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

¹ Dipartimento di Fisica e Astronomia, Cittá Universitaria, Via S. Sofia 78, 95125 Catania, Italy
² Mathematical Science Dept., St. Andrews University, St. Andrews, KY16 9SS, UK

Corresponding author: F. Zuccarello, fzucca@alpha4.ct.astro.it

Received: 7 August 2000
Accepted: 12 September 2002

Abstract

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 , and 171  images obtained by TRACE with BBSO 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.