Solar meridional circulation from twenty-one years of SOHO/MDI and SDO/HMI observations - Helioseismic travel times and forward modeling in the ray approximationZhi-Chao Liang, Laurent Gizon, Aaron C. Birch, Thomas L. Duvall and S. P. RajaguruA&A, 619 (2018) A99DOI: https://doi.org/10.1051/0004-6361/201833673
