Water Condensation Processes in Atmospheric Air

Abstract

Cloud properties and cloud processes are analyzed in this chapter. Clouds consisting of water microdroplets are formed in atmospheric condensation processes and partake in the water circulation through the atmosphere where water evaporates from the land or oceans and returns to the Earth’s surface in the form of precipitations mostly. Because of a restricted humidity of the standard atmosphere at any altitudes, water condensation proceeds there under the action of vertical winds which mix low wet layers of the atmosphere with cold high ones. The mechanisms of the formation and growth of water microdroplets in the atmosphere include processes of evaporation of water molecules from microdroplets, attachment of free water molecules to them, coagulation and coalescence processes, and gravitation growth of droplets which fall down under the action of their weight. Usually, kinetics of the growth of water microdrops in clouds results from the competition between the coalescence and gravitation growth mechanisms. A high density of free and bound water molecules is realized in cumulus clouds where, due to the equilibrium between free water molecules and microdroplets which is established fast, the number density of free water molecules is equal to that at the saturated vapor pressure. In addition, the transformation of neutral microdroplets in water drops of precipitation proceeds fast compared with the lifetime of cumulus clouds. Hence, water microdroplets are charged in cumulus clouds and their charges have the same sign. Thus, processes of growth of water droplets in cumulus clouds proceed simultaneously with electric processes. As a result, processes of growth of water microdrops in cumulus clouds are connected with atmospheric electricity.