Coronal shock waves observed in images

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Coronal shock waves observed in images

• H.S. Hudson
• SSL/UCB

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Outline

•   How coronal imaging should help with
  understanding shock waves
•   Origins of large-scale coronal waves
• Mach numbers

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Conclusions

• Large-scale coronal waves originate in compact
  magnetic structures
• The Mach numbers in the corona are low
• We cant yet image the CME flow field in the
  corona (ie, below coronagraph occulting edges)

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What coronal shocks should look like
Korreck et al., 2004
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Chandra E0102-72
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Imaging of coronal shocks good news and bad news

• A shock wave should provide a sharp density
  gradient, easy to detect in images
• We can observe motions in two dimensions
• The medium is optically thin gt confusion
• The wave may not be bright compared with other
  flare components
• The corona generally has low plasma beta, so the
  observed mass may not be structurally important

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• Only imaging can properly characterize the
  large-scale structure
• The solar corona isnt really accessible any
  other way

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Imaging of coronal shocks

• Type II bursts (plasma radiation)
• Moreton waves (Ha in the chromosphere)
• New modalities EIT, X-rays1, microwaves, meter
  waves, He 10830
• 1Three events Khan Aurass (2002) Narukage et
  al. (2002) Hudson et al. (2003)

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Type II burst
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Moreton-Ramsey wave and EIT wave
Thompson et al., 1998
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CH
Mann et al., AA 400, 329 (2003)
G. A. Gary, Solar Phys. 203, 71 (2001)
(vA 200 b-1/2 km/s ?)
Gopalswamy et al., JGR 106, 25251 (2001)
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Direct X-ray observation
Yohkoh 1998
Uchida 1968
EIT
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Why X-ray waves are hard to observe directly
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Field and energy are concentrated in active
regions

• Active-region magnetic fields via
  Roumeliotis-Wheatland technique (McTiernan)
• Mass loading via empirical law (Lundquist/Fisher)
  

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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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Heliospheric shocks in images?

• Maia et al., ApJ 528, L49 (2000)
• Vourlidas et al., ApJ 598, 1392 (2003)
• SOHO/UVCS

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Vourlidas et al., ApJ 598, 1392 (2003)
Where is the bow shock?
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Inferring the Mach number
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Mach number estimate for 6 May 1998 event
X-ray signal S ne2f(T) f(T)
T2 d(ln(S))/d(ln(n)) 2g
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Coronal Dimming
Movie of dimming (Aug 28, 1992)
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Dimming observed spectroscopically
Harra Sterling, ApJ 561, L216, 2001
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UVCS shock observations

• Raouafi et al., AA 434, 1039, 2004
• Mancuso et al., AA 383, 267, 2002
• Raymond et al., GRL 27, 1439, 2000

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Cartoon illustrating wave origins
cf. http//solarmuri.ssl.berkeley.edu/hhudson/car
toons
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The CME-driven shock in the corona

• The CME involves outward plasma motions
  perpendicular to the field
• We see the result of these motions as dimmings,
  but the data are not good enough to follow the
  flows nor to see a bow wave
• There is an Alfven-speed hole in the middle
  corona in which Mach numbers could be larger

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SUMMARY

• Coronal shock waves (metric type II) are blast
  waves (Uchida) launched by compact structures at
  flare onset. These propagate in an undisturbed
  corona
• The CME eruption restructures the corona and
  pushes a bow wave ahead of it into the solar
  wind. This creates a type II burst at long
  wavelengths

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Conclusions

• Large-scale coronal waves originate in compact
  magnetic structures
• The Mach numbers in the corona are low
• We cant yet image the CME flow field in the
  corona (ie, below coronagraph occulting edges)

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END
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Flare and CME energy partition