The 3D Magnetic Structure of CMEs throughout the Extended Solar Corona

The magnetic fields that make up the internal structure of coronal mass ejections (CMEs) are thought to be organised in a flux-rope configuration consisting of twisted magnetic fields that wind about a central axis. Remote-sensing observations of CMEs show a wide range of morphologies, dynamics, and evolution, including rotation, non-uniform expansion, deflection, and interaction with the ambient solar wind. In-situ measurements, however, typically consist of a single 1D spacecraft trajectory through a large 3D structure (or few at best), limiting our understanding of how the internal magnetic structure of a given CME may vary in time and space.

In this work, we analyse the magnetic configuration of an idealised CME during its early evolution in the range 1–30 Rs, using the Magnetohydrodynamic Algorithm Outside a Sphere (MAS) code. The initial flux rope erupts in a simplified coronal configuration, from a bipolar active region located under the streamer belt, and propagates through a uniform background solar wind. We place a fleet of synthetic spacecraft throughout the CME’s path at different combinations of heliocentric distance, latitude, and longitude. We identify and examine flux-rope signatures in the synthetic in-situ profiles, in order to characterise radial variations as well as latitudinal/longitudinal ones. We find that, even in the case of a simplified CME erupting under solar minimum-like conditions, the sampling location significantly affects the global structure that would be deduced from common flux-rope reconstruction and analysis techniques used for in-situ measurements.