Fig. 1.

Possible pathways contributing to urban cloud formation. Urban–rural circulations advect moist air from the surrounding rural areas into the city and form a moisture convergence over the city. Thermal convection induced by surface heating combined with moisture convergence collectively transports moisture to a higher level in the atmosphere and enhances cloud occurrences over the city. Wind field changes due to urban surface roughness interacting with local urban buoyancy influence the convergence. Urban aerosol emission modifies cloud formation and properties.