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tokens: We are grateful to Todd Hoeksema and Thierry Appourchaux for constructive discussion and Eric Fossat for providing the 80 s data he used. We also thank the SOHO GOLF and VIRGO/LOI teams for making their data available as per the SOHO data access policy, and the Birmingham Solar Oscillations Network group for access to the BiSON data. This work utilizes data obtained by the Global Oscillation Network Group (GONG) program, managed by the National Solar Observatory, which is operated by AURA Inc. under a cooperative agreement with the National Science Foundation. The data were acquired by instruments operated by the Big Bear Solar Observatory, High Altitude Observatory, Learmonth Solar Observatory, Udaipur Solar Observatory, Instituto de Astrofísica de Canarias, and Cerro Tololo Inter-American Observatory. We acknowledge support by HMI NASA contract NAS5-02139.