Active-region magnetic structures and their perturbations by flares

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Active-region magnetic structures and their
perturbations by flares

• H.S. Hudson
• SSL/UCB

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Outline

• Description of a solar active region
• Magnetic structure
• Waves, oscillations, and restructuring
• RHESSI observations of eruptive flares

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TRACE 171A view of an active region, courtesy
LMSAL cool stars Web material
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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

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CH
G. A. Gary, Solar Phys. 203, 71 (2001)
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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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Lundquist et al., SPD 2004
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NOAA 10486, Haleakala IVM data, B cube
Scaled
Not scaled
Roumeliotis-Wheatland-McTiernan method pixel size
3000 km
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AR8210 courtesy J. McTiernan
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Conjecture Most of the free energy in an
active region is concentrated very near its base
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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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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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Aschwanden et al., Solar Phys. 206, 99 (2002)
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Narukage et al., PASJ 56, L5 (2004)
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SUMERs oscillations
Wang, T. J. et al., ApJ 574, L101 (2003)
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Yohkohs oscillations (BCS)
Mariska, J. et al., SPD poster (2004)
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Schrijver et al., Solar Phys. 206, 69, 2002
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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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SXT observations of the blow-out of an X-ray
loop prominence system
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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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H. Wang et al., ApJ 576, 497 (2002)
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Magnetic challenge Can any existing model of a
flare or CME properly describe the change in the
coronal magnetic field?
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Cartoon showing magnetic implosion
Post-event field
Pre-event field
Isomagnetobars
Limb
Hudson Cliver, JGR 106, 25,199 (2001)
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Conclusions

• Unlike the cosmologists, we dont have a standard
  model for a flare/CME - we do have cartoons,
  though http//solarmuri.ssl.berkeley.edu/hhudson
  /cartoons/

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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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From the Flare/CME Cartoon Archive http//solarmur
i.ssl.berkeley.edu/hhudson/cartoons/
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Anzer-Pneuman, 1982
Null?
Separatrices?
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Forbes, T., JGR 105, 23,153, 2000
Gallagher, P. personal communication 2004
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(No Transcript)
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RHESSI observations of early inward motions
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Sui et al., 2004
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Sui et al., 2004