Continuous upflows and sporadic downflows observed in active regions

Abstract

Aims: We present a study of the temporal evolution of coronal loops in active regions and its implications for the dynamics in coronal loops.
Methods: We analyzed images of the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) at multiple temperatures to detect apparent motions in the coronal loops.
Results: Quasi-periodic brightness fluctuations propagate upwards from the loop footpoint in hot emission at 1 MK, while sporadic downflows are seen in cool emission below 1 MK. The upward motion in hot emission increases just after the cool downflows.
Conclusions: The apparent propagating pattern suggests a hot upflow from the loop footpoints, and is considered to supply hot plasma into the coronal loop, but a wavelike phenomenon cannot be ruled out. Coronal condensation occasionally happens in the coronal loop, and the cool material flows down to the footpoint. Emission from cool plasma could have a significant contribution to hot AIA channels in the event of coronal condensation.