Abstract
Not all cumulus clouds can vent mixed-layer air into the free atmosphere. Therefore, three subtypes of fair-weather cumulus clouds are identified based on the nature of their interaction with the mixed layer: forced, active and passive clouds. Forced clouds, the visible tracers within the tops of some mixed-layer thermals, are totally embedded within the mixed layer. Active clouds reach above their level of free convection and are responsible for inhibiting mixed-layer growth and for venting pollutants from the mixed layer. Passive clouds are the decaying remnants of formerly active clouds, and are disconnected from the mixed layer.
