Observations of the MHD and helioseismic responses to flare energy-release events

1. Observations of the MHD and helioseismic responses to flare energy-release events Alexander Kosovichev Stanford University

2. Seismic response to solar flares: “Sunquakes” • Sunquakes are expanding ring-like waves excited by solar flares and observed on the Sun’s surface.

3. First sunquake: July 9, 1996

4. The sequence of events in sunquakes Shock wave hits the photosphere during the impulsive phase Expanding ring wave is observed 20 min later

5. Time-distance diagram of the sunquake The expanding waves accelerates with distance because acoustic waves propagate through deeper layers for larger distances.

6. Ray paths of acoustic waves from an impulsive source

7. Sunquakes correlate with hard X-ray flux These observations suggest that sunquakes are excited by shock waves propagating downward from the chromosphere into the photosphere, formed by heating of the chromosphere by high-energy electrons – “thick-target” model.

8. Why study sunquakes? • Understanding of the physics of the flare energy release and transport • Interaction between the high-energy particles and solar plasma • Dynamical processes in solar flares (formation of shocks, chromospheric evaporation) • Magnetic field topologies and reconnections associated with flares • New helioseismic diagnostics • Direct observations of interaction of acoustic waves with magnetic field of sunspots and flow fields

9. Energy release and X-ray sources

10. Energy transport: thick-target model Chromospheric evaporation High-pressure region Photospheric shock Ref. Brown, 1971; Hudson, 1972; Kostiuk & Pikelner, 1974

11. Numerical simulations of the hydrodynamic response to solar flares (thick-target model) (Livshits, Kosovichev et al 1980).

12. Numerical model of the seismic response

13. New sunquakes • October 28, 2003, X17 – three events • October 29, 2003, X10 • July 16, 2004, X3.6 • January 15, 2005, X1.2 • No sunquake of comparable magnitude was observed between 1996 and 2003.

14. Sunspot counts and X-flares during the last three solar cycles. Graphic courtesy David Hathaway, NASA/NSSTC.

15. The new sunquakes were first noticed in an integrated acoustic signal – “egression power” A.-C. Donea & C. Lindsey, “egression power”, X17 flare, Oct.28, 2003

16. A.-C. Donea & C. Lindsey, “egression power”, X10 flare, Oct.29, 2003

17. Sunquakes of October 28, 2003, X17 flare

18. Doppler images of the wave fronts of X17 flare of October 28, 2003

19. Time-distance diagram of an October 28, 2003, event

20. Sunquake of July 16, 2004, X3.6 flare

21. Sunquake of January 15, 2005, X1.2 flare

23. Extremely narrow directed wave of October 29, 2003, X10 flare Can the wave collimation be caused by strong subsurface flows?

24. X-ray, g-ray and acoustic sources of X17 flare, October 28, 2003 Doppler sources > 1 km/s Hard X-ray sources Gamma-ray sources

25. Magnetic energy release and subsurface dynamics • X10 and X17 flares of October 28-29, 2003

26. X10 (Halloween) flare, Oct. 29, 2003, 20:37 UT –MDI magnetogram movie

27. Energy release site Magnetic field change associated with X10 flare of Oct. 29, 2003 20:28 UT

28. Energyrelease site Subsurface flow map obtained by time-distance helioseismology during X10 flare

29. X17.2 flare, Oct. 28, 2003, 9:51 UT

30. Energy release site X17.2 flare, Oct. 28, 2003, 9:51 UT

31. Subsurface flow map obtained by time-distance helioseismology during X10 flare Energy release site

32. The regions of the magnetic energy release in solar flares appear to be related to strong shearing plasma motions at the depth of 4-6 Mm.

33. January 15, 2005, X1.2 flare:magnetogram (color) and Dopplergram (b/w) Wave front

34. Location of the initial impulse

35. Northward- directed wave

36. Sourthward- directed wave

37. January 15, 2005, X1.2 flare:magnetogram and hard X-ray image 0:41 UT Hard X-ray source

38. January 15, 2005, X1.2 flare:Magnetogram, soft and hard X-ray images Soft X-ray source Hard X-ray source

39. January 15, 2005, X1.2 flare:Dopplergram and hard X-ray image 0:41 UT Velocity source (shock) Hard X-ray source

40. January 15, 2005, X1.2 flare: Doppler and hard X-ray sources Two shocks generated by two beams of high-energy electrons

41. Initial impulses and seismograms January 15, 2005

42. Conclusions • Expanding seismic waves (“sunquakes”) excited by solar flares are highly anisotropic having the highest amplitude in the direction of the expansion of the flare ribbons. • The source of sunquakes are downward propagating shocks (observed in MDI Dopplergrams); it correlates with hard X-ray emission (as in the thick-target flare model). • The wave fronts propagate through areas of magnetic field and sunspots without significant distortion. The time-distance relations show relatively small variations consistent with the time-distance helioseismology measurements using the cross-covariance functions. • Sunquakes provide great data for studying the structure of active regions and flare physics • It is intriguing that strong sunquakes were observed only in the declining phases of the solar cycle. This might be related to fundamental changes in the topology of active regions resulting in changes in the energy release properties (e.g. energy release height). • Need numerical models and new observations with higher spatial and temporal resolution, and also spectral data – an excellent target for Solar-B observations.

43. Solar-B can study sunquakes for: • Understanding of the physics of the flare energy release and transport • Interaction between the high-energy particles and solar plasma • Dynamical processes in solar flares (formation of shocks, chromospheric evaporation) • Magnetic field topologies and reconnections associated with flares • Developing new helioseismic diagnostics • Direct observations of interaction of acoustic waves with magnetic field of sunspots and flow fields

44. Suggestion for Solar-B observing program • Prior a flare: • SOT/FPP – vector magnetograms and Doppler velocity (1-min cadence for local helioseismology) • Flare impulsive phase (first 20 min after the flare trigger): • SOT/FPP – spectrograms • XRT/EIS – high-cadence flare program • Hard X-ray images are important (keep RHESSI alive) • Sunquake phase (20 min after the hard X-ray impulse): • SOT/FPP - vector magnetograms and Doppler velocity (30-sec cadence)