Authors: Momchil Molnar (Southwest Research Institute), Roberto Casini (NSF NCAR/HAO), Bibhuti Jha (Southwest Research Institute), Yuhong Fan (NSF NCAR/HAO), Chloe Pistelli (University of Montana), Giuliana de Toma (NSF NCAR/HAO)

Space-weather forecasting requires knowledge of the CME magnetic field strength, orientation, and topology before they reach Earth. However, coronal fields are weak, and Zeeman-induced circular polarization in the corona is often too small for routine CME magnetometry. The He I 1083 nm triplet provides a promising alternative, as cool prominence material entrained in CMEs remains observable while its linear polarization is sensitive to magnetic fields through the unsaturated Hanle effect. We investigate He I 1083 nm spectropolarimetry as a diagnostic of CME magnetic structure using forward modeling from realistic MHD prominence-eruption simulations The models show that the He I 1083 nm linear-polarization morphology is linked to the topology of the erupting flux rope, while multi-vantage observations can help reduce some of the Hanle ambiguities. Recent UCoMP results demonstrate the feasibility of this approach, detecting eruptive prominence material to nearly 2 solar radii and providing complementary line-of-sight velocity information. These results support He I 1083 nm spectropolarimetry as a path toward earlier, magnetically informed CME characterization for space-weather forecasting.