Solar active region energetics, magnetic polarity mixing and their relation to flares

Solar flares are among the most energetic events in the solar system, affecting physical systems from the solar surface to the heliosphere, geo-space and beyond. Flares, alongside coronal mass ejections (CMEs), are major contributors to space weather - changing conditions in the near-Earth space, magnetosphere and upper atmosphere. Flares mostly occur in active regions; parts of the solar atmosphere dominated by magnetic field. Flows move field around and, after enough energy accumulates and conditions are suitable, active regions can release free energy as flares/CMEs.

Free energy stored by the magnetic field can be obtained from (computationally expensive) non-linear force-free field (NLFFF) extrapolations and is known to be sufficient to power flares/CMEs. However, the conditions required to initiate these events are unclear, limiting our ability to forecast them. The main forms of active region energy injection are known to be emergence of magnetic field through the solar surface and horizontal flows acting on previously emerged field, but we lack quantitative understanding of the contributions these injection processes provide to active region flaring/eruption energy budgets. Twisted magnetic field in active region atmospheres indicate that the field holds free energy, and directly relates to the complexity of magnetic-polarity spatial mixing on the surface. Quantifying the degree of polarity mixing and its relation to NLFFF-extrapolated energy budgets will provide a novel, computationally inexpensive free-energy proxy that has not previously been considered, while studying the motion/evolution of polarities in active regions will shed light on flare triggers. This project concerns the magnetic conditions that power and initiate flares, with the potential to impact on the quality/timeliness of adverse space weather forecasting and increasing the operational capacity of space-weather forecast centres (e.g., UK Met Office).

This project aims to understand the roles that energy injection/storage and polarity mixing play in the production of flares in active regions, before utilizing this knowledge to develop new machine-learning flare forecasting schemes. The study of active region magnetic energy is dominated by case studies, but this work will provide a step change in understanding active region energetics by considering a large statistical sample. The aim will be achieved by:

1) investigating the contributions of flux emergence and surface flows to magnetic energy evolution in flaring and non-flaring active regions;

2) developing new measures to quantify the degree of magnetic-polarity mixing;

3) examining the relation of flaring to energy injection/storage, polarity mixing, and motion/evolution of polarities within active regions;

4) implementing machine-learning schemes to forecast flares using these measures/behaviours and quantifying their performance using verification metrics.