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 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 chemical composition and pulsation wave properties. Combination of magnetoacoustic tomography with the Doppler imaging of the horizontal non-radial pulsation pattern opens possibility for an unprecedented three-dimensional mapping of roAp atmospheres