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The Evolution of Interplanetary Coronal Mass Ejections in the Heliosphere

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Title: The Evolution of Interplanetary Coronal Mass Ejections in the Heliosphere
Authors: Davies, Emma
Item Type: Thesis or dissertation
Abstract: Interplanetary coronal mass ejections (ICMEs) are large scale structures of plasma and magnetic field that are driven from the solar atmosphere and propagate through the heliosphere. ICMEs are the main drivers of strong geomagnetic activity at Earth, thus understanding their evolution is important in space weather forecasting. Our best knowledge of ICME evolution beyond 1 AU comes from the Ulysses mission, launched in 1990 and decommissioned in 2009. The cruise phase of the Juno mission to Jupiter provides the most recent opportunity to study ICMEs between 1 and 5.4 AU. In this thesis, ICMEs identified in the Juno magnetic field dataset have been catalogued and analysed. The inclination of magnetic flux ropes was found to decrease with increasing heliocentric distance, perhaps a suggestion of ICME deflection and rotation towards the ecliptic plane continuing beyond 1 AU. The mean magnetic field strength of the flux ropes was found to decrease with heliocentric distance, in agreement with previous studies conducted using Ulysses data. 11 of the catalogued events were also observed by other spacecraft situated at a heliocentric distance of 1 AU or below, allowing for a wider multi-spacecraft study to be conducted and forming the basis for more detailed case studies. In one such case study, significant differences were found between observations and event properties at different spacecraft despite the small longitudinal separation, demonstrating that caution should be exercised in radial alignment studies and the importance of taking the solar wind background into consideration when analysing ICMEs. A comparison of two separate isolated ICMEs was conducted, one occurring during solar maximum and the other at solar minimum. A clear deformation of the ICME observed at solar minimum is observed, likely due to the highly structured solar wind environment through which it propagated. Neither ICME was found to expand self-similarly as one would expect if we consider the magnetic flux ropes to be cylindrical and force-free, which may have important implications for space weather modelling.
Content Version: Open Access
Issue Date: May-2021
Date Awarded: Aug-2021
URI: http://hdl.handle.net/10044/1/91934
DOI: https://doi.org/10.25560/91934
Copyright Statement: Creative Commons Attribution NonCommercial NoDerivatives Licence
Supervisor: Forsyth, Robert
Sponsor/Funder: Science and Technology Facilities Council (Great Britain)
Funder's Grant Number: ST/N504336/1
Department: Physics
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Physics PhD theses

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