2D maps of coherence between the time series at the initial seed location (identified by the cyan asterisk in Fig. 1) and at surrounding locations at different heights viz. (a) 1500 km, (b) 1000 km, (c) 500 km and (d) 250 km above the mean solar surface. The plotted region corresponds to the dashed square in the rightmost panel of Fig. 1. Left, middle, and right columns correspond to average coherence in the frequency range of 2–5 mHz, 6–10 mHz, 20–25 mHz, respectively.