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3D Reconnection Simulations of Descending Coronal Voids
Mark Linton
in collaboration withDana Longcope (MSU)
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TRACE Observation:Post-CME Reconnected Flux Tubes?
3D structures:• Descending tadpole-like
features below flare site penetrate into post-reconnection, 10MK plasma.
• 3D tangle of 1.6MK flare loops form at higher and higher altitudes as reconnected flux builds up.
Does 3D patchy reconnection explain descending voids and coronal loop structures?
See, e.g.,McKenzie & Hudson 1999Gallagher et al. 2002Sheeley et al. 2004, Asai et al 2004. TRACE 195Å.
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• Obtain velocities up to 2,000 km/s
• Obtain secondary reconnection in low corona: flaring and particle acceleration
How does fully 3D reconnection form post-eruption arcade loops?
2D MHD Breakout Model for CME Initiation
MacNeice et al. 2004
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Steady State 2D Reconnection:• Fast reconnection:
diffusion, reconnection localized to small region in current sheet, e.g. by localized resistivity.
• Ejected field, plasma: flows up/down from site of reconnection at vA.
• Slow mode shocks: primary source of magnetic to kinetic energy conversion.
Petschek (1964)
2D reconnection behind CME Not steady-state!
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• Initiate reconnection in small region of current sheet
• Slow mode shocks form classical X-shape
• Shut off reconnection: Slow mode shocks form teardrop shape.
• Fast mode shock communicates reconnection to distant fieldlines
Finite Duration 2D Reconnection:
After Biernat, Heyn & Semenev, 1987. See also Nitta et al, 2001
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Burst of 3D Reconnection in Localized Sphere
• Resistive sphere (countours) on current sheet: 100 times background resistivity.
• MHD simulation of localized, short burst of reconnection.
• Slow mode shocks propagate out of 2D plane.
Linton and Longcope
2005
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3D Reconnected Loop DynamicsTRACE Slow mode shocks propagate along fieldlines
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Descending Voids (Observed) versus Reconnected Flux Tubes (Simulated)
Qualitative resemblance of teardrop shapes in observations to simulation results
Cross-sectional shape depends on duration of reconnection
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Outflow velocity: Height-Time plot
Track center ofmass of negativeBz in teardropalong dashedline.
Reconnected flow ~.4 of reconnection Alfvén speed vA┴
Distan
ce
Time
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Simulated Velocities of Reconnected Flux Tubes
• Velocity increases with angle between the fields (smaller drag force?)
Goal: Study Corona by
modifying parameters to match observed velocities.
Aim for quantitative match between flare observations and 3D simulations.
Linton & Longcope 2005
• Simulations show velocities of
~ 0.2 to 0.8 vA┴
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Velocities of Reconnected Flux TubesHeight-time plots of running difference images show descending post-CME coronal
loops in both low and high Corona.
TRACE (~ .1 R_sun)height-time plot: velocities ~200km/s,
decel’n ~ 1.5km/s2
Sheeley, Warren
and Wang, 2004
LASCO (~4 R_sun)height-time plot:velocities ~50km/sdecel’n ~ 3m/s2
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Future Work: 3D Reconnected Tube Velocities in 2D Current Sheet
Syrovatskii-Green current sheet:
vA┴ ~ √(x+1) along the purple line.
Tube trajectory should be parabolic.Goal – Probe Coronal current sheet geometry by matching simulated deceleration profile to observations.
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Future Work: Multiple Reconnection Sites
• Reconnection site (red) splits into three pieces: expect same complexity CME reconnection.
Linton &
Priest 2003
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Summary
↓
• Single burst of reconnection in simple 1D current sheet: - Pair of flux tubes formed - Slow mode shocks propagate along flux tubes - Flux tube cross-sections form teardrop shapes
- Tubes propagate at ~ vA ┴ /2
• Collision of magnetic fields to form 3D current sheet: - 3D tearing mode generates several reconnection sites - Reconnected flux tubes tangle about each other - Flux tubes must reconnect again to untangle
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Future Work
↓
Detailed comparisons of observations with 3D simulations.Probe coronal reconnection by comparing simulations with
observations of voids and coronal arcade loops.
• Simulate 3D reconnection in 2D Y-type current sheet.• Observe voids in multiple wavelengths with Solar-B EIS
spectrometer.• Compare velocity profiles, shapes of voids in
simulations vs. observations.
• Simulate multiple, patchy reconnection sites.• Observe 3D geometry of post-flare coronal loops.• Compare observed arcade geometry with simulated
geometry.