Solar evidence for magnetic reconnection

H. S. Hudson

Space Sciences Lab, UC Berkeley

The Sun is remote

• Virtually all knowledge of solar conditions comes from remote sensing in the form of images and spectra

• There is no observational access to the fundamental scales of the plasma

• There are only limited signatures of non-thermal effects detectable by telescopes

• There is some indirect information available from the solar wind and from particles

Harry Petschek Symposium, March 22, 2006

G. A. Gary, Solar Phys. 203, 71 (2001)

(vA ~ 200 -1/2 km/s)

CH

Distribution of coronal plasma

Harry Petschek Symposium, March 22, 2006

The Semantics Problem

• Apparently, “reconnection” means changes of magnetic flux connectivity between distinct domains

• To a laboratory or space-plasma physicist, “reconnection” implies the microphysics

• To an astronomer, “reconnection” tends to be synonymous with “energy release”

• Are we talking about geometry, physics, or energy flow?

The answer is probably “YES”

Harry Petschek Symposium, March 22, 2006

Coronal reconnection sites

• “Emerging flux”

• Flares

• Coronal mass ejections

• Other coronal phenomena• Nanoflares?

Harry Petschek Symposium, March 22, 2006

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Yohkoh soft X-rays Magnetic field

Harry Petschek Symposium, March 22, 2006

TRACE movie showing flux emergence

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Harry Petschek Symposium, March 22, 2006

Possible signatures in flares/CMEs

Phenomenon Reference Comment“Disconnection” Illing-Hundhausen Flux ropes instead?

SADs McKenzie-Hudson Flows too slow?

Helix formation One TRACE movie Fits cartoon well

Flare cusp shape SXT images In gradual phase

X-ray jets Shibata Promising

Ribbon edges H observers Fits cartoon well

Termination shock Masuda et al. 1994 No radio observation

Current sheets UVCS and RHESSI Promising?

Footpoint motions HUV, HXR Promising

Anzer-Pneuman 1982

Harry Petschek Symposium, March 22, 2006

Reconnection in flares/CMEs?

CuspQuickTime™ and a

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Jet

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QuickTime™ and aPhoto decompressor

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Harry Petschek Symposium, March 22, 2006

Giovanelli (1948)

Gold & Hoyle (1961)

Longcope & Noonan (2000)Anzer & Pneuman (1982)

Cartoons stand in for theory

http://solarmuri.ssl.berkeley.edu/~hhudson/cartoons/

Harry Petschek Symposium, March 22, 2006

Problem of time scales

• Present theory (numerical models) cannot deal with the range of scales involved in a flare

• Can we then trust the microphysics to dictate the behavior of the largest scales? How do we know when reconnection will happen?

Harry Petschek Symposium, March 22, 2006

A breakthrough: separator reconnection between active regions (Longcope et al. 2005 case study) - an end-to-end study

Harry Petschek Symposium, March 22, 2006

Tsuneta, ApJ 456, L63, 1996: Petschek reconnection at an X point?

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Longcope et al., ApJ 630, 569 (2005): Not a Petschek X-point, but 3D separator

reconnection instead

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A breakthrough: reliable observations of before/after fields (Sudol & Harvey 2005 case study) show permanent changes

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GONG

SOHO/MDI

B dB

Flare of 2003 Oct. 29

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Flare of 2001 Aug. 25GONG + TRACE 1600A

Other examples withGOES times

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Interpretation of field changes

• The line-of-sight photospheric B field changes impulsively and irreversibly during every flare

• The patterns of change can guide us to a more complete understanding of the coronal restructuring: Will we at last have the means to observe flux transfer in flares directly?

• This can done much better with vector magnetograms at rapid temporal cadence (<< 1 min) - Solar-B? SDO? ATST? FASR?

Harry Petschek Symposium, March 22, 2006

Conclusions

• Magnetic reconnection certainly occurs on the quiet Sun (by the geometrical definition)

• It is not clear yet whether reconnection plays a causal role in flares or CMEs, but the circumstantial evidence is strong in the gradual phase

• Separator reconnection describes the energetics in the end-to-end study of Longcope et al.

Harry Petschek Symposium, March 22, 2006

Open questions

• Why does reconnection not happen more freely?

• What sets the time scale for flare occurrence?

• How do we understand the dominant non-thermal effects?