Radial profiles of the drift velocity of the gas, the surface density Σ of the gas, and νΣ for the model without irradiation (top) and with irradiation (bottom). The plots are shown for disc #1 (Σ₀ = 95.8 g cm^-2, a_core = 46 AU, γ = 0.9) at the beginning (red line) and the end (green line) of the simulations (t = 10 Myr). The peak of v_drift at ~20 AU for the model without irradiation arises because Σ has reached its lowest value.