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
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
ACF
Large separations from GONG frequencies
Large separations from BISON frequencies
Large separations from ACF L= 0, 2
Travel times:
GONG
Correlation with the activity
Relative changes of acoustic radius: MDI, GONG
Relative changes of acoustic radius: BISON
Relative changes of acoustic radius: VIRGO/SPM
Conclusions
• Precise measurements of large separation
• Possibly we may estimate change of upper reflection
boundary during the activity cycle
• Applicable to astroseismology, stellar activity
Meridional travel time differences using GONG
(m=0) SH time series
L=0-200
Average CCF
T=1 gong month
∆=17º
=3 mHz
Comparison travel time differences
Directly from velocity images
From M=0 SH coefficients
From reconstructed images using all-L SH coefficients
Average travel time differences