DROP SIZE SEPARATION IN NUMERICALLY SIMULATED CONVECTIVE CLOUDS AND ITS EFFECT ON WARM RAIN FORMATION

It is shown that, as a result of the flow diffluence at the upper leve ls of the cloud, droplets of different sizes move along different traj ectories. The small droplets with negligible fall velocities will have higher probability of being carried away from the cloud and completel y evaporating, while the droplets with larger fall velocities are more likely to be recycled in the cloud. During the recycling process drop lets of different sizes reenter the cloud at different spatial locatio ns and mix with the droplet-free air brought from the upper levels of the cloud. This results in the decrease of the total concentration, as well as in the concentration of larger droplets, thus facilitating ra in formation through enhanced condensational growth. It is also shown that the notion of an air parcel as an entity containing various const ituents (water vapor, aerosol particles, cloud droplets, etc.), all ev olving under the same dynamical conditions, may be rather limited. Our results indicate that these elements may have quite different histori es resulting in inhomogeneities in cloud microstructure.