Time-distance diagrams using a (Dirichlet) and (Atmo SAI 1) BCs by selecting the frequencies around 3 mHz (left) and 6.5 mHz (right). The cross-covariance is filtered using a phase speed filter centered at 125.2 km s^-1 for 3 mHz and 250.4 km s^-1 for 6.5 mHz and a width of 12.3 km s^-1. The dashed black lines indicate the location of the cuts shown at the bottom in order to emphasize the amplitude ratios between the first and second skip.