Evaporation of water vapor, its transport and condensation in the atmosphere, the formation of clouds and precipitation are a single complex climate-forming moisture exchange process, as a result of which there is a continuous transition of water from earth surface into the air and from the air back to the earth's surface. Precipitation is an essential component of this process; they, along with air temperature, play a decisive role among those phenomena that are united by the concept of "weather".

Atmospheric precipitation is called the moisture that has fallen to the surface of the Earth from the atmosphere. Atmospheric precipitation is characterized by the average amount per year, season, individual month or day. The amount of precipitation is determined by the height of the water layer in mm, formed on a horizontal surface from rainfall, drizzle, heavy dew and fog, melted snow, crust, hail and snow pellets in the absence of seepage into the ground, surface runoff and evaporation.

Atmospheric precipitation is divided into two main groups: falling out of clouds - rain, snow, hail, cereal, drizzle, etc .; formed on the surface of the earth and on objects - dew, frost, drizzle, ice.

Precipitation of the first group is directly related to another atmospheric phenomenon - cloudy, which plays a critical role in the temporal and spatial distribution of all meteorological elements. Thus, clouds reflect direct solar radiation, reducing its arrival at the earth's surface and changing the lighting conditions. At the same time, they increase scattered radiation and decrease effective radiation, which contributes to an increase in absorbed radiation.

Changing the radiation and thermal regime of the atmosphere, clouds have big influence on vegetable and animal world, as well as on many aspects of human activity. From an architectural and construction point of view, the role of clouds is manifested, firstly, in the amount of total solar radiation entering the development area, to buildings and structures and determining their thermal balance and natural illumination regime internal environment... Secondly, the phenomenon of cloudiness is associated with precipitation, which determines the humidity regime of the operation of buildings and structures, which affects the thermal conductivity of the enclosing structures, their durability, etc. Thirdly, the fallout of solid precipitation from clouds determines the snow loads on buildings, and hence the shape and structure of the roof and other architectural and typological features associated with snow cover... Thus, before proceeding to the consideration of precipitation, it is necessary to dwell in more detail on such a phenomenon as cloudiness.

Clouds - these are accumulations of condensation products (droplets and crystals) visible with a simple eye... According to the phase state of cloud elements, they are divided into aquatic (drip) - consisting only of drops; icy (crystalline)- consisting only of ice crystals, and mixed - consisting of a mixture of supercooled drops and ice crystals.

Cloud shapes in the troposphere are very diverse, but they can be reduced to a relatively small number of basic types. This "morphological" classification of clouds (ie, classification by their appearance) arose in the 19th century. and is generally accepted. According to her, all clouds are divided into 10 main genera.

In the troposphere, three layers of clouds are conventionally distinguished: upper, middle and lower. Cloud bases top tier are located in polar latitudes at altitudes from 3 to 8 km, in temperate latitudes - from 6 to 13 km and in tropical latitudes- from 6 to 18 km; middle tier respectively - from 2 to 4 km, from 2 to 7 km and from 2 to 8 km; lower tier at all latitudes - from the earth's surface up to 2 km. The upper tier clouds include feathery, cirrocumulus and cirrostratus. They are composed of ice crystals, translucent and shade little sunlight. In the middle tier there are altocumulus(drip) and highly layered(mixed) clouds. The lower tier contains layered, layered rain and stratocumulus clouds. Nimbostratus clouds are composed of a mixture of droplets and crystals, the rest are drip. In addition to these eight main types of clouds, there are two more, the bases of which are almost always in the lower tier, and the tops penetrate into the middle and upper tier, this is cumulus(drip) and cumulonimbus(mixed) clouds called clouds of vertical development.

The degree to which clouds cover the firmament is called cloudy. Basically, it is determined "by eye" by an observer at meteorological stations and is expressed in points from 0 to 10. At the same time, the level of not only the general, but also the lower cloudiness, which includes the clouds of vertical development, is set. Thus, cloudiness is written in the form of a fraction, in the numerator of which is the total cloudiness, in the denominator - the lower cloud.

