Time evolution of the vertical velocities of the columns at location A during the propagation of shock waves (a) and at location B in the network region (b). Upward motion, away from the photosphere, is indicated by negative velocity (blue). The representative formation heights of the lower and upper components of the observables for bands 3 and 6 are marked by the solid and dashed lines, respectively (see Sect. 3 in the main text for details).