Observations of Sunquakes from GONG and MDI

1. Observations of Sunquakes from GONG and MDI 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 Kosovichev and Zharkova, 1998

4. Original unfiltered movie

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

6. Time-distance analysis of sunquakes The expanding waves accelerates with distance because acoustic waves propagate through deeper layers for larger distances.

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. Anisotropy of July 9, 1996 sunquake

9. 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

10. Energy release and X-ray sources

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

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

13. Numerical model of the seismic response (1995)

14. After the 1996 event the seismic emission was first noticed in an integrated acoustic signal – “egression power” A.-C. Donea & C. Lindsey (2005, ApJ), “egression power”, X17 flare, Oct.28, 2003

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

16. Seismic radiation from solar flares123 Diana Besliu(1,2), Alina C. Donea(1), Paul Cally(1) http://www.maths.monash.edu.au/~adonea/DATABASE_SUNQUAKES/DIANA/site_statie/sunquakes.html

17. 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.

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

19. Sunquakes of October 28, 2003, X17 flare

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

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

22. Sunquake of July 16, 2004, X3.6 flare (MDI)

23. Sunquake of July 16, 2004, X3.6 flare (GONG)

24. Sunquake of January 15, 2005, X1.2 flare (MDI)

25. Sunquake of January 15, 2005, X1.2 flare (GONG)

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

28. 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

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

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

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

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

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

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

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

36. 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.

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

38. Location of the initial impulse

39. Northward- directed wave

40. Sourthward- directed wave

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

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

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

44. Thick-target model explains the sunquakes Chromospheric evaporation High-pressure region Photospheric shock Ref. Brown, 1971; Kostiuk & Pikelner, 1974

45. Initial impulses and seismograms January 15, 2005

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

47. 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 and decay. 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.