Triggering of eruptive flares
- L. Moore R, G. Roumeliotis
Yohkoh soft X-ray image data prior to a filament activation and eruption on 1992 May 7 reveal the presence of a bright, filamentary soft X-ray structure apparently lying low under an arcade of soft X-ray loops from which the eruption later originated. This filamentary soft X-ray feature was coexistent and partially co-spatial along the line-of-sight direction with a dark He I 1083 nm filamentary structure (which was similar in appearance to an Hα dark filament observed earlier). Prior to the start of the flare the apparently low-lying filamentary soft X-ray structure disappeared, but a bright linear feature was then seen just below several clearly visible overlying loops, consistent with the filamentary soft X-ray feature having risen in altitude. At the same time the Hα dark filament became elevated and overlapped well, along the line-of-sight direction, with the elevated linear soft X-ray feature. Some of the overlying loops brightened in soft X-rays at the time the Hα data show the Hα filament in an elevated position and rising, (but before the Hα dark filament disappearance). The overlying soft X-ray loops also showed an increase in temperature and emission at the time of the filament activation. Eventually the elevated, filamentary soft X-ray feature disappeared and several apparently cusped shaped loops were then observed in the vicinity. Within several minutes of this time the soft X-ray flare occurred. The series of Yohkoh soft X-ray images for this event together with supporting data from ground-based observatories strongly suggest that many features of the magnetic field changes associated with the eruption of the filament were seen in soft X-rays. Moreover the observations indicate that the filament and overlying arcade should be considered to be semi-independent structures that can interact with each other, rather than as parts of a large single structure, as is often assumed. We also find two types of cusped loops in this event. The first type consists of several Send offprint requests to: J.I. Khan ? Mailing address: Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, Kanagawa 229-0022, Japan (firstname.lastname@example.org) ?? Now at: Helio Research, 5212 Maryland Ave., La Cresenta, CA 91214, USA distinct narrow cusped loops prior to the flare, while the second type consists of diffuse cusped loop structures which appear to lie above the brightest parts of the bright arcade during gradual phase of the flare. Evidence is also presented which indicates that a nearby parasitic polarity emerging flux region may have played a role in destabilizing the arcade region, causing the filament activation, eruption and flare. The changes in the magnetic field extend beyond the flaring arcade to include the creation of a transient coronal hole and a dark coronal channel near the arcade.