Other
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002mwoc.conf..139h&link_type=abstract
Multi-Wavelength Observations of Coronal Structure and Dynamics -- Yohkoh 10th Anniversary Meeting. Proceedings of the conferenc
Other
Scientific paper
The impressive S (or inverse-S) mark appearing on the lower corona, called sigmoid, is known as the manifestation of highly sheared magnetic structures (Rust and Kumar 1996). Recent studies using Yohkoh Soft X-ray Telescope (SXT; Tsuneta et al. 1991) has indicated that soft X-ray sigmoids, i.e., hot (>= 2MK) S-shaped features, are strongly linked with eruptive phenomena, such as filament eruptions, flares, and coronal mass ejections (CMEs) (Sterling and Hudson 1997; Hudson et al. 1998; Canfield et al. 1999). However, previous papers have focused on the magnetic topology (e.g., helicity, shear buildup) of the sigmoid and connection with the resultant CME (e.g., missing mass deduced from dimming), and thus the physical process involved in the sigmoid formation and eruption is still not well addressed (e.g., van Driel-Gesztelyi et al. 2000). In this paper, we present observations of two sigmoidal filaments, in which development of the cool (~104 K) sigmoids was well resolved with the high-cadence H α and microwave images (<= 30 sec). One is an active region filament and the other is a quiet region filament, whose long term evolution was reported by Glover et al. (2001). Both filaments were overlying the magnetic neutral line and their activities were associated with GOES B class flares. Comparison of SXT images and H α images illustrates that each filament almost coincides with a soft X-ray long structure that is apparently consisted of two short loops. The key features commonly observed in these filaments can be summarized as follows: i) The initial activity (small brightening) started at the middle of the sigmoidal filament. ii) The activity propagated upward crossing the filament at the junction of the two soft X-ray short loops, suggesting the so-called "tether-cutting" action (Sturrock 1989; Moore and Roumelios 1992). After the flare, the active region filament extended northward and formed an inverse-S structure, which is not visible in soft X-ray, whilst in the quiet region filament, the curved southern half of the filament disappeared but the other half remained. Microwave observation provides information on the heated plasma propagating along the magnetic features. We examine thermal evolution within the sigmoidal filaments and compare the results with the tether-cutting scenario which was proposed for flare/filament eruptions. Possible magnetic reconnection that took place below the filament is discussed.
Akioka Maki
Glover Alexi
Hori Kentaro
Ueno Satoru
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