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Active-region magnetic structures and their perturbations by flares

Active-region magnetic structures and their perturbations by flares. H.S. Hudson SSL/UCB. Outline. Description of a solar active region Magnetic structure Waves, oscillations, and restructuring RHESSI observations of eruptive flares. TRACE 171A view of an active region,

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Active-region magnetic structures and their perturbations by flares

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  1. Active-region magnetic structures and their perturbations by flares H.S. Hudson SSL/UCB MRT workshop, August 10, 2004

  2. Outline • Description of a solar active region • Magnetic structure • Waves, oscillations, and restructuring • RHESSI observations of eruptive flares MRT workshop, August 10, 2004

  3. TRACE 171A view of an active region, courtesy LMSAL “cool stars” Web material MRT workshop, August 10, 2004

  4. Mechanical properties of an active region in the corona • Flares and CMEs are magnetically driven, according to consensus, from energy stored in the corona • In such conditions, (low plasma b), the mechanical stresses can be represented as a pressure and a tension • Dissipation is normally slow • The volume is electrically equipotential except for the Rosseland-Pannekoek potential MRT workshop, August 10, 2004

  5. CH G. A. Gary, Solar Phys. 203, 71 (2001) MRT workshop, August 10, 2004

  6. What are the loops? • The loops show the direction of the magnetic field • The X-ray visibility of the corona is a monotonic increasing function of the gas pressure • In an active region, the loop dimensions are typically smaller than the scale height • The footpoints of a loop lie in a transition layer at the appropriate pressure • The magnetic field must be slightly depressed in the visible loops MRT workshop, August 10, 2004

  7. Lundquist et al., SPD 2004 MRT workshop, August 10, 2004

  8. NOAA 10486, Haleakala IVM data, |B| cube Scaled Not scaled Roumeliotis-Wheatland-McTiernan method pixel size ~3000 km MRT workshop, August 10, 2004

  9. AR8210 courtesy J. McTiernan MRT workshop, August 10, 2004

  10. Conjecture: Most of the free energy in an active region is concentrated very near its base MRT workshop, August 10, 2004

  11. The normal state of the active-region corona is an equilibrium • An equilibrium system will oscillate around its rest configuration if perturbed slightly • We observe coronal oscillations via spectroscopy, photometry, and in movies • The oscillations have small amplitudes and can be studied via MHD theory MRT workshop, August 10, 2004

  12. Kink-mode oscillations • Flare waves associated with metric type II bursts often (12/30 cases) appear with TRACE loop oscillations • These oscillations allow us to study the equilibrium state of the non-erupting part of the corona MRT workshop, August 10, 2004

  13. Aschwanden et al., Solar Phys. 206, 99 (2002) MRT workshop, August 10, 2004

  14. Narukage et al., PASJ 56, L5 (2004) MRT workshop, August 10, 2004

  15. SUMER’s oscillations Wang, T. J. et al., ApJ 574, L101 (2003) MRT workshop, August 10, 2004

  16. Yohkoh’s oscillations (BCS) Mariska, J. et al., SPD poster (2004) MRT workshop, August 10, 2004

  17. Schrijver et al., Solar Phys. 206, 69, 2002 MRT workshop, August 10, 2004

  18. Three things the movie showed • Early inward motions, prior to the eruption • Dimming - the CME starting off • Excitation of coupled normal modes in the arcade • (arcade blowout) MRT workshop, August 10, 2004

  19. SXT observations of the blow-out of an X-ray “loop prominence system” MRT workshop, August 10, 2004

  20. Studying coronal equilibria • On large scales the corona tends be stable • We can study the equilibrium states via the oscillations; there are several modalities • Propose to use “instrumented hammer” approach to characterize eigenstates • Propose to study before/after equilibrium states using FASR and Solar-B MRT workshop, August 10, 2004

  21. H. Wang et al., ApJ 576, 497 (2002) MRT workshop, August 10, 2004

  22. Magnetic challenge: Can any existing model of a flare or CME properly describe the change in the coronal magnetic field? MRT workshop, August 10, 2004

  23. Cartoon showing magnetic implosion Post-event field Pre-event field Isomagnetobars Limb Hudson & Cliver, JGR 106, 25,199 (2001) MRT workshop, August 10, 2004

  24. Conclusions • Unlike the cosmologists, we don’t have a standard model for a flare/CME - we do have cartoons, though: http://solarmuri.ssl.berkeley.edu/~hhudson/cartoons/ MRT workshop, August 10, 2004

  25. Serious conclusions • Extrapolation techniques to learn about the coronal magnetic field are inherently flawed • It will be better in the future to assimilate more precise methods, such as - TRACE coronal imagery (direction of B) - FASR gyroresonance surfaces (magnitude of B) - Mechanical models (matching eigenfrequencies) MRT workshop, August 10, 2004

  26. From the Flare/CME Cartoon Archive http://solarmuri.ssl.berkeley.edu/~hhudson/cartoons/ MRT workshop, August 10, 2004

  27. Anzer-Pneuman, 1982 Null? Separatrices? MRT workshop, August 10, 2004

  28. Forbes, T., JGR 105, 23,153, 2000 Gallagher, P. personal communication 2004 MRT workshop, August 10, 2004

  29. MRT workshop, August 10, 2004

  30. RHESSI observations of early inward motions MRT workshop, August 10, 2004

  31. Sui et al., 2004 MRT workshop, August 10, 2004

  32. Sui et al., 2004 MRT workshop, August 10, 2004

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