Résumé
Red supergiant stars (RSG) constitute a key-phase in the evolution of massive stars, characterized by strong mass loss of unknown origin. On-going radiative hydrodynamics (RED) simulations of these stars with (COBOLD)-B-5 show a peculiar convection pattern, with giant cells. We present high-resolution, multi-epoch spectroscopy of a sample of RSG, which provides a diagnostic of their atmospheric dynamics. We show synthetic spectra based on 3D RHD models. We suggest that convective motions axe important in the generation of the observed mass-loss rates.