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Fig. 1


Rays for the two-skip method in a vertical slice through the center of the sunspot. The umbral and penumbral locations are indicated by the (somewhat exaggerated) pedestals near x = 0. The horizontal size is derived from the ten days of data used (Nov. 14–23, 2013). The average umbral radius is 11.5 Mm and penumbral radius is 25.1 Mm. The solid curves are the two-skip ray paths for the range of one-skip distances Δ = 75–146 Mm used in the analysis. The dashed curves are the corresponding one-skip rays. The analysis consists of calculating temporal cross covariances between endpoints (e.g. A and B). For the curves drawn, an output map point would be associated with the location half way (C) between the endpoints, or at the center of the spot. By moving the endpoints in longitude and latitude, a map is constructed. The short vertical lines at ±36 Mm indicate the size of the map shown later in Figs. 2 and 5.

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