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Summary: THE ASTROPHYSICAL JOURNAL, 540:1126È1142, 2000 September 10
2000. The American Astronomical Society. All rights reserved. Printed in U.S.A.(
THE TOPOLOGY AND EVOLUTION OF THE BASTILLE DAY FLARE
G. AULANIER,1 E. E. DELUCA,2 S. K. ANTIOCHOS,1 R. A. MCMULLEN,2 AND L. GOLUB2
Received 2000 January 27; accepted 2000 April 14
ABSTRACT
On 1998 July 14, a class M3 Ñare occurred at 12:55 UT in AR 8270 near disk center. Kitt Peak
line-of-sight magnetograms show that the Ñare occurred in a d spot. Mees vector magnetograms show a
strong shear localized near a portion of the closed neutral line around the parasitic polarity of the d
spot. Observations of the Ñare in 171, 195, and 1600 have been obtained by TRACE, with ^40 sA
temporal and spatial resolutions. They reveal that small-scale preÑare loops above the sheared0A.5
region expanded and disappeared for more than 1 hr before Ñare maximum. During the Ñare, bright
loops anchored in bright ribbons form and grow. This occurs while large-scale dimmings, associated
with large expanding loops, develop on both sides of the active region. This suggests that the Ñare was
eruptive and was accompanied by a coronal mass ejection (CME). Magnetic Ðeld extrapolations reveal
the presence of a null point in the corona, with its associated "" spine ÏÏ Ðeld line, and its "" fan ÏÏ surface
surrounding the parasitic polarity. We show that while the whole event occurs, the intersections of the
"" fan ÏÏ and the "" spine ÏÏ with the photosphere brighten and move continuously. The interpretation of the
event shows that the magnetic evolution of the eruptive Ñare is strongly coupled with its surrounding
complex topology. We discuss evidence supporting a "" magnetic breakout ÏÏ process for triggering this
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