Along with this, cloudiness is determined using photographs obtained from artificial satellites Earth. Since these photographs are taken not only in the visible, but also in the infrared range, it is possible to estimate the amount of clouds not only during the day, but also at night, when ground-based observations of clouds are not carried out. Comparison of ground-based and satellite data shows good agreement, with the largest differences being observed over continents and amounting to about 1 point. Here, ground-based measurements, due to subjective reasons, somewhat overestimate the amount of clouds in comparison with satellite data.

Summarizing long-term observations of cloudiness, we can draw the following conclusions regarding its geographical distribution: on average for the entire globe, cloud cover is 6 points, while over the oceans it is more than over the continents. The amount of clouds is relatively small at high latitudes (especially in Southern hemisphere), with decreasing latitude it grows and reaches a maximum (about 7 points) in the belt from 60 to 70 °, then towards the tropics the cloudiness decreases to 2-4 points and again increases with approaching the equator.

In fig. 1.47 shows the total cloud cover on average for the year for the territory of Russia. As can be seen from this figure, the amount of clouds on the territory of Russia is distributed rather unevenly. The most cloudy are the north-west of the European part of Russia, where the amount of total cloud cover on average per year is 7 points or more, as well as the coast of Kamchatka, Sakhalin, the north-western coast of the Sea of ​​Okhotsk, the Kuril and Commander Islands. These areas are located in areas of active cyclonic activity, characterized by the most intense atmospheric circulation.

Eastern Siberia, except for the Central Siberian Plateau, Transbaikalia and Altai, is characterized by a lower average annual amount of clouds. Here it is in the range from 5 to 6 points, and in the extreme south in some places it is even less than 5 points. This entire relatively low-cloud region of the Asian part of Russia is in the sphere of influence of the Asian anticyclone, therefore, it is characterized by a low frequency of cyclones, which are mainly associated with a large number of clouds. A stripe of less than significant amount clouds, elongated in the meridional direction directly behind the Urals, which is explained by the "shading" role of these mountains.

Rice. 1.47.

Under certain conditions, the clouds fall out precipitation. This happens when some of the elements that make up the cloud become larger and can no longer be held by vertical air currents. The main and necessary condition for heavy precipitation is the simultaneous presence of supercooled drops and ice crystals in the cloud. These are altostratus, nimbostratus and cumulonimbus clouds, from which precipitation falls.

All sediments are divided into liquid and solid. Liquid precipitation - it is rain and drizzle, they differ in the size of the drops. TO solid sediments include snow, sleet, grains and hail. The amount of precipitation is measured in mm of the precipitated water layer. 1 mm of precipitation corresponds to 1 kg of water dropped out on an area of ​​1 m 2, provided that it does not drain, evaporate and is not absorbed by the soil.

By the nature of precipitation, precipitation is divided into the following types: heavy precipitation - uniform, long-lasting, fall out of stratus clouds; heavy rainfall - characterized by a rapid change in intensity and short duration, they fall out of cumulonimbus clouds in the form of rain, often with hail; drizzling precipitation - in the form of drizzle fall out of stratus clouds.

Daily variation of precipitation it is very complex, and even in long-term averages it is often impossible to find any regularities in it. However, two types stand out daily rate precipitation - continental and nautical(coastal). The continental type has two highs (in the morning and afternoon) and two lows (at night and before noon). Marine type characterized by one maximum (at night) and one minimum (during the day).

The annual course of precipitation is different at different latitudes and even within the same zone. It depends on the amount of heat, thermal regime, air circulation, distance from the coast, the nature of the relief.

