Multi-Spacecraft Investigations of Solar and Interplanetary Coronal Mass Ejections in Complex Solar Wind Environments

Abstract

Coronal Mass Ejections (CMEs) are large, dynamically evolving structures of plasma and magnetic fields ejected from the Sun's atmosphere, the corona. As they propagate outward from the Sun into the heliosphere, they are observed in situ as Interplanetary Coronal Mass Ejections (ICMEs). ICMEs are the biggest drivers of space weather throughout the heliosphere, the study of how the Sun’s activity affects us on Earth, in our near-space environment, and on other planets.

In this thesis, we develop and explore concepts to better understand the kinematic, geometric, magnetic, and thermodynamic properties of (I)CME evolution, propagation, and expansion. We aim to explore local and global (I)CME properties, (I)CME propagation dynamics, and CME - ICME connection signatures.

We use a variety of remote sensing and in situ data from the Ulysses, twin-STEREO, ACE, and SOHO spacecraft, applying both single and multi-spacecraft methods to analyse (I)CMEs. We present a review of multi-spacecraft findings and techniques relevant to understanding (I)CME observations and development using multi-spacecraft techniques to date. We discuss the limitations of remote sensing and in situ observations and how they may be mitigated with multi-spacecraft techniques.

We present two single-event studies: first, a combined study of a CME revealed in a unique orbital configuration which permits the analysis of remote-sensing observations from the twin STEREO -A and -B spacecraft and of its subsequent in situ counterpart outside the ecliptic plane, the ICME observed by Ulysses. This study explores how the local solar wind environment impact (I)CME expansion, evolution, and propagation. Second, a study of an ICME observed in situ near the ecliptic embedded in a co-rotating interaction region using remote-sensing and in-situ observations using the twin-STEREO, and ACE spacecraft with complementary methods of analysis and compare it with the (I)CME observed at Ulysses, which explores the local versus global ICME structures in the context of different solar wind environments across different latitudes.

We investigate the properties of (I)CME expansion through two multi-event studies. In the first study, we investigate the thermodynamic properties of ICMEs and aim to explore how this impacts ICME expansion as they propagate through the solar wind. Here we explore how the magnetic structures of CMEs evolve from launch and through to development into an ICME and if the drivers of CME expansion in the corona are the same as that in the heliosphere. In the second study, we consider how the magnetic structure of CMEs evolve by considering CMEs from bi-polar active regions.

We present a discussion of open questions on (I)CME evolution and expansion, highlight relevant findings, the scope for future work, and a summary of the work presented. We conclude that there are many open questions pertaining to (I)CME evolution and development in the corona and heliosphere. We are inclined to support the hypothesis that all (I)CMEs contain flux ropes and conclude that the local solar wind environment can significantly impact (I)CME expansion and evolution.