Snapshots of granular convection at the surface for the simulations without magnetic field and with a horizontal resolution of 12.5 km: temperature (left column) and density (right). The black square indicates a large whirlpool, the horizontal and vertical structure of which are shown in panels (c)–(f). Black arrows show the flow velocity. White arrows in panel (b) point to the centers of some vortices (dark low-density points).