Cloud Formation

A cloud is any visible mass of water droplets, ice crystals, or a mixture of both that is suspended in the air. Clouds are formed when relatively moist air rises and the lower pressures prevailing at higher levels allows it to expand. By expanding, the air cools adiabatically until its temperature falls below the dewpoint. At this point the air becomes saturated and water vapour condenses onto condensation nuclei which are microscopic particles in the air. Most condensation nuclei are produced by natural and man-made fires over land and by wave action over the oceans. Dust and soil particles blown into the atmosphere also are sources of nuclei

Clouds consist entirely of water droplets, entirely of ice crystals, or of a mixture of water droplets and ice crystals, with crystals predominating in the colder, upper regions of the troposphere. An entire lesson will be devoted to cloud types and their associated weather.