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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

• l=0, 1, 2 modes from GONG and BiSON

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Low-degree Mode Amplitude

• l=0, 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: It’s more complicated than that.

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Structure Inversion Results

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Sound speed

Density

Fractional differencesbetween Sun and a model, in sense (Sun minus model)

from BiSON + LOWL data

(Basu et al. 1997, MNRAS 291, 243)

Results of OLA inversion of solar data

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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 zoneFrom 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).

Seismically determinedlocation of base of convection zone isrcz/R = 0.713 +/- 0.004

inversion

model

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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

WCan also (try to) usethe HeII bump in Wat r=0.98Reither by fittingor from its signatureas a sharp feature

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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

Contours at approx. 25o to axis

Surface Shear

Tachocline

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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 Patterns (Time-Radius)

MDI OLA

MDI RLS

GONG RLS

0 15 30 45 60

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Sinusoid Fits

• r=rA(r,)sin[t+r]

• 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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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)