Turbulent Transport Mechanism in the Roughness Sublayers over Idealized Urban Areas and Its Implication to Street-Level Ventilation

•Use drag coefficients to elucidate the transport mechanism in the RSLs over urban areas.•Aerodynamic resistance of roughness elements enhances RSL transport efficiency.•RSL streamwise and vertical winds are more correlated, promoting mixing and transport.•Surface-mounted roughness elements strengthen the AM and FM of RSL motion scales.•Rougher the aerodynamic resistance is, weaker (stronger) the TKE production (entrainment).