2. Solar evidence for magnetic reconnection H. S. Hudson Space Sciences Lab, UC Berkeley

3. 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

4. Harry Petschek Symposium, March 22, 2006 G. A. Gary, Solar Phys. 203, 71 (2001) (v A ~ 200  -1/2 km/s) CH Distribution of coronal plasma 

5. 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”

6. Harry Petschek Symposium, March 22, 2006 Coronal reconnection sites “Emerging flux” Flares Coronal mass ejections Other coronal phenomena Nanoflares ?

7. Harry Petschek Symposium, March 22, 2006 Yohkoh soft X-rays Magnetic field

8. Harry Petschek Symposium, March 22, 2006 TRACE movie showing flux emergence

9. Harry Petschek Symposium, March 22, 2006 Possible signatures in flares/CMEs PhenomenonReferenceComment “Disconnection”Illing-HundhausenFlux ropes instead? SADsMcKenzie-HudsonFlows too slow? Helix formationOne TRACE movieFits cartoon well Flare cusp shapeSXT imagesIn gradual phase X-ray jetsShibataPromising Ribbon edges H  observers Fits cartoon well Termination shockMasuda et al. 1994No radio observation Current sheetsUVCS and RHESSIPromising? Footpoint motions H  UV, HXR Promising Anzer-Pneuman 1982

10. Harry Petschek Symposium, March 22, 2006 Reconnection in flares/CMEs? Cusp Jet SAD Helix Current sheet (?)

11. 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/

12. 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?

13. Harry Petschek Symposium, March 22, 2006 A breakthrough: separator reconnection between active regions (Longcope et al. 2005 case study) - an end-to-end study

14. Harry Petschek Symposium, March 22, 2006 Tsuneta, ApJ 456, L63, 1996: Petschek reconnection at an X point?

15. Harry Petschek Symposium, March 22, 2006 Longcope et al., ApJ 630, 569 (2005): Not a Petschek X-point, but 3D separator reconnection instead

16. Harry Petschek Symposium, March 22, 2006 A breakthrough: reliable observations of before/after fields (Sudol & Harvey 2005 case study) show permanent changes

17. Harry Petschek Symposium, March 22, 2006 GONG SOHO/MDI B dB Flare of 2003 Oct. 29

18. Harry Petschek Symposium, March 22, 2006 Flare of 2001 Aug. 25 GONG + TRACE 1600A Other examples with GOES times

19. Harry Petschek Symposium, March 22, 2006 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?

20. 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.

21. 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?