The flux rope nature of coronal mass ejections

Coronal mass ejections (CMEs) are ejections of magnetized plasma from the solar corona. They are the most spectacular examples of explosive energy release on the Sun. Their magnetic structure is of particular importance because it determines their effects on the terrestrial magnetosphere. Here, I present recent observational evidence for the existence of magnetic flux ropes within CMEs. The observations detect the formation of the flux rope in the low corona, reveal its sometimes extremely fast evolution and follow it into interplanetary space. The results validate many of the expectations of the CME initiation theories. We can now construct a coherent picture of the eruption of helical fields from the solar corona but some of the details remain obscure. (paper)