Seismology of the Solar Atmosphere

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Seismology of the Solar Atmosphere

• HELAS Roadmap Workshop, OCA Nice
• Wolfgang Finsterle, PMOD/WRC, Davos, Switzerland

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Seismology of the Solar Atmosphere

• Conceptual ideas
• Traveling waves
• Wave travel times
• Many different types of waves (MAG, Alfvén, etc.)
• Techniques
• Multi-height observations
• Doppler-grams
• Cross-correlation analysis
• Scientific potential
• Dispersion relation of the solar atmosphere
• Diagnostics of magnetic fields
• Chromospheric heating

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The Atmospheric Wave Field

• Solar eigenmodes oscillate in phase at all
  heights in the solar atmosphere
• Traveling waves produce a relative phase shift
  which is characteristic to the observation height
  and depends on the sound speed structure

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Acoustic Probing of the Sun's Lower Atmosphere

• By cross-correlating the wave fields at different
  heights, we can estimate the wave paths and sound
  speed between the observed heights
• The results naturally link to the solar interior,
  where seismic models are well established
• Sound waves interact with magnetic fields
  (absorption, wave conversion/transmission)

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Phase Travel Time K?Na
Phase time (tp)
Qualitatively the same structures as in the group
travel time, but numerically much more stable,
hence less noisy.
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Phase Travel Time
MDI magnetogram
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1. Acoustic Portals
Jefferies et al. 2006, ApJ 648, L151

• Inclined magnetic field lines at the boundaries
  of supergranules locally lower the acoustic
  cut-off frequency
• Acoustic portals for low-frequency waves (lt5 mHz)
  to propagate into the solar atmosphere
• Chromospheric heating

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3. What are we looking at?Some Thoughts about
Doppler-Grams

• Line-of-sight velocities of the observed medium
  introduce Doppler shifts
• Dopplergrams filter for anti-parallel intensity
  changes in the red and blue wings of absorption
  lines
• The red- and blue-wing probes observe different
  heights in the solar atmosphere
• At high frequencies, the acoustic wavelengths
  become comparable to this separation
• ? Frequency-dependent Doppler-grams