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Sunquake Observations and Understanding Flare Energy Release

Explore the seismic responses to solar flares, known as "Sunquakes," and their implications in understanding flare energy release, particle interactions, and magnetic field topologies. Discover the dynamics of solar flares, chromospheric evaporation, and magnetic field reconnections. Dive into numerical simulations and new helioseismic diagnostics to study sunquakes events and their significance in solar physics. Analysis of sunquakes reveals anisotropic seismic waves and their correlation with downward propagating shocks and hard X-ray emissions. Utilize sunquakes data for in-depth investigations into the structure of active regions and flare physics. The study suggests that strong sunquakes occur during the declining phases of the solar cycle, offering intriguing insights into solar phenomena.

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Sunquake Observations and Understanding Flare Energy Release

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  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

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

  23. 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

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

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

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

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

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

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

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

  31. 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.

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

  33. Location of the initial impulse

  34. Northward- directed wave

  35. Sourthward- directed wave

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

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

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

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

  40. Initial impulses and seismograms January 15, 2005

  41. 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.

  42. 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

  43. 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)

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