Whitepaper #127 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: basic research. Additional topics: ground-based missions/projects; solar physics; space-based missions/projects; user-need-driven basic space weather research.
The mechanism for the release of stored magnetic energy in solar eruptions remains a major unsolved problem of Heliophysics. Choosing between triggers requires knowledge of pre-eruptive magnetic fields. Current coronal observations are insufficient to diagnose 3D coronal magnetic fields in CME precursors, motivating recommendations for new capabilities in next-generation V/IR and UV telescopes.