Temporal progression of the los Doppler transient during the impulsive phase of the flare. Panel (a) shows the raw-preflare Doppler signature. Panels (b), (c), and (d) show the transient component of the succeeding Doppler signatures at 45 s intervals. Closed curves mark the locations of the acoustic sources mapped in Figure 2(b). Positive values attached to color bars indicate redshift, i.e., velocities with los components away from the observer, in units of km s⁻¹.