Travel-time maps are computed from ten-day averages of cross covariances. The cross covariances are ν-filtered with filters centered at 3.1 and 4.0 mHz before the travel times are fitted with the Gabor wavelets. Similar 9-day average quiet Sun maps are averaged over the map and similarly ν-filtered to construct reference travel times which are subsequently subtracted from those of the sunspot maps. The phase (envelope) times [τp] are plottedin the upper (middle) line for the 3.1 mHz in the left column and for the 4.0 mHz in the right column. Overplotted on the upper four maps are the contours of the umbral–penumbral boundary (red) and the penumbral–photosphere boundary (blue) as shown in the earlier figure. In the lower left and lower right are shown cuts in the north–south direction averaged over the east–west direction between the pair of vertical white lines shown overplotted on the maps. Error bars are computed from the scatter of the east–west averages. Also overplotted on these cuts are theaverage umbral–penumbral boundary (heavy black lines) and the penumbral–photosphere boundary (thin dashed lines).
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