Mihailescu, Alexandra Teodora; (2024) Drivers and Effects of Plasma Composition Variations in the Solar Corona. Doctoral thesis (Ph.D), UCL (University College London).

Text Alexandra Teodora Mihailescu - PhD Thesis (final version).pdf - Other Access restricted to UCL open access staff until 1 August 2025. Download (70MB)

Abstract

The plasma composition of the solar corona is characterised by an overabundance of elements with a low first ionization potential (FIP) compared to those with a high FIP. This enhancement of low-FIP elements is believed to take place in the chromosphere and is characterised by the FIP bias parameter. The aim of the research outlined in this thesis is to understand this universal process on large and small spatial scales, long and short timescales, and quiescent and flaring conditions using spectroscopic observations in the extreme ultraviolet range. First, the FIP bias dependence on magnetic activity was investigated in quiescent active regions over large scales and timescales of weeks to months. Results indicate a correlation between FIP bias and magnetic flux density. The active regions in the study display a wide range of FIP bias values which change with the active region evolutionary stage suggesting that sub-active region processes can influence the FIP bias in different ways. Next, the link between plasma composition patterns at sub-active region level and Alfvén wave activity over timescales of a few hours was explored in more detail. Matching spectroscopic observations with predictions from simulations of the FIP effect suggests that the plasma composition pattern observed in a coronal loop depends on the properties of the Alfvén waves driving the enhancement and, particularly, the chromospheric height at which they deposit their energy. Finally, this work was extended to dynamic processes with timescales of seconds to minutes by studying the evolution of plasma composition in an M-class solar flare. The strong heating and associated plasma flows change the plasma composition of the flare loops which, in turn, influences the radiative cooling process of the loops. Observations suggest high/low FIP bias and faster/slower cooling at the top/footpoint of the loop, in agreement with predictions of the radiative cooling process. The overall conclusion of this thesis is that plasma composition in the solar corona is tightly linked to other processes such as magnetic activity, heating, Alfvén wave activity and radiative cooling.

Download activity - last month

Export as JSONXMLCSV

Download activity - last 12 months

Export as JSONXMLCSV

Downloads by country - last 12 months

Export as JSONCSVXML

Archive Staff Only

View Item