The most abundant precipitation in equatorial latitudes ah, where their annual number exceeds 1000-2000 mm. On the equatorial islands of the Pacific Ocean the rainfall is 4000-5000 mm, and on the windward slopes of tropical islands - up to 10 000 mm. Heavy rainfall is caused by powerful ascending currents of very humid air. To the north and south of the equatorial latitudes, the amount of precipitation decreases, reaching a minimum at latitudes 25-35 °, where the average annual value does not exceed 500 mm and decreases in the inland regions to 100 mm or less. In temperate latitudes, the amount of precipitation increases slightly (800 mm), again decreasing towards high latitudes.

The maximum annual precipitation was recorded in Cher-rapunji (India) - 26 461 mm. The minimum recorded annual precipitation is in Aswan (Egypt), Iquique - (Chile), where in some years precipitation does not fall at all.

By origin, convective, frontal and orographic sediments are distinguished. Convective precipitation typical for the hot zone, where heating and evaporation are intense, but in summer they are often in temperate... Frontal precipitation is formed when two air masses meet with different temperatures and other physical properties. They are genetically associated with cyclonic eddies typical of extratropical latitudes. Orographic sediments fall on the windward slopes of mountains, especially high ones. They are abundant if the air comes from the warm sea and has a high absolute and relative humidity.

Measurement methods. To collect and measure precipitation, use following devices: Tretyakov's precipitation gauge, total siege-comer and pluviograph.

Rain gauge Tretyakov serves to collect and subsequently measure the amount of liquid and solid precipitation that fell over a certain period of time. It consists of a cylindrical vessel with a receiving area of ​​200 cm 2, a strip cone-shaped protection and a tagan (Fig. 1.48). The kit also includes a spare jar and lid.

Rice. 1.48.

Receiving vessel 1 is a cylindrical bucket, barred by a diaphragm 2 in the form of a truncated cone, into which a funnel with a small hole in the center is inserted in summer to reduce evaporation of precipitation. There is a spout for draining the liquid in the vessel 3, resealable 4, soldered on chain 5 to the vessel. The vessel installed on the tagan 6, surrounded by a cone-shaped strip protection 7, consisting of 16 plates curved in a special pattern. This protection is necessary to prevent snow from blowing out of the gauge in winter and raindrops in high winds in summer.

The amount of precipitation that fell during the night and daytime half of the day is measured in the periods closest to 8 and 20 hours of standard (winter) time. At 03 and 15 h UTC (universal time coordinated - UTC) in I and II time zones, the main stations also measure precipitation using an additional precipitation gauge, which must be installed at the meteorological site. For example, in the meteorological observatory of Moscow State University, precipitation is measured at 6, 9, 18 and 21 hours of standard time. To do this, the measuring bucket, after having closed it with a lid, is taken into the room and water is poured through the spout into a special measuring glass. To each measured amount of precipitation, a correction for the wetting of the sediment-collecting vessel is added, which is 0.1 mm if the water level in the measuring glass is below half of the first division, and 0.2 mm if the water level in the measuring glass is in the middle of the first division or higher.

The solid sediments collected in the collection vessel must melt before measurement. For this, the vessel with sediments is left in a warm room for some time. In this case, the vessel should be closed with a lid, and the spout with a cap in order to avoid evaporation of precipitation and deposition of moisture on the cold walls from the inside of the vessel. After the solid sediments have melted, they are poured into a precipitation beaker for measurement.

In uninhabited, hard-to-reach areas, it is used total precipitation gauge M-70, intended for collection and subsequent measurement of precipitation that fell over a long period of time (up to a year). This rain gauge consists of a receiving vessel 1 , reservoir (sediment collector) 2, foundations 3 and protection 4 (Fig. 1.49).

The receiving area of ​​the rain gauge is 500 cm 2. The reservoir consists of two detachable cone-shaped parts. For a tighter connection of the parts of the tank, a rubber gasket is inserted between them. The collecting vessel is fixed in the opening of the reservoir

Rice. 1.49.

on the flange. The reservoir with the receiving vessel is mounted on a special base, which consists of three struts connected by spacers. The protection (against the blowing of precipitation by the wind) consists of six plates, which are fixed to the base by means of two rings with clamping nuts. The upper edge of the protection is in the same horizontal plane with the edge of the receiving vessel.

