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H. Wang, J. Qiu, J. Chae, C. Lee, P. Goode (Big Bear Solar Obs., NJIT)
On September 27, 1998, Big Bear Solar Observatory (BBSO) and Transition Region and Coronal Explorer (TRACE) coordinated observations from 16:00 to 19:00 UT to study properties of microflares on AR NOAA #8340. Fortuitously, a C5.2 flare occurred at 16:30UT in this active region. H\alpha and magnetograph movies were obtained at BBSO; CIV 1550Å, FeIX 171Å, and FeXII 195Åmovies were obtained by TRACE; both with a cadence about 1 minute. In this paper, we concentrate on the study of magnetic properties of 70 CIV microflares, as well as their relationship to the C5.2 flare. We obtained the following results: (1) We found two kinds of microflares: (a) microflares of transient brightenings with a time scale of 1 to 5 minutes (impulsive events). 90% of the microflares are of this form. Most of the events in this category are associated with well defined magnetic neutral lines, although a few of them are not located near a neutral line; and (b) microflares lasting half an hour or longer (persistent events). Seven events in three clusters belong to this category. All three sites are associated with a dominant magnetic polarity plus a very small element of opposite polarity. (2) More than a third of the impulsive microflares occurred near the C5.2 flare site indicating that a local instability is responsible for both the C5.2 flare and microflares. This indirectly support the avalanche theory of flare energy release, which predicts that a big flare may be associated with many small flares. Based on the morphologies of those events, we postulate that the persistent events may be due to loop interaction; while impulsive events may be associated with sheared loop structure.
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