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

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