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Coronal mass ejections (CMEs) are solar eruptions. Strong magnetic fields in active regions (ARs) make CMEs inevitable, driven by stored energy and helicity, leading to flux ropes and space weather impacts.

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Area of Science:

  • Solar physics
  • Heliophysics
  • Space weather

Background:

  • Coronal mass ejections (CMEs) are large expulsions of plasma and magnetic field from the Sun's corona.
  • Observing CMEs requires coronagraphs, necessitating complementary disc observations (EUV, X-rays, Halpha, radio) to study their origins.

Purpose of the Study:

  • To review key properties of CME source regions.
  • To highlight a causal sequence of events leading to CMEs in eruptive active regions (ARs).
  • To describe the pre-eruptive phase of CMEs, particularly those with significant space weather implications.

Main Methods:

  • Review of existing literature on CME sources and their development.
  • Analysis of the role of magnetic polarity inversion lines in active regions.
  • Focus on the accumulation of magnetic energy and helicity.

Main Results:

  • Strong, sheared magnetic polarity inversion lines in ARs efficiently store energy and helicity, making eruptions inevitable.
  • These conditions favor the formation of pre-eruptive magnetic flux ropes.
  • A plausible causal sequence for the pre-eruptive phase is outlined, applicable to most CMEs.

Conclusions:

  • Eruptive ARs with strong magnetic configurations follow an irreversible path toward CMEs once energy and helicity thresholds are crossed.
  • Understanding the pre-eruptive phase is crucial for predicting CMEs and their space weather impacts.
  • The reviewed sequence provides a framework for studying high-energy CMEs with significant space weather consequences.