Density (top panel) and velocity (bottom panel) at five different times during the evolution of a linear (solid line) and weakly nonlinear (dashed line) perturbation representing an idealised CW. The incoming wave (red) steepens into a shock in the nonlinear regime. The reflected wave at the interface between region 1 and region 2, which represents the CH boundary (located at x = 0) is a rarefaction wave (black) while the transmitted (blue) is a shock wave.