Dependence of the Rayleigh-Taylor instability on the speed of sound reduction rate with ξ = const. (panel a) and C_max = const (panel b). Each panel shows the maximum amplitude of the y-component of the velocity at time = 2.5 with PVS form (red with diamond) and PMS form (blue with cross). The horizontal dashed line shows the reference simulation results without the RSST (ξ = 1) in 4096 × 4096 grids.