Coronal mass ejections, magnetic flux ropes, and solar magnetism

This review on coronal mass ejections (CMEs) treats hydromagnetic issues posed by observations, in order to relate CMEs to flares and prominence eruptions and to consider the roles these processes play in the evolution of the solar corona in the course of an 11-year cycle. This global view of the corona, proposed in varying degrees of completeness by the author, physically connects the corona to the photosphere and the dynamo in the solar interior. This view is synthesized afresh starting with CME phenomenology, in order to include some new insights and to arrive at definite statements on the hydromagnetic nature of CMEs. The synthesis shows that each CME culminates a long, coherent physical process involving magnetic-flux emergence; flares and magnetic reconnection; creation of long-lived, large-scale coronal structures; conservation of magnetic helicity; and failure of confinement of magnetic flux ropes in the open atmosphere. Each CME contributes a systematic permanent change to the coronal magnetic field. In this view the cumulative changes brought by all the CMEs in the course of a solar cycle have fundamental implications for the magnetic-flux budgets of the photosphere and the corona.