Trace observation of a flare triggered by the interaction of class I loops

TRACE, owing to its high angular and temporal resolution, has given a new view of the dynamics and structure of the transition region and corona (Golub et al., 1999; Schrijver et al., 1999). The possibility to compare high resolved transition region and coronal images to white light images taken by the same instrument with a high temporal cadence, gives the opportunity to carry on a "tomographical" and temporal analysis of active regions during highly transient phenomena such as flares, and therefore allows us to better understand the mechanisms involved in these phenomena. We have studied a flare occurred in AR 8421 on December 29, 1998 at 09:23 UT by comparing white Light, 1600 Angstrom, and 171 Angstrom images obtained by TRACE with full resolution (0".5 pixel size), high:cadence (similar to 33 sec), and average exposures (similar to 14 sec at 171 Angstrom and similar to 0.8 sec at 1600 Angstrom). The topology of the region is extremely complex and the flare seems to have been triggered by the interaction of class I loops.