Today it is known that clouds cover about 40% of a surface of the globe and are a receptacle of huge mass of water, at the same time 2/3 all cloudy covers exist in the field of low temperatures. Knowledge of the processes leading to formation of overcast and, as a result, loss of precipitation are important not only for meteorologists. The overcast influences a radio communication, a radar-location, aircraft, hydro- and to an agricultural technician and even astronautics. All this led to the fact that in the forties last century of the physicist of clouds became independent science.
Scientists traditionally divide clouds into warm and cold, i.e. existing at positive and at negative temperatures. Warm clouds are similar to fogs and consist of microscopic drops of water. As for cold clouds, according to traditional representations, they may contain the overcooled water drops, ice crystals or both the first, and the second at the same time, i.e. to be mixed on a phase.
In the theory, at emergence in a drop cloud of crystals of ice, Berzherona-Findayzen's process which is characterized perekondensation or phase distillation instantly begins. In other words, there is a vapor condensation in ice. It follows from this that the two-phase cloud is not capable to exist long. In a few minutes it turns into steady crystalline state. However researches of the outstanding scientist A.M. Borovikov, showed that in nature the mixed and drop cold clouds meet more often and exist much longer, than it is predicted by the theory, or laboratory practice shows.
In the conditions of a midland layered clouds are the most frequent and steady. They give also the greatest number of precipitation. Modern researches showed that practically all cold clouds are mixed, i.e. contain at the same time both drops of the overcooled water and ice crystals.
On structure they are divided into 3 basic types. The cold clouds which are traditionally considered as water belong to the first structural type. Researches showed that they contain ice crystals, not distinguishable by usual methods – their sizes less than 20 microns. Two other types of clouds are called ldosoderzhashchy. One of types is characterized by existence of rather large ice crystals which sizes exceed 200 microns. Usually it is the translucent cloud structures located at big height and not always noticeable from the earth. Other type of ldosoderzhashchy clouds is characterized by existence of small pieces of ice which sizes less than 20 microns. These are dense, opaque structures, by the form a little different from cold water and warm clouds. They most often bring precipitation in the form of snow or a rain, depending on temperature of a near-earth air bed. Existence of the liquid overcooled drops at temperatures is lower - 40 wasps, is explained by the fact that in real cloud structures water changes the physical and chemical properties. The volatility of water, in comparison with usual conditions, increases by 5 times. Such water evaporates and condensed much quicker than usual.