Yardley, SL; (2017) The role of flux cancellation in the formation of filaments and eruptive structures. Doctoral thesis , UCL (University College London).

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Abstract

The work conducted in this thesis represents a contribution towards understanding the important processes involved in the formation of filaments and eruptive structures in the solar atmosphere. In particular, the role that ongoing photospheric flux cancellation and associated magnetic reconnection plays in the origin of filament plasma. Also, to study how the magnetic field configuration evolves as flux cancellation proceeds to find indications of the onset of filament eruptions as coronal mass ejections (CMEs). This process is capable of re-configuring the supporting magnetic field from a sheared coronal arcade to a flux rope configuration, building up non-potential field in the atmosphere and storing free magnetic energy along the polarity inversion line. These helical configurations consist of concave-up sections or magnetic dips that provide locations for filament material to be supported against gravity. Flux cancellation observations, whereby small-scale opposite polarity features converge, collide and subsequently dis- appear in line-of-sight magnetic field can therefore, provide a way to investigate how much magnetic flux has been built into the magnetic field configuration that contains the filament before eruption. This process is crucial to the understanding of the onset of CMEs. In this thesis, a small sub-set of active regions have been studied. Observations of the photospheric field have been used to study the field evolution of active regions and its relationship to eruptions. To study the magnetic evolution of these regions an automated algorithm has been developed which tracks magnetic features in line-of-sight magnetic field data to calculate the total quantity and rate of flux cancellation. Chromospheric and coronal plasma observations have been used to study the presence of filament material and plasma flows, in relation to flux cancellation sites. Finally, these observations have been compared to the field configuration and locations of magnetic dips present in non-linear force-free field models.

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