Global Helioseismology 2: Results

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Global Helioseismology 2 Results

• Rachel Howe, NSO

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Synopsis

• Mode parameters, mode physics, and the solar
  cycle
• Frequency changes
• Width, amplitude and asymmetry
• Internal Structure
• Internal Rotation
• The overall picture
• Temporal variations

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Frequency shifts with solar cycle
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Frequency shift sensitivity
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Even splitting coefficients follow magnetic
activity distribution
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Localized global frequency shifts
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High-degree frequency shifts

• Mode frequencies are higher in active regions
• (Hindman et al, 2000).

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High-degree Frequency Sensitivity

• High-frequency modes can have anticorrelation
  with activity level.

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Note on Frequency Shifts

• Sensitivity depends mostly on frequency.
• Shifts are strongly localized to active regions.
• The effect is heavily dominated by the magnetic
  features at the surface.
• The exact mechanism (sound-speed? temperature?
  cavity size? magnetic field?) is still under
  debate.

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Mode Parameters

• Width is inversely proportional to lifetime
• Area under peak mode power (amplitude)
• Power x lifetime Energy Supply Rate

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Low-degree Mode Width

• l0, 1, 2 modes from GONG and BiSON

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Low-degree Mode Amplitude

• l0, 1, 2 modes from GONG and BiSON

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Medium-degree mode parameters

• From Libbrecht, 1988.

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Mode Energy Varies With Activity
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High-degree Mode Amplitude

• Amplitude from ring-diagram analysis is
  suppressed in active regions.

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High degree mode amplitude

• But at higher frequencies peak amplitude
  increases with frequency.

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Sensitivity varies with frequency
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Mode Width Varies With Activity
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High-degree mode width

• Peaks are broader (shorter lifetimes) in active
  regions.

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High-degree mode width

• But at higher frequencies, linewidth decreases
  with activity.

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Sensitivity varies with frequency
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Reminder

• Oscillations excited by granulation.
• Might expect active regions to make a difference.

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Summary

• For trapped modes, power and lifetime decrease
  with activity.
• High frequency non-trapped modes behave
  differently, increasing power and lifetime in
  active regions.
• The boundary between trapped and untrapped may
  change with activity level.

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Summary of the Summary

• Rule 1 Everything varies with everything else.
• Rule 2 Its more complicated than that.

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Structure Inversion Results
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Results of OLA inversion of solar data
Sound speed
Fractional differences between Sun and a model,
in sense (Sun minus model) from BiSON LOWL
data (Basu et al. 1997, MNRAS 291, 243)
Density
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Constraining solar structure models

• Neutrino discrepancy solved
• All exotic models inconsistent with measured
  frequencies
• Standard model pretty good, but still discrepancy
  below CZ
• Near surface poorly understood

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Depth of convection zone
From an inversion for sound speed, can calculate
W, which in the convection zone takes the
approximately constant value -(G1-1) (except in
regions of partial ionization).
inversion
model
Seismically determined location of base of
convection zone is rcz/R 0.713 /- 0.004
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Helium abundance
From inversions using u and Y, Richard et
al. (1998) determined helium abundance in the
solar convection zone to be 0.248 /- 0.002
Can also (try to) use the HeII bump in W at
r0.98R either by fitting or from its
signature as a sharp feature
W
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2-d structure inversion from MDI

• Based on early (1996) MDI data

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Sound-speed Inversion Results below the surface
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2-d structure remarks

• Most solar-cycle variation comes from
  near-surface activity and goes into the surface
  term in inversions.
• Is something strange (hot) happening around 60
  degrees?

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Rotation Inversion Results

• The mean rotation profile
• Residuals
• Phase and amplitude from sinusoid fits

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Rotation Inversion Results
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Rotation Inversion Results
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Penetrating flows

• Vorontsov et al 2002, Science
• MDI, new inversion technique
• High-latitude changes go deep
• Low-latitude flows down to at least 0.92R

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Zonal Flow Pattern
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Zonal Flow Pattern
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Zonal Flow Patterns (Time-Radius)
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0
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MDI OLA
MDI RLS
GONG RLS
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Sinusoid Fits

• W(r,q)W0(r,q)A(r,q)sinwtf(r,q)
• Phase (left) and amplitude (right) for 11yr
  sinusoid fits to zonal flow variation
• Fit can be improved by including 2nd harmonic.

MDI OLA
MDI RLS
GONG RLS
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Zonal Flows the Movie

• Movie based on two-harmonic sinusoid fit to
  rotation residuals.

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Rotation the Movie

• Red is faster rotation, green/blue slower.
• Different colour tables in upper and lower
  convection zone.

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Flows and Magnetic Activity (Smoothed)
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Summary of Rotation Results

• Shear layer (tachocline) divides
  differentially-rotating convection zone from
  solidly-rotating radiative interior.
• Near-surface shear has fastest rotation around
  0.95R.
• Differential pattern persists through convection
  zone, not quite radially.
• Zonal flow pattern, or torsional oscillation
  penetrates much of convection zone.
• Pattern has (weak) equatorward and (strong)
  poleward branches.
• Pattern in the interior is phase-shifted, leading
  the surface pattern.

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Credits

• Thanks to
• W. J. Chaplin (Birmingham)
• J. Christensen-Dalsgaard (Aarhus)
• B. Hindman (CU Boulder)
• J. W. Leibacher (NSO Tucson)
• M. J. Thompson (Sheffield)

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Further Reading
(Coming June 27)