Variations of Solar Acoustic Radius from GONG low-L data
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Variations of Solar Acoustic Radius from GONG low-L data
Shukur Kholikov
NSO/GONG
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Outline
• Auto-correlation analysis
• Data: GONG, BISON, VIRGO/SPM
• Large separation or acoustic radius measurements
• Results
• Meridional flows from SH zonal modes
• Conclusions and future work
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ACF
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Large separations from GONG frequencies
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Large separations from BISON frequencies
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Large separations from ACF L= 0, 2
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Travel times:
GONG
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Correlation with the activity
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Relative changes of acoustic radius: MDI, GONG
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Relative changes of acoustic radius: BISON
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Relative changes of acoustic radius: VIRGO/SPM
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Conclusions
• Precise measurements of large separation
• Possibly we may estimate change of upper reflection
boundary during the activity cycle
• Applicable to astroseismology, stellar activity
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Meridional travel time differences using GONG
(m=0) SH time series
L=0-200
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Average CCF
T=1 gong month
∆=17º
=3 mHz
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Comparison travel time differences
Directly from velocity images
From M=0 SH coefficients
From reconstructed images using all-L SH coefficients
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Average travel time differences