http://www.issibern.ch/teams/coronalprom/issipropsmall.pdf>Cavities are commonly observed as part of a CME, but may also exist beforeeruption (Sterling and Moore 2004; Gibson et al. 2006). Such quiescent cavities appear as
dark, semi-circular or circular regions, often surrounding a central prominence (relatively
cool and dense plasma suspended in the solar corona), and embedded in a helmet-shaped
white-light streamer (Figure 1, left). They are ubiquitous: several may be visible on a given
day; and can be long-lived (on the order of months): either reforming or only partly erupting
in CMEs (Gibson and Fan 2006b; Su et al. 2006; Tripathi et al. 2007, 2008).
