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tokens: 2009 , 2010 ; Lyra Klahr 2011 ; Lyra 2013 ). Yet it remains 2–3 orders of magnitude lower than the radial and azimuthal velocity components Figure 3 . Figure 1. Vertical vorticity of unstratified gas in a three-dimensional box at different times. The convective overstability amplifies seed noise into growing vortices, that intensify and merge viscously, saturating at radial length similar to the pressure scale height. Figure 2. The vertical component of the vorticity () in the midplane (left panels) and a vertical cut through the disk at the azimuthal location of maximum negative vorticity (indicated by the dashed line). Also shown is the vertical velocity component ( u z ). The upper plots are shown at 100 local orbits (top panels). At this time, there is no structure in the vertical direction: the flow is essentially two-dimensional. After 275 local orbits (bottom panels) there is now turbulent motion inside the vortex, which is also visible in the vertical velocity. This is an indication of the growth of elliptical instability in the vortex cores. Figure 3. Gas velocity components averaged over the entire box. As the elliptical instability sets in, the vertical velocity component (green line) increases steeply, while staying well below the azimuthal and radial components. 4.1. Pebble Evolution We first discuss the run without baroclinic driving. As expected, the pebbles settle to the midplane, soon triggering the streaming instability. Although we assumed an overall initial dust-to-gas ratio of , the initial dust-to-gas ratio in the midplane is already and increases even further as the sedimentation progresses. The maximum dust-to-gas ratio of the simulation with pebbles and without baroclinic driving can be seen in Figure 4 (red line). The other two lines in the plot show the maximum dust-to-gas ratios for the simulation with , (green line), and pebbles (black line). Figure 4. Maximum dust-to-gas ratio for simulations with (black line) and (green and red line) pebbles. indicates that no baroclinic feedback was included in the simulation. Although the high pebble concentration in the simulations with baroclinic effects disrupts the vortex in the midplane, where pebbles are located, the maximum dust-to-gas ratio is higher than without baroclinic effects. The maximum concentration for with baroclinic driving is only a factor of 2 higher than in the case without it. Inspecting the evolution of the dust density in the baroclinic simulation, we see that, as expected, the pebbles settle to the midplane and get trapped in the vortices. Yet, after only three orbits, the pebbles start to perturb the vortices in the midplane via the streaming instability. Like in the 2D simulations of Raettig et al. ( 2015 ), high pebble densities generate local perturbations of the velocity field visible as steep vorticity gradients. Figure 5 shows the vorticity at the top of the box (left panel) and in the midplane (middle panel), and the dust-to-gas ratio in the