To protect the precipitation from evaporation, mineral oil is poured into the reservoir at the installation site of the precipitation gauge. It is lighter than water and forms a film on the surface of accumulated sediments that prevents their evaporation.

Liquid precipitates are selected using a rubber bulb with a tip, solid ones are carefully broken up and selected with a clean metal mesh or spatula. Determination of the amount of liquid precipitation is carried out using a measuring glass, and solid - by means of a balance.

For automatic recording of the amount and intensity of liquid atmospheric precipitation apply pluviograph(fig. 1.50).

Rice. 1.50.

The pluviograph consists of a body, a float chamber, a forced drain mechanism and a siphon. The receiver of sediments is a cylindrical vessel / with a receiving area of ​​500 cm 2. It has a cone-shaped bottom with holes for water drainage and is mounted on a cylindrical body 2. Sediments through drain pipes 3 and 4 fall into a recording device consisting of a float chamber 5, inside which there is a moving float 6. An arrow 7 with a feather is fixed on the float rod. The recorded precipitation is made on a tape worn on the drum of the clockwork. 13. A glass siphon 9 is inserted into the metal tube 8 of the float chamber, through which water from the float chamber is drained into a control vessel 10. A metal sleeve is mounted on the siphon 11 with clamping sleeve 12.

When sediment flows from the receiver into the float chamber, the water level in it rises. At the same time, the float rises up, and the pen draws a curved line on the tape - the steeper, the greater the intensity of precipitation. When the amount of precipitation reaches 10 mm, the water level in the siphon tube and the float chamber becomes the same, and water spontaneously drains into the bucket 10. In this case, the pen draws a vertical straight line on the tape from top to bottom to zero; in the absence of precipitation, the pen draws a horizontal line.

Typical values ​​of the amount of precipitation. To characterize the climate, average amounts are calculated or precipitation amount for certain periods of time - month, year, etc. It should be noted that the formation of precipitation and their amount in any territory depend on three main conditions: the moisture content of the air mass, its temperature and the possibility of ascent (rise). These conditions are interrelated and, acting together, create a rather complex picture of the geographical distribution of precipitation. Nevertheless, the analysis of climatic maps makes it possible to identify the most important patterns of precipitation fields.

In fig. 1.51 presents the average long-term amount of precipitation falling per year on the territory of Russia. It follows from the figure that on the territory of the Russian Plain, the greatest amount of precipitation (600-700 mm / year) falls in the zone of 50-65 ° N. It is here that cyclonic processes are actively developing throughout the year and the largest amount of moisture is transferred from the Atlantic. To the north and south of this zone, the amount of precipitation decreases, moreover, south of 50 ° N latitude. this decrease occurs from northwest to southeast. So, if on the Oka-Don plain falls 520-580 mm / year, then in the lower reaches of the river. On the Volga, this amount is reduced to 200-350 mm.

The Urals significantly transforms the precipitation field, creating a meridionally elongated strip of increased amounts on the windward side and on the tops. At some distance behind the ridge, on the contrary, there is a decrease in the annual amount of precipitation.

Similar to the latitudinal distribution of precipitation in the Russian Plain on the territory of Western Siberia in the 60-65 ° N zone. there is a zone of increased precipitation, however, it is narrower than in the European part, and less precipitation falls here. For example, in the middle course of the river. Ob, the annual precipitation is 550-600 mm, decreasing towards the Arctic coast to 300-350 mm. Almost the same amount of precipitation falls in the south of Western Siberia. At the same time, in comparison with the Russian Plain, the area of ​​low precipitation is significantly shifted to the north.

