Speaker
Description
Coronal mass ejections (CMEs) are still modelled as isolated, highly twisted, circular flux ropes, a picture that forms the basis of many reconstruction methods and much of present-day space-weather work but that no longer matches the magnetic complexity revealed by recent data and simulations. In this talk, in situ and multi-spacecraft measurements, remote observations, and numerical modelling will be brought together with topological tools to outline a more realistic view of CME magnetic structure and its evolution from the low corona to 1 au and beyond. Observational constraints on twist, writhe, open–closed connectivity, aspect ratios, and coherence will be summarized, and particular attention will be paid to where they conflict with the classical, cylindrically symmetric, force-free flux-rope picture. A helicity-based framework will then be outlined in which CME structure is described in terms of self (twist and writhe) and mutual helicity between multiple flux systems, with winding numbers evaluated from 3-D simulations propagated to 1 au. For a representative simulated Sun–Earth CME, the total helicity is found to receive substantial contributions from twist, writhe, and mutual helicity between distinct flux regions, with mutual helicity accounting for a significant fraction of the total and writhe being of the same order as twist within the core flux rope. Taken together, these findings are interpreted as indicating that standard 1-D in situ fitting tends to overemphasize twist, that CME structures consistent with the observations need not be strongly twisted, and that forecasting and Sun–heliosphere coupling studies should explicitly account for writhe, mutual helicity, and the coexistence of open and closed field lines within the ejecta