Coronal Manifestations of Eruptive Prominences, Observation and Interpretation

To appreciate the curious nature of the coronal manifestations of eruptive prominences, we must first recall how the corona around a quiescent prominence appears. The cool prominence material threads arcades of coronal loops, but is invisible in coronal lines. If one defines the corona as a million-degree gas above the chromosphere, then one must admit that there is no detectable corona where there is a filament. Simultaneous limb photographs in Ha and in coronal lines show that filaments outside of active regions reside in dark cavities in the corona. Active region filament cavities would be difficult to see because of the compact loop systems that characterize the corona there, but extrapolating from our experience with non-active region filaments, we can say, at least, that the loop arcade pattern inside active regions is the same as outside and that there is no evidence for any high-temperature, filament-shaped features in active regions.