Constraints on Active Region Coronal Heating

摘要: We derive constraints on the time variability of coronal heating from observations so-called active region moss by Transition Region and Coronal Explorer (TRACE). The is believed to be due million-degree emission transition regions at footpoints loops whose maximum temperatures are several million degrees. two key results TRACE discussed in this paper that one generally sees only moss, not loops, exhibits weak intensity variations, � 10% over periods hours. movies showing these presented. demonstrate, using both analytic numerical calculations, lack observable places severe possible overlying moss. In particular, hot cannot truly flarelike with a sharp cutoff, but instead must quasi-steady an excellent approximation. Furthermore, significant variations implies magnitude weakly varying. implications conclusions for models will discussed. Subject headings: Sun: corona — UV radiation On-line material: mpg animation