Cloud has been defined as a visible aggregation of minute water droplets and/or ice particles in the air, usually above the general ground level. Clouds are the most important form of suspended water droplets caused by condensation.
According to Critchfield, clouds are the condensation or sub-limitation forms that usually result from lifting processes. Blair is of the view that by far the most important cause of clouds is the adiabatic cooling resulting from the upward movement of air.
Sometimes mixing of warmer and cooler air also produces clouds. Trewartha is of the opinion that the one process that can reduce the temperature of deep and extensive masses of air enough to bring about cloud condensation is the expansion associated with the rising air currents, i.e., adiabatic cooling.
As more and more water vapour is condensed within an air mass, water droplets multiply, some of the sun’s light is blocked, and the visible result is a cloud.
Clouds are meteorologically significant in various ways. All precipitation occurs from clouds. We do not get precipitation from all clouds, but there can be no precipitation without clouds. Clouds also play an important role in the heat energy budget.
This is because clouds absorb a part of the incoming solar radiation. They reflect some of the incoming solar radiation back to space and also diffuse some of it. Clouds also absorb a part of terrestrial radiation and then re-radiate it back to the surface.
Another important point about clouds is that like a black body they radiate heat continuously in proportion to their temperatures. In the absence of clouds, days would have been much warmer and nights much colder.
During summer months cloudy days are cooler than the days without clouds. Similarly in winter a deck of thick clouds makes the nights warmer and less chilly.
As we all know, convectional currents are limited to the troposphere only, and so this part of the atmosphere contains all clouds.
Clouds are of continual interest to the meteorologist, since they tell him what is going on in the atmosphere much above the earth’s surface.
They are deemed as useful indicators of various meteorological processes. The importance of clouds in aviation cannot be overemphasized. Low clouds may make landings and takeoffs difficult.