As we move eastward, deeper into the continent, the amount of precipitation decreases, and in a vast basin located in the center of the Central Yakutsk Lowland, closed by the Central Siberian Plateau from westerly winds, the amount of precipitation is only 250-300 mm, which is typical for steppe and semi-desert regions of more southern latitudes. Further to the east, as we approach the marginal seas of the Pacific Ocean, the number

Rice. 1.51.

precipitation increases sharply, although the complex relief, different orientations of mountain ranges and slopes create a noticeable spatial heterogeneity in the distribution of precipitation.

Impact of precipitation on various sides economic activity a person is expressed not only in a more or less strong humidification of the territory, but also in the distribution of precipitation throughout the year. For example, hard-leaved subtropical forests and shrubs grow in areas where the average annual rainfall is 600 mm, and this amount falls in three winter months. The same amount of precipitation, but evenly distributed throughout the year, determines the existence of the zone mixed forests temperate latitudes. Many hydrological processes are also related to the nature of the intra-annual distribution of precipitation.

From this point of view, an indicative characteristic is the ratio of precipitation in the cold season to the amount of precipitation in the warm season. In the European part of Russia, this ratio is 0.45-0.55; in Western Siberia - 0.25-0.45; in Eastern Siberia - 0.15-0.35. The minimum value is noted in Transbaikalia (0.1), where the influence of the Asian anticyclone is most pronounced in winter. On Sakhalin and the Kuril Islands, the ratio is 0.30-0.60; the maximum value (0.7-1.0) is noted in the east of Kamchatka, as well as in the mountain ranges of the Caucasus. The prevalence of precipitation in the cold period over precipitation in the warm period is observed in Russia only on the Black Sea coast of the Caucasus: for example, in Sochi it is 1.02.

People are also forced to adapt to the annual course of precipitation, constructing various buildings for themselves. The most vividly regional architectural and climatic features (architectural and climatic regionalism) are manifested in the architecture of folk dwellings, which will be discussed below (see paragraph 2.2).

Influence of relief and buildings on the precipitation regime. The relief makes the most significant contribution to the nature of the precipitation field. Their number depends on the height of the slopes, their orientation in relation to the moisture-carrying flow, the horizontal dimensions of the hills and the general conditions of the region's humidification. Obviously, in mountain ranges, the slope oriented towards the moisture-carrying flow (windward slope) is irrigated more than the one protected from the wind (leeward slope). The distribution of precipitation in flat areas can be influenced by relief elements with relative heights of more than 50 m, thus creating three characteristic areas with different precipitation patterns:

• an increase in precipitation on the plain in front of the hill (“dam” precipitation);
• an increase in precipitation on the very hill;
• decrease in precipitation from the leeward side of the hill ("rain shadow").

The first two types of sediments are called orographic (Fig. 1.52), i.e. directly related to the influence of the terrain (orography). The third type of precipitation distribution is indirectly related to the relief: a decrease in precipitation occurs due to a general decrease in the moisture content of the air, which occurred in the first two situations. Quantitatively, the decrease in precipitation in the "rain shadow" is commensurate with the increase in precipitation on a hill; the amount of precipitation of "damming up" is 1.5-2 times higher than the amount of precipitation in the "rain shadow".

"Damming"

Windward

Rain

Rice. 1.52. Orographic sediment scheme

Influence major cities on the distribution of precipitation is manifested due to the presence of the effect of "heat island", increased roughness of the urban area and air pollution. Studies carried out in different physical and geographical zones have shown that inside the city and in the suburbs located on the windward side, the amount of precipitation increases, and maximum effect is noticeable at a distance of 20-25 km from the city.

In Moscow, the above patterns are expressed quite clearly. An increase in precipitation in the city is observed for all their characteristics, starting with the duration and ending with the provision of extreme values. For example, average duration precipitation (h / month) in the center of the city (Balchug) exceeds the duration of precipitation on the territory of the TSKhA as a whole for the year, and in any month of the year without exception, and the annual amount of precipitation in the center of Moscow (Balchug) is 10% more than in near suburb (Nemchinovka), located most time from the windward side of the city. For the purposes of architectural and urban planning analysis, the mesoscale precipitation anomaly that forms over the territory of the city is considered as a background for identifying smaller-scale patterns, which mainly consist in the redistribution of precipitation within buildings.

