Braiding of Coronal Loops and Consequences for Coronal Heating

Abstract

This thesis is inspired by one of the greatest mysteries surrounding our Sun: the coronal heating problem. Scientists have worked for decades to explain the extraordinary temperature increase which occurs as we move up through the solar atmosphere into the corona. Theories abound, including that of heating via reconnection, following the formation of current layers, which occur as the coronal field is braided by photospheric footpoint motions. In this work we designed different driving functions to act as braiding motions on a numerical photosphere, and sought to establish how each one affected overlying coronal fields. We used the concepts of topological entropy and helicity to categorise the drivers and applied them to a uniform field representing a simple coronal loop. We found that both complexity of driving and ability to inject helicity are key to the type of evolution which takes place, with direct consequences due to differences in these properties. The findings from the uniform field experiments also lend support to the idea that frequent nanoflares triggered along a loop could provide significant heating to the plasma. We then considered a field also involving parasitic polarities, creating a magnetic carpet, and attempted to find whether the same driving motions induced similar behaviour in a different environment. This research led us to challenge how we approach numerical work, and how the practical choices made in codes can drastically affect the success of a simulation. We found that one must consider carefully when choosing a numerical scheme to use, and be prepared potentially to change either elements of the project or the scheme itself.

Date of Award	2018
Original language	English
Awarding Institution	University of Dundee
Sponsors	Science and Technology Facilities Council
Supervisor	Gunnar Hornig (Supervisor) & David Pontin (Supervisor)