(color online) Spatial distributions of dusty vortices in the horizontal plane at gas pressures of (a) 30 Pa, (b) 40 Pa, (c) 50 Pa, (d) 60 Pa, (e) 90 Pa, with rf power fixed at 15 W, and (f) trajectories of grains in a slant (e). Circles indicate the starting points of the trajectories.