A COMPARATIVE STUDY OF CONFINED AND ERUPTIVE FLARES IN NOAA AR 10720
- Department of Astronomy, Nanjing University, Nanjing 210093 (China)
- School of Physics, Astronomy, and Computational Sciences, George Mason University, 4400 University Drive, MSN 6A2, Fairfax, VA 22030 (United States)
We investigate the distinct properties of two types of flares: eruptive flares associated with coronal mass ejections (CMEs) and confined flares without CMEs. Our study sample includes nine M- and X-class flares, all from the same active region (AR), six of which are confined and three others which are eruptive. The confined flares tend to be more impulsive in the soft X-ray time profiles and show slenderer shapes in the Extreme-ultraviolet Imaging Telescope 195 A images, while the eruptive ones are long-duration events and show much more extended brightening regions. The location of the confined flares is closer to the center of the AR, while the eruptive flares are at the outskirts. This difference is quantified by the displacement parameter, which is the distance between the AR center and the flare location; the average displacement of the six confined flares is 16 Mm, while that of the eruptive ones is as large as 39 Mm. Further, through nonlinear force-free field extrapolation, we find that the decay index of the transverse magnetic field in the low corona ({approx}10 Mm) is larger for eruptive flares than for confined ones. In addition, the strength of the transverse magnetic field over the eruptive flare sites is weaker than it is over the confined ones. These results demonstrate that the strength and the decay index of the background magnetic field may determine whether or not a flare is eruptive or confined. The implication of these results on CME models is discussed in the context of torus instability of the flux rope.
- OSTI ID:
- 21576878
- Journal Information:
- Astrophysical Journal, Vol. 732, Issue 2; Other Information: DOI: 10.1088/0004-637X/732/2/87; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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