3D Reconnection Simulations of Descending Coronal Voids

Mark Linton

in collaboration withDana Longcope (MSU)

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.

• 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

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!

• 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

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

3D Reconnected Loop DynamicsTRACE Slow mode shocks propagate along fieldlines

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

Outflow velocity: Height-Time plot

Track center ofmass of negativeBz in teardropalong dashedline.

Reconnected flow ~.4 of reconnection Alfvén speed vA┴

Distan

ce

Time

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┴

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

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.

Future Work: Multiple Reconnection Sites

• Reconnection site (red) splits into three pieces: expect same complexity CME reconnection.

Linton &

Priest 2003

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

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.