Atmospheric clouds are dynamic systems consisting of cloud and precipitation particles falling at some terminal speed. Updrafts in the air reduce this downward descent and sometimes even reverse the direction of certain-sized cloud and precipitation particles. This dynamical nature plays a decisive role in the processes involving phase transitions and particle growth (such as melting, freezing, and evaporation), growth due to water vapor diffusion, growth arising out of collision-coalescence, as well as gas and aerosol particle scavenging by cloud and precipitation particles.