The Evolution of Interplanetary Coronal Mass Ejections in the Heliosphere
File(s)
Author(s)
Davies, Emma
Type
Thesis
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.
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.
Version
Open Access
Date Issued
2021-05
Date Awarded
2021-08
Copyright Statement
Creative Commons Attribution NonCommercial NoDerivatives Licence
Advisor
Forsyth, Robert
Sponsor
Science and Technology Facilities Council (Great Britain)
Grant Number
ST/N504336/1
Publisher Department
Physics
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)