Flare activity in solar active region 8421 observed by the TRACE satellite

Due to the wide range of wavelengths examined and to the high angular and temporal resolution, TRACE allows one to carry out a spatial and temporal analysis of active regions during highly transient phenomena such as flares. This provides new input to the study of the mechanisms involved in these phenomena. We have studied 3 flares that occurred in AR 8421 between 29 and 30 December 1998 by comparing white light, 1600 Angstrom, and 171 Angstrom images obtained by TRACE with BBSO H-alpha images, Mitaka magnetograms and Yohkoh hard X-ray data. The flares, characterized by sudden intensity enhancements in EUV loops and by moss brightenings, have been interpreted in the framework of the two canonical flare models: i.e. simple loop and two ribbon flares. Our analysis has shown that flare No. 1 may be interpreted as a two-ribbon flare triggered by reconnection between a sheared arcade and a new emerging flux tube. The analysis of flare No. 2 strongly supports the model of two-ribbon flares characterized by reconnection occurring at higher and higher levels as time proceeds. Finally, the analysis of flare No. 3 has given the opportunity to relate moss brightening with a probable process of chromospheric evaporation.