Solar influences in the heliosphere: understanding coronal mass ejections and their associated magnetic clouds

Coronal mass ejections (CMEs) are large-scale explosions on the Sun that expel plasma and magnetic field into the heliosphere. The interplanetary counterparts of CMEs, termed interplanetary CMEs (ICMEs), are often directly observed by spacecraft located in the near-Earth environment, and this thesis focuses on understanding the evolution of these structures as the propagate away from the Sun and into the heliosphere. This work contributes to the understanding of space weather in the near-Earth environment, which is known to affect the technological systems at Earth upon which we increasingly rely. A subset of ICMEs, termed magnetic clouds, in which a flux rope structure can often be identified, form the primary focus of these studies. The process by which a magnetic cloud observed directly in interplanetary space may be linked with its associated CME, through the combined study of remote observations of the Sun and in situ observations near-Earth, is discussed. A comparison of the magnetic topology of the erupting structure at both the Sun and in interplanetary space allows us to infer the process by which it erupts, and better understand its evolution as it propagates through the heliosphere. A subset of magnetic clouds, in which we directly observe unusual internal substructure, is identified. We examine the physical nature of this substructure, characterising the observed behaviour of both the magnetic field and plasma in these regions. To improve our understanding of the external physical processes that influence the evolution of a magnetic cloud in interplanetary space, we investigate, and ultimately evaluate, a number of physical mechanisms that may lead to the formation of unusual magnetic cloud topology