Panels a–g: time distance map of slits 1−7 (see upper right panel of Fig. 1), respectively in AIA 193 Å. Panels h–n: minimum intensity points of corresponding time distance map of panels a–g, respectively, marked with black asterisks. The damped exponential sinusoidal fit is depicted by red solid lines. The green dashed lines are drawn to estimate the extent of the damped exponential sinusoidal fit.