Observations of pulsations in roAp stars

I review recent results of the observations of magnetoacoustic p-mode oscillations in roAp stars with the focus on time-resolved spectroscopic studies. Time-series spectroscopy of roAp stars reveals unexpected and diverse pulsational behaviour in the spectral lines of different chemical elements. These unique pulsational characteristics arise from an interplay between the short vertical length of pulsation waves and extreme chemical stratification in the atmospheres of peculiar stars. This enables a tomographic reconstruction of the depth-dependence of the chemical composition and pulsation wave properties. The combination of magnetoacoustic tomography with Doppler imaging of the horizontal non-radial pulsation pattern opens the possibility for an unprecedented three-dimensional mapping of roAp star atmospheres.