Precipitation (meteorological, liquid and solid bodies that)

PRECIPITATION, meteorological, liquid and solid bodies that separate from the air onto the surface of the soil and solid objects due to the condensation of water vapor contained in the atmosphere. If precipitation falls from a certain height, rain, hail, and snow are produced; if they form in the lowest layer of the atmosphere, dew and frost are produced. With the simultaneous falling of supercooled raindrops and the condensation of water vapor on the surface of solid objects, glaze ice is produced. All precipitation increases the water supply on the earth's surface at the expense of the water vapor contained in the air. The amount of precipitation is expressed by the thickness (in mm) of the layer of water that would form on a horizontal surface if it did not absorb moisture. To measure the amount of precipitation, a rain gauge with a circular opening with an area of 500 cm² is used, such that 50 cm³ of water forms a layer 1 mm thick in it. The amount of precipitation fluctuates in various places on earth in very significant ranges and depends on the geographical latitude of the locality, the time of year, prevailing winds, soil relief, etc. Regarding the distribution of precipitation, Europe can be divided into 1) the region of autumn and winter precipitation, covering countries located along the southern and western shores of Europe, and 2) the region of summer rains, lying inside the continent. Such a distribution depends primarily on the different relationships between the temperature of the sea and land in winter and summer. The amount of precipitation in Europe decreases as one moves away from the ocean to the east and north, and this decrease is especially pronounced near the ocean shores. Usually, the annual amount of precipitation in a given locality is determined, but it cannot give an idea of the raininess of a given locality, since one heavy downpour provides a greater amount of precipitation than a light rain continuing for several days in a row. Thus, to assess the climate of a locality, it is important to know the number of rainy days in a year and in different seasons. A single heavy rain has a useful hygienic significance, cleaning the air of dust, whereas a light, prolonged rain deprives patients of the opportunity to use the open air and the rays of the sun. A rainy day is considered a day in which at least 0.1 mm of precipitation has fallen. The annual number of rainy days in Europe increases from south to north, while the amount of precipitation, conversely, decreases. By dividing the annual amount of precipitation by the number of rainy days in a year, one obtains the intensity of precipitation or the average amount of precipitation falling in 1 rainy day. For Europe, this intensity of precipitation equals 4–6 mm. The intensity of individual rains is determined by the amount of water falling per unit of time; a downpour is called a rain that gives more than 0.5 mm of water in 1 minute. Everything said above also applies to snow. The average density of snow is 0.1, i.e., 10 times less than the density of water. The lower the air temperature, the finer the snowflakes. At an air temperature above 0°, snowflakes are large and loose, because they are saturated with water. Snow protects the soil from cooling. The appearance of dew and frost is explained by the cooling of the earth's surface due to nocturnal radiation into interplanetary space. Dew forms more in quiet and clear nights, because with wind, the air is carried away before it has time to cool. Frost differs from dew only in that the deposition of moisture occurs at a temperature below 0°. A detailed study of the distribution and intensity of precipitation is of great interest for using the climate of any locality for prophylactic and therapeutic purposes; in particular, this is significant for health resorts.

A. Lozinsky. Bibliography—see bibliography for the articles Climate and Meteorology.