Time-slices showing umbral flashes and running waves observed in difference maps (unfiltered − filtered) of the Ca II line-centre intensity (left) and Doppler velocity (right). The slices are constructed along the cuts in x (top) and y (bottom) directions displayed in Fig. 5. White lines mark edges of the umbra, black lines the borders of the light bridge. The grey scale of Doppler velocities ranges from −2 to 2 km s^-1.