Around 1940 cloud physics appeared as a new meteorological discipline, concentrating mostly on cloud microphysics, which is the study of how the cloud particles form. Mason (1957) soon realised, however, that cloud microphysics was only part of the subject and that another, which can be termed cloud dynamics, needed to be added. This concerned the motion of the atmosphere involved in cloud formation, from the small scale of a kilometre or less to over 1000 km. Cloud dynamics was much more difficult to investigate than microphysics because of its large scale and because of the lack of suitable tools at the time. But with the advent of radar, specialised aircraft, satellite imagery and computers with numerical modelling techniques it has become possible to identify most of the important air movements associated with all cloud types. However, it is not possible in one chapter to include the very detailed knowledge now available on this, and just sufficient will be said to provide a background to the formation of clouds. The formation of cloud droplets or ice crystals and the formation, from them, of raindrops, hail and snow are dealt with in the next chapter.

Cloud classification and identification

In the uncomplicated situation, the identification of clouds is straightforward, but it can be quite difficult if there are several types co-existing at the same time. Also one type can change into another, leading to halfway stages possibly causing one to be confused with another.