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