The formation and disintegration of 
-configurations is an
important problem in the study of the photospheric magnetic field. Using
eighteen years of observations at Big Bear Solar Observatory, Zirin & Liggett
(1987) summarized that -spots generally develop in three patterns:
emergence of a single complex spot cluster, or island delta; emergence of large
satellite spots very close to a large existing spot; and collision of two
distinct bipolar groups. So far, it is not clear what the origin of
-spots is, and how they emerge. Although it is proposed that a
-configuration will be naturally formed if the initial twist of a
magnetic tube is large enough when it emerges from below (Fan et al.
1999), there is not sufficient information about the physical cause of the
separation, especially, that occurring in association with large flares.
Before recent experiments, such as SOHO and TRACE, began to operate, the
observational study of the -spots was based on their short-term
morphological evolution (Tang 1983; Zirin & Liggett 1987; Zirin 1988; Wang
1992; Shi & Wang 1993), so that some important development stages may have
been lost due to the day-night cycle of the ground-based observations.
Moreover, since intensive flare activity seems to be strongly connected to
the -configuration and dynamical processes (Zirin & Tanaka 1973;
Hagyard et al. 1984; Zirin & Liggett 1987; Tanaka 1991; Schmieder
et al. 1994; Li et al. 1999; Sammis et al. 2000; Liu &
Zhang 2001), a detailed analysis with observations of TRACE is desirable.
In this paper, we present a rarely observed result with TRACE (5000 Å). A
-configuration in the active region NOAA 9077 was found to form from a
pre-existing one. We studied its separation and the current helicity
evolution. During separation, a major flare (3B/X5.7) erupted in the active
region with its ribbons at the site of the -configuration. The period
chosen for helicity measurement is over three days (13-15 July) when the
active region was at the central meridian of the solar disk.
Copyright ESO 2002