Radial profile of the η parameter (black curve, left vertical axis) which expresses the difference between the sub-Keplerian gas velocity and the Keplerian velocity, v_θ = (1 − η)v_K. Initial radial profile of the dominant Stokes number τ_d (blue dashed curve, right vertical axis) which characterises aerodynamic properties of pebbles prevalent in the size-frequency distribution of solid particles.