Perturbations of the absolute value of the radial velocity in the inwardly propagating pulse of compression, as a function of the radial position r. Different colours (thickness) correspond to two different initial amplitudes of the pulse. The red (thick) curves correspond to the instants of time t = 0.3 s (solid), t = 0.5 s (dotted), and t = 0.7 s (dashed). The blue (thin) curves correspond to t = 0.5 s (solid), t = 0.8 s (dotted), and t = 1.1 s (dashed). The spatial coordinate is measured in units of r₁.