In addition to the fact that precipitation can fall from the clouds, it is also formed on the surface of the earth and on objects. These include dew, frost, drizzle and ice. Precipitation falling on the earth's surface and formed on it and on objects is also called atmospheric phenomena.

Dew - water droplets formed on the surface of the earth, on plants and objects as a result of contact of humid air with a colder surface at an air temperature above 0 ° C, a clear sky and calm or weak wind. As a rule, dew forms at night, but its appearance is possible in other parts of the day. In some cases, dew can be observed in haze or fog. The term dew is also often used in construction and architecture to refer to those parts of building structures and surfaces in an architectural environment where water vapor can condense.

Frost - white sediment crystalline structure, appearing on the surface of the earth and on objects (mainly on horizontal or slightly sloping surfaces). Frost appears when the surface of the earth and objects cools due to the radiation of heat by them, as a result of which their temperature drops to negative values. Hoarfrost is formed when the air temperature is below zero, with calm or weak wind and light cloudiness. Abundant deposition of frost is observed on grass, the surface of leaves of shrubs and trees, roofs of buildings and other objects that do not have internal sources of heat. Frost can also form on the surface of the wires, causing them to become heavier and to increase the tension: the thinner the wire, the less frost settles on it. Frost deposition on wires 5 mm thick does not exceed 3 mm. Frost does not form on threads less than 1 mm thick; this makes it possible to distinguish between frost and crystalline frost, the appearance of which is similar.

Rime - white, loose sediment of a crystalline or granular structure, observed on wires, tree branches, individual blades of grass and other objects in frosty weather in light winds.

Grainy rime formed as a result of freezing on objects of supercooled fog droplets. Its growth is facilitated by high speeds winds and mild frost (from -2 to -7 ° C, but it also happens at a lower temperature). Granular rime has an amorphous (non-crystalline) structure. Sometimes its surface is bumpy and even acicular, but the needles are usually matte, rough, without crystal edges. When in contact with a supercooled object, fog drops freeze so quickly that they do not have time to lose their shape and give a snow-like deposit, consisting of ice grains that are not visible to the eye (ice bloom). With an increase in the air temperature and the enlargement of fog droplets to the size of drizzle, the density of the formed granular frost increases, and it gradually turns into ice. With an increase in frost and a weakening of the wind, the density of the formed granular frost decreases, and it is gradually replaced by crystalline frost. Deposits of granular frost can reach dangerous sizes in terms of strength and preservation of the integrity of objects and structures on which it is formed.

Crystalline frost - white precipitate, consisting of fine ice crystals of fine structure. When settling on tree branches, wires, ropes, etc. crystalline frost looks like fluffy garlands that easily crumble when shaken. Crystalline frost is formed mainly at night with a cloudless sky or thin clouds at low air temperatures in calm weather, when there is fog or haze in the air. Under these conditions, frost crystals are formed by direct transition to ice (sublimation) of water vapor contained in the air. For the architectural environment, it is practically harmless.

Ice most often occurs when large drops of supercooled rain or drizzle fall and spread on the surface in the temperature range from 0 to -3 ° C and is a layer of dense ice that grows mainly from the windward side of objects. Along with the concept of "ice" there is a close concept of "ice". The difference between them is in the processes that lead to the formation of ice.

Ice - This is ice on the earth's surface, formed after a thaw or rain as a result of the onset of a cold snap, leading to freezing of water, as well as when rain or sleet falls on the frozen ground.

