1. Footpoint behavior Hugh Hudson UCB Galileo science meeting Nobeyama, July 12, 2002

2. What can footpoints teach us? How do we understand the symbiosis of energy release and particle acceleration? What is the nature of the geometrical evolution of the corona in the impulsive phase of a flare (or the acceleration phase of CME)? Recall work of Sakao (Yoyogi conference); Saita (unfinished thesis); Asai (ongoing)

3. Coronal structure and conjugacy Fletcher et al., 2001Cargill & Priest, 1995? http://isass1.solar.isas.ac.jp/~hudson/cartoons

4. B. Somov, 2002 Somov cartoon

5. Coronal separatrix structure The separatrix surfaces deform during an energy-release event The flare ribbons in the chromosphere should map into these separatrices Ribbon brightening not only reveals the energy, but also describes the coronal restructuring

6. The coronal magnetic field, assuming low beta, plays two roles simultaneously: 1)The field defines the source of energy via B 2 /8  2)The field defines the geometry of the energy release Comment

7. Warren & Warshall ApJ 560, L87, 2001 Asai et al., Y10 proceedings, 2002 Examples of conjugate behavior

8. Footpoint behavior for Aug. 25, 2001 (Metcalf et al. AGU poster )

9. Metcalf made a potential- field extrapolation and found that the separatrix structure correlated in interesting ways with the in-plane motions, but not with the out-of-plane (perpendicular to B) motions. Footpoints and separatrices

10. Particle acceleration and energy release Neupert effect (Neupert, 1968; Hudson, 1972) Soft-hard-soft spectral pattern (Parks & Winckler, 1971; Benz, 1975)

11. RHESSI 20-25 keV (purple) GOES 1-8 A (green) Neupert effect Examples of the Neupert effect

12. Lessons from the Neupert effect The energy release that fills coronal loops with hot plasma has a direct relationship with particle acceleration To a first approximation, this relationship is independent of the scale or intensity of the energy release

13. Soft-hard-soft pattern

14. F. Farnik, 2001 Another SHS example

15. A RH ESS I M- clas s flare

16. Broad-band spectral variation

17. Spectral soft-hard-soft effect

18. Lessons from soft-hard-soft Non-thermal time scales are usually not determined by trapping The spectral evolution at high energies is an intrinsic property of the acceleration mechanism Understanding hard X-ray spectral morphology will be a major RHESSI goal

19. HX/EUV overlay for Bastille flare ribbons Fletcher & Hudson, 2001

20. Ribbon evolution and photospheric B Fletcher & Hudson, 2001

21. Magnetic flux swept out in ribbon motions Fletcher & Hudson, 2001

22. Swept-out fluxes Fletcher & Hudson, 2001

23. Lessons from ribbons Ribbon shapes don’t reflect photospheric field Ribbon motions and swept-out field don’t match preconceptions In the Bastille 2000 flare, the hard X-ray footpoint brightnesses don’t match the expectation from mirroring

24. Conclusions The footpoint sources (hard X-ray or other) can teach us a lot about coronal restructuring (flares and CMEs) The lessons learned thus far don’t agree particularly well with expectations from simple models

25. Final remark The Neupert effect and the soft-hard-soft spectral pattern are dominant, but not universal The exceptions are probably well worth studying