Active Prominences

Those prominences which are identified as active lie near the middle of a large group of objects found in the low corona bordered on the high energy side by flares and on the low energy side by quiescent prominences. Known by descriptive terms such as eruptive, surge, spray, tornado, and loop, active prominences typically have shorter lifetimes, broader line widths, larger internal motions, and stronger internal magnetic fields than quiescent prominences (Tandberg-Hanssen, 1974). When dealing with specific examples, however, it is often difficult to establish a necessary and sufficient condition for classification of such an object as an active prominence. The ambiguity at the low energy end involves “hybrid” objects which possess features of both quiescent and active prominences. For example, the active region filament may have a lifetime of several days, have large internal motions and relatively strong magnetic fields. The stable hedgerow quiescent prominence may contain small regions with large widths and large velocities. On the average, a quiescent will typically erupt every five to eight days, (Serio, et al., 1978; Bryson and Malville, 1978) and at those times a prominence is transformed from the quiescent to the active state. For these objects something other than morphology, velocity fields, or even magnetic fields is necessary to specify their condition; something less symptomatic and more fundamental is required. That necessary parameter may be, I shall suggest, the total current, J, flowing in the structure.