French, Ryan James;
(2022)
Spectroscopic and Spectropolarimetric Insights into Reconnection Dynamics in Solar Flares.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Solar flares are one of the most energetic events in the solar system, created by the explosive conversion of magnetic free energy into particle acceleration, plasma heating and EM radiation through the process of magnetic reconnection. It is believed that in solar flares, magnetic reconnection occurs within a current sheet between converging oppositely-orientated magnetic fields – but the nature of reconnection and exact mechanisms behind the release and transport of energy within flares are still uncertain. Current sheets are notoriously difficult to observe, primarily due to their small thickness (below current observable limits of instrumentation). Sometimes, hot plasma sheets can be seen along suspected current sheet regions during off-limb flares, but such events are uncommon and rarely caught in spectroscopic observations. One such X-class flare occurred on the 10th September 2017. In the first two science chapters of this thesis, a range of space and ground-based instrumentation are used to study the nature of reconnection dynamics in this 10th September 2017 event. Primarily, we compare infrared linear polarisation data from the Coronal Multi-channel Polarimeter instrument with simple empirical models, to find evidence for magnetic structure on sub-pixel scales. The results are compatible with the ‘tearing mode instability’ model of reconnection. Taking this analysis further, we use extreme-ultraviolet spectroscopy with the Hinode Extreme-Ultraviolet Imaging Spectrometer (and other supporting instruments) to explore the long duration over which reconnection and energy release persists in this event. However, we cannot always rely on rare off-limb events to further our knowledge of flare reconnection dynamics. In the third science chapter, Fast Fourier Transforms along flare ribbons of a small flare reveal insight into the growth of spatial scales in the current sheet region. This method reveals further evidence for the tearing mode instability triggering plasma turbulence at the onset of reconnection. Although reconnecting current sheet regions are elusive, the work in this thesis develops novel techniques to probe the nature of magnetic processes within these crucial regions. The methodology used in this thesis can be pushed further, as observations from next-generation instrumentation start to become available.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Spectroscopic and Spectropolarimetric Insights into Reconnection Dynamics in Solar Flares |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2021. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy UCL > Provost and Vice Provost Offices > UCL BEAMS UCL |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10151826 |
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