Air

Cloud formation

Cloud formation is apparently a very simple process, caused by the condensation of atmospheric humidity into drops of water, but in actual fact it is a more complex phenomenon, in which different factors and mechanisms are involved. All the processes however are based on the ascent of a mass of humid air and its successive cooling up to dew point. In this process a body of water or the humidity of the ground evaporate as a result of solar radiation and a volume of hot, humid air forms and slowly starts to rise since hot, humid air is lighter than the air surrounding it. As it rises two factors act on the mass of air: the decrease in pressure makes the air expand and the decrease in temperature, due to the higher altitude, cools it until it reaches dew point: the air mass is saturated with water vapour and this condenses into small drops of water in its liquid state. A cloud is the visible expression of this process. The condensation process is favoured if particles and impurities are present that can act as condensation nuclei on which the droplets can deposit. If these are absent, the air mass can become over-saturated with water vapour.