Eruptions and Equilibria in the
Solar Corona

Abstract

The dynamic behaviour of the Solar Corona is dominated by its magnetic field.
Complex magnetic structures can form in the corona which have the potential to
catastrophically erupt, releasing vast amounts of energy in the form of coronal mass
ejections – eruptions which can ultimately result in increased space weather activity. This thesis discusses a variety of numerical methods used to model the coronal
magnetic field, including new approaches and techniques that could theoretically be
used to improve space weather predictions.
The thesis consists of three relatively unconnected chapters. We first describe a
new magnetic field model which calculates a magnetofrictional equilibrium with an
imposed solar wind profile. These ‘outflow fields’ appear to approximate the real
coronal magnetic field more closely than the established potential field model, take
a similar time to compute, and avoid the need to impose an artificial source surface.
Including the solar wind tends to increase the open magnetic flux compared to a
potential field, reducing the well known discrepancy with in situ observations.
These equilibrium fields can be used as initial conditions for the bulk of our research,
which is the application of both magnetofrictional and MHD models to investigate
which quantity or quantities can best predict the loss of equilibrium of magnetic
flux ropes – one of the primary mechanisms behind coronal mass ejections. Using
a very large parameter study in 2.5D, we find that in our models eruptions can be
predicted reliably using certain ratios between measurable diagnostic quantities.
We finish the thesis by describing in detail the development of a brand-new magnetofrictional model, based on an icosahedral grid. Although we have not yet used
this code to its full potential, preliminary tests indicate that this new model could
be useful in future simulations involving the prediction of magnetic flux rope eruptions