active-region magnetic structures and their perturbations by flares
DESCRIPTION
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, - PowerPoint PPT PresentationTRANSCRIPT
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MRT workshop, August 10, 2004
Active-region magnetic structures and their
perturbations by flares
H.S. Hudson
SSL/UCB
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MRT workshop, August 10, 2004
Outline
• Description of a solar active region
• Magnetic structure
• Waves, oscillations, and restructuring
• RHESSI observations of eruptive flares
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MRT workshop, August 10, 2004
TRACE 171A view of an active region,courtesy LMSAL “cool stars” Web material
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MRT workshop, August 10, 2004
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 ), 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
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MRT workshop, August 10, 2004
G. A. Gary, Solar Phys. 203, 71 (2001)
CH
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MRT workshop, August 10, 2004
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
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MRT workshop, August 10, 2004
Lundquist et al., SPD 2004
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MRT workshop, August 10, 2004
NOAA 10486, Haleakala IVM data, cube
Roumeliotis-Wheatland-McTiernan methodpixel size ~3000 km
Scaled Not scaled
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MRT workshop, August 10, 2004
AR8210 courtesy J. McTiernan
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MRT workshop, August 10, 2004
Conjecture: Most of the free energy in an active region is concentrated very near its base
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MRT workshop, August 10, 2004
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
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MRT workshop, August 10, 2004
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
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MRT workshop, August 10, 2004Aschwanden et al., Solar Phys. 206, 99 (2002)
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MRT workshop, August 10, 2004
Narukage et al., PASJ 56, L5 (2004)
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MRT workshop, August 10, 2004
SUMER’s oscillations
Wang, T. J. et al., ApJ 574, L101 (2003)
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MRT workshop, August 10, 2004
Yohkoh’s oscillations (BCS)
Mariska, J. et al., SPD poster (2004)
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MRT workshop, August 10, 2004
QuickTime™ and aPhoto decompressor
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Schrijver et al., Solar Phys. 206, 69, 2002
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MRT workshop, August 10, 2004
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)
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MRT workshop, August 10, 2004
SXT observations of the blow-out of anX-ray “loop prominence system”
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MRT workshop, August 10, 2004
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
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MRT workshop, August 10, 2004
H. Wang et al., ApJ 576, 497 (2002)
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MRT workshop, August 10, 2004
Magnetic challenge: Can any existingmodel of a flare or CME properly describethe change in the coronal magnetic field?
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MRT workshop, August 10, 2004
Cartoon showing magnetic implosion
Post-event fieldPre-event field
Isomagnetobars
Limb
Hudson & Cliver, JGR 106, 25,199 (2001)
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MRT workshop, August 10, 2004
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/
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MRT workshop, August 10, 2004
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)
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MRT workshop, August 10, 2004
From the Flare/CME Cartoon Archivehttp://solarmuri.ssl.berkeley.edu/~hhudson/cartoons/
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MRT workshop, August 10, 2004
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Null?
Separatrices?
Anzer-Pneuman, 1982
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MRT workshop, August 10, 2004
Forbes, T., JGR 105, 23,153, 2000Gallagher, P. personal communication 2004
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MRT workshop, August 10, 2004
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MRT workshop, August 10, 2004
RHESSI observations of early inward motions
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MRT workshop, August 10, 2004Sui et al., 2004
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MRT workshop, August 10, 2004
Sui et al., 2004