Magnetic Neutral Lines in Flare-productive Active Regions

Author_list: T.T.Ishii, S.Saito, and H.Kurokawa


Abstract: A flare-productive active region NOAA 9026 (2000 June)
provided us with a rare opportunity to study a new important aspect of
a twisted magnetic flux rope and its rapidly-untwisting motions to have
caused strong flares.  Based on the analyses of the evolution of this
region, we found pre-flare brightenings in TRACE 1600 A images about
two hours prior to an X-class flare.  Active region NOAA 10486 is the
most flare-productive region during this solar cycle, which has
produced seven X-class flares including X28 flare on Nov. 4, 2003.  We
studied the formation process of delta-type magnetic configuration, and
found pre-flare brightenings in TRACE 1600 A images on the sheared
neutral lines.  We studied the evolution of all the active regions in
this solar cycle (cycle 23) that have produced at least one X-class
flare and have been observed by SOHO/MDI magnetograms.  We are planning
to summarize the characteristics of flare-productive regions from the
viewpoint of pre-flare brightenings and rotational motions of magnetic
neutral lines.