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Coronal Plasma Composition Evolution and Solar Activity

To, Andy Shu Ho; (2023) Coronal Plasma Composition Evolution and Solar Activity. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

Composition of plasma in the solar corona is a tracer of the flow of plasma and energy from the solar interior. A complete understanding of coronal abundances not only provides us with another perspective to look at complex processes such as wave propagation, wave absorption, convection, reconnection, and reconfiguration of magnetic fields and coronal heating, but it also has significant implications for solar-like stars. The method to parameterise and study coronal elemental abundances, is to use the first ionisation potential (FIP) bias, defined as taking the ratio of an element’s coronal to photospheric abundances with respect to H. In this thesis, I introduce FIP bias as a proxy to understand processes in different solar structures and events, ranging from transient events such as small brightenings and big flares, to more stable structures such as active regions, and extend it to insights on solar activity. I use spatially resolved solar observations to quantify and interpret the composition changes in these events and solar structure. In particular, I compare for the first time, the composition evolution of a small flare using two pairs of composition diagnostics. The result shows that the abundances of different high-FIP elements can have distinct behaviour, depending on the heating and the chromospheric environment of an event. Furthermore, by combining JVLA F10.7 flux and EIS composition observations, I show that magnetic flux density plays a key role in the composition saturation effect. Locally, this saturation is often observed in leading sunspots, where magnetic flux is more concentrated. Globally, this saturation effect can be observed when the solar activity is at its maximum, and also in stellar coronae. The results indicate the importance of solar observations to understand stellar atmospheres. Finally, I investigate the long term spatially resolved composition evolution of the famous 10 September 2017 X-class flare. The results show that composition can be used to indicate plasma flows in flares, and suggest that spatially resolved observations are crucial to understand composition changes in flares.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Coronal Plasma Composition Evolution and Solar Activity
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Copyright © The Author 2023. 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
UCL > Provost and Vice Provost Offices > UCL BEAMS
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 Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10175774
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