Fields and flares : understanding the complex magnetic topologies of solar active regions

Abstract

Sunspots are regions of decreased brightness on the visible surface of the Sun (photosphere) that are associated with strong magnetic fields. They have been found to be locations associated with solar flares, which occur when energy stored in sunspot magnetic fields is suddenly released. The processes involved in flaring and the link between sunspot magnetic fields and flares is still not fully understood, and this thesis aims to gain a better understanding of these topics. The magnetic field evolution of a number of sunspot regions is examined using high spatial resolution data from the Hinode spacecraft. Photospheric magnetic field data is first investigated, and significant increases in negative vertical field strength, negative vertical current density, and field inclination angle towards the vertical are observed just hours before a flare occurs, which is on much shorter timescales than previously studied. These parameters then return to their pre-are ‘quiet’ state after the flare has ended. First observations of spatial changes in field inclination across a magnetic neutral line (generally believed to be a typical source region of flares) are also discovered. The changes in field inclination observed in this thesis confirm field configuration changes due to flares predicted by a number of previous works. 3D magnetic field extrapolation methods are then used to study the coronal magnetic field, using the photospheric magnetic field data as a boundary condition. Significant geometrical differences are found to exist between different field configurations obtained from three types of extrapolation procedure (potential, linear force free, and non-linear force free). Magnetic energy and free magnetic energy are observed to increase significantly a few hours before a are, and decrease afterwards, which is a similar trend to the photospheric field parameter changes observed. Evidence of partial Taylor relaxation is also detected after a are, as predicted by several previous studies. The research presented in this thesis gives insight into photospheric and coronal magnetic field evolution of flaring regions. The magnetic field changes observed only hours before a flare could be useful for are forecasting. Field changes observed due to the flare itself have confirmed currently proposed magnetic field topology changes due to flares. The results outlined show that this particular field of research is vital in furthering our understanding of the magnetic nature of sunspots and its link to are processes.