First Sdo /AIa Observation of Solar Prominence Formation Following an Eruption: Magnetic Dips and Sustained Condensation and Drainage

Imaging solar coronal condensation forming prominences was difficult in the past, a situation recently changed by Hinode and the Solar Dynamics Observatory (SDO). We present the first example observed with the SDO/Atmospheric Imaging Assembly, in which material gradually cools through multiple EUV channels in a transequatorial loop system that confines an earlier eruption. Nine hours later, this leads to eventual condensation at the dips of these loops, forming a moderate-size prominence of ∼1014 g, to be compared to the characteristic 1015 g mass of a coronal mass ejection (CME). The prominence mass is not static but maintained by condensation at a high estimated rate of 1010 g s−1 against a comparable, sustained drainage through numerous vertical downflow threads, such that 96% of the total condensation (∼1015 g) is drained in approximately one day. The mass condensation and drainage rates temporally correlate with the total prominence mass. The downflow velocity has a narrow Gaussian distribution with a mean of 30 km s−1, while the downward acceleration distribution has an exponential drop with a mean of ∼1/6 g☉, indicating a significant canceling of gravity, possibly by the Lorentz force. Our observations show that a macroscopically quiescent prominence is microscopically dynamic, involving the passage of a significant mass through it, maintained by a continual mass supply against a comparable mass drainage, which bears important implications for CME initiation mechanisms in which mass unloading is important.