HESSI Science Meeting Berkeley Dec 2000

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Multi-wavelength Observations of a Solar
Flare -Evidence for Spine-Fan Reconnection?
Lyndsay Fletcher Department of Physics and
Astronomy, University of Glasgow
Tom Metcalf and David Alexander Lockheed Martin
Solar and Astrophysics Lab Palo Alto, CA
Daniel Brown Department of Mathematics and
Computational Sciences University of St. Andrews
HESSI Science Meeting Berkeley Dec 2000
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Talk Outline

• Introduction
• 3-May-99 Flare Data Summary
• 3-D topological modeling of the event
• Flare evolution
• Conclusions

HESSI Science Meeting Berkeley Dec 2000
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In large arcade or 2-ribbon flares,
particularly those observed on the limb, 2-D
models do a decent job of describing the later
phases of the flare, presence of double HXR
footpoints, looptop HXR sources etc.
HESSI Science Meeting Berkeley Dec 2000
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But flares are far from 2-D.
HESSI Science Meeting Berkeley Dec 2000
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- -
(from Priest Schrijver 2000)
In 2-D, reconnection occurs at magnetic X-points
in 3-D it occurs at magnetic separators.
Importantly, as regions of strong discontinuity
in B, separators should carry large currents,
which may help locate them.
HESSI Science Meeting Berkeley Dec 2000
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M 1.9 Flare of 3-May-1999
HESSI Science Meeting Berkeley Dec 2000
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TRACE flare movies
Lyman a movie
171 A movie
HESSI Science Meeting Berkeley Dec 2000
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Features of the flare seen by TRACE
Discrete bright kernels
core - single bright loop
ejecta
HESSI Science Meeting Berkeley Dec 2000
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Yohkoh/SXT observations.
HESSI Science Meeting Berkeley Dec 2000
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Alignment of TRACE, HXT, SXT
HXT source in all channels is a short-lived
(2min) single footpoint
Location is at the south end of the TRACE/SXT core
HESSI Science Meeting Berkeley Dec 2000
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The local magnetic field
A potential field extrapolation is made
using data from SoHO/MDI
HESSI Science Meeting Berkeley Dec 2000
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The presence of local and distant connections
originating from nearby locations implies a
separatrix dome surrounding the small area of
positive field.
Positive field
Distant field connections (green)
Local field connections (purple)
HESSI Science Meeting Berkeley Dec 2000
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Spine-Fan Geometry
A separatrix dome is formed by fan field
lines, and divides locally closed field from
larger-scale field of the active region -
imagine the fan field lines here bending down to
touch the photosphere
(from Craig and McClymont 97)
HESSI Science Meeting Berkeley Dec 2000
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Over a day or so, the small positive field region
is observed to move southwards into the negative
field. Small-scale EUV brightenings suggest that
flux cancellation and heating is occurring.
HESSI Science Meeting Berkeley Dec 2000
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We have reduced the complicated flare magnetic
field down a few topological elements sources,
nulls and some illustrative field lines
Note the presence of N, a coronal null point.
What happens if the sources are moved in
accordance with observations?
HESSI Science Meeting Berkeley Dec 2000
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Reconnection at the coronal null leads to open
fieldlines closing down, and closed fieldlines
opening. This dynamic process should produce
heating and ejecta, as is observed.
HESSI Science Meeting Berkeley Dec 2000
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Other authors are interpreting complex flare
events (such as the oscillating loop flare
here) in terms of their basic topology. Here, a
null and separator field lines in a spine and
fan configuration suggest the observed
distribution of bright field lines.
Aulanier et al 2000
HESSI Science Meeting Berkeley Dec 2000
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Conclusions
In the example presented here, a topological
model involving reconnection through a coronal
null is capable of a qualitative, but integrated
explanation of many flare phenomena.
Our present ability to make simultaneous
multi-wavelength observations of the sun with
high time cadence and high spatial resolution
driving theory and interpretation Future looks
good for HESSI and TRACE
HESSI Science Meeting Berkeley Dec 2000