Coronal mass ejections

While the first coronal mass ejections (CMEs) were observed with the OSO‐7 white light coronagraph (Tousey, 1973), it was the Skylab coronagraph observations that clearly established CMEs as an important component of solar coronal physics. CMEs have been defined by Hundhausen et al. (1984a) as observable changes in coronal structures occurring on time scales of minutes to hours and involving new, discrete bright features in the field of view. Although only a fraction of all observed coronal activity, CMEs are of interest because they involve discrete additions of mass and magnetic fields to the solar wind. These large coherent structures, observed to expand to many times the diameter of the sun as they moved outward into interplanetary space, not only provided a fascinating new phenomenon for study, but were also perceived as the “missing link” between solar flares and geomagnetic storms (Hundhausen et al., 1984b).