and limitations. Although many authors have referred to 'sigmoidal' features in the corona, observations have not yet confirmed the nature of such features. Sigmoidal active regions previously observed using Yohkoh/SXT alone form the basis of a multi-wavelength study incorporating SOHO/LASCO, EIT and MDI observations, together with ground-based H-alpha data. Regions previously classified as 'sigmoidal' are frequently found to comprise several shorter loops, the overall projection of which appears to form a single S (or reverse-S) shaped feature. An example of a non-active region sigmoid is studied in terms of its morphology, CME and flaring activity over three solar rotations. This study is the first to consider a sigmoidal feature unconfined by a single active region in detail. The region's flaring and CME activity is studied and the relative timing of eruptive activity and sigmoid appearance is considered. Previous studies have shown transequatorial loop systems (TLS), connecting active regions in opposite hemispheres to disappear in association with CME onset. This thesis describes a number of TLS in terms of their formation, morphology and associated CME and flaring activity. TLS are found to exhibit a variety of responses to CME onset including both brightening and dimming. Loops extending over a wide range in latitude appear more likely to be associated with CME onset.

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