Profiles with different strengths of turbulence. Upper panel: planetesimal surface density with Disc A and Ṁ_peb = 10⁻⁴ M_E yr⁻¹. Lower panel: snapshots of the pebble-to-gas density ratio on the mid-plane with the same condition at t = 3.0 × 10⁵, 3.8 × 10⁵, and 4.0 × 10⁵ yr. The purple, green, light blue, and orange plots represent the profiles with α = 3 × 10⁻⁴, 10⁻³, 3 × 10⁻³, and 10⁻². The dotted line in the upper panel indicates the estimated planetesimal surface density by Eq. (21). No planetesimals form with α = 10⁻². The dotted lines in the lower panel indicate the unperturbed pebble-to-gas density ratios on the mid-planes (Eq. (20)). The black line in the lower panel represents where the ratio is unity.