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Global Helioseismology 2: Results

Global Helioseismology 2: Results. Rachel Howe, NSO. Synopsis. Mode parameters, mode physics, and the solar cycle Frequency changes Width, amplitude and asymmetry Internal Structure Internal Rotation The overall picture Temporal variations. Frequency shifts with solar cycle.

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Global Helioseismology 2: Results

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  1. Global Helioseismology 2: Results Rachel Howe, NSO

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

  3. Frequency shifts with solar cycle

  4. Frequency shift sensitivity

  5. Even splitting coefficients follow magnetic activity distribution

  6. Localized global frequency shifts

  7. High-degree frequency shifts • Mode frequencies are higher in active regions • (Hindman et al, 2000).

  8. High-degree Frequency Sensitivity • High-frequency modes can have anticorrelation with activity level.

  9. 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.

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

  11. Low-degree Mode Width • l=0, 1, 2 modes from GONG and BiSON

  12. Low-degree Mode Amplitude • l=0, 1, 2 modes from GONG and BiSON

  13. Medium-degree mode parameters • From Libbrecht, 1988.

  14. Mode Energy Varies With Activity

  15. High-degree Mode Amplitude • Amplitude from ring-diagram analysis is suppressed in active regions.

  16. High degree mode amplitude • But at higher frequencies peak amplitude increases with frequency.

  17. Sensitivity varies with frequency

  18. Mode Width Varies With Activity

  19. High-degree mode width • Peaks are broader (shorter lifetimes) in active regions.

  20. High-degree mode width • But at higher frequencies, linewidth decreases with activity.

  21. Sensitivity varies with frequency

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

  23. 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.

  24. Summary of the Summary • Rule 1: Everything varies with everything else. • Rule 2: It’s more complicated than that.

  25. Structure Inversion Results

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

  27. 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

  28. Depth of convection zone From an inversion for sound speed, can calculate W, which in the convection zone takes the approximately constant value -(Γ1-1) (except in regions of partial ionization). inversion model Seismically determined location of base of convection zone is rcz/R = 0.713 +/- 0.004

  29. 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 r=0.98R either by fitting or from its signature as a sharp feature W

  30. 2-d structure inversion from MDI • Based on early (1996) MDI data

  31. Sound-speed Inversion Results – below the surface

  32. 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?

  33. Rotation Inversion Results • The mean rotation profile • Residuals • Phase and amplitude from sinusoid fits

  34. SurfaceShear Contours at approx. 25o to axis Tachocline Rotation Inversion Results

  35. Rotation Inversion Results

  36. 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

  37. Zonal Flow Pattern

  38. Zonal Flow Patterns (Time-Radius) 15 30 0 45 60 MDI OLA MDI RLS GONG RLS

  39. Sinusoid Fits • W(r,q)=W0(r,q)+A(r,q)sin[wt+f(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

  40. Zonal Flows – the Movie • Movie based on two-harmonic sinusoid fit to rotation residuals.

  41. Flows and Magnetic Activity (Smoothed)

  42. 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.

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

  44. Further Reading (Coming June 27)

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