The impact of ice deposits is diverse and, first of all, is associated with the disorganization of the work of the energy economy, communications and transport. The radius of ice crusts on the wires can reach 100 mm or more, and the weight can be more than 10 kg per running meter. Such a load is destructive for wire communication lines, power transmission lines, high-rise masts, etc. For example, in January 1998, a strong ice storm swept through the eastern regions of Canada and the United States, as a result of which, in five days, a 10-centimeter layer of ice was frozen on the wires, causing numerous breaks. About 3 million people were left without electricity, and the total damage was $ 650 million.

In the life of cities, the condition of roads is also very important, which in case of icy conditions become dangerous for all types of transport and passers-by. In addition, the ice crust causes mechanical damage to building structures - roofs, cornices, facade decor. It contributes to freezing, eradication and death of plants present in the urban greening system, and degradation natural complexes that are part of the urban area, due to lack of oxygen and excess carbon dioxide under the ice shell.

In addition, atmospheric phenomena include electrical, optical and other phenomena such as fogs, blizzards, dust storms, haze, thunderstorm, mirages, squalls, whirlwinds, tornadoes and some others. Let us dwell on the most dangerous of these phenomena.

Storm - it is a complex atmospheric phenomenon, a necessary part of which are multiple electrical discharges between clouds or between a cloud and the earth (lightning), accompanied by sound phenomena - thunder. A thunderstorm is associated with the development of powerful cumulonimbus clouds and therefore is usually accompanied by squally winds and heavy rainfall, often with hail. Most often, thunderstorms and hail are observed in the rear of cyclones during the invasion of cold air, when the most favorable conditions for the development of turbulence are created. Thunderstorms of any intensity and duration are the most dangerous for the flight of aircraft due to the possibility of being hit by their electric discharges. The electrical overvoltage arising at this time spreads through the wires of power transmission lines and switchgears, creates interference and emergency situations. In addition, during thunderstorms, active ionization of the air and the formation of an electric field of the atmosphere occur, which has a physiological effect on living organisms. It is estimated that an average of 3,000 people die from lightning strikes around the world every year.

From an architectural point of view, a thunderstorm is not very dangerous. Buildings are usually protected from lightning by using lightning rods (often called lightning rods), which are electrical discharge grounding devices that are installed at the highest parts of the roof. Rarely do buildings catch fire when struck by lightning.

For engineering structures (radio and telemasters), a thunderstorm is dangerous mainly because a lightning strike can damage the radio equipment installed on them.

Hail Precipitation is called precipitation falling out in the form of dense ice particles of irregular shape of various, sometimes very large sizes. Hail falls, as a rule, in the warm season from powerful cumulonimbus clouds. The mass of large hailstones is several grams, in exceptional cases - several hundred grams. The hail affects mainly green spaces, especially trees, especially during the flowering period. In some cases, hail takes on a character natural Disasters... So, in April 1981 in Guangdong province, China, 7 kg hailstones were observed. As a result, five people died and about 10.5 thousand buildings were destroyed. At the same time, observing with the help of special radar means for the development of hail centers in cumulonimbus clouds and applying methods active impact on these clouds, in about 75% of cases, this dangerous phenomenon can be prevented.

Flurry - a sharp increase in the wind, accompanied by a change in its direction and usually lasting within no more than 30 minutes. Frontal cyclonic activity is usually accompanied by squalls. As a rule, squalls occur during the warm season on active atmospheric fronts, as well as during the passage of powerful cumulonimbus clouds. The wind speed in squalls reaches 25-30 m / s and more. The squall strip is usually about 0.5-1.0 km wide and 20-30 km long. The passage of squalls causes the destruction of buildings, communication lines, damage to trees and other natural disasters.

The most dangerous destruction from the effects of wind occurs during the passage tornado- a powerful vertical vortex generated by an ascending stream of warm moist air. The tornado looks like a dark cloudy column with a diameter of several tens of meters. It descends in the form of a funnel from the low base of a cumulonimbus cloud, towards which another funnel can rise from the earth's surface - from spray and dust, connecting with the first. Wind speeds in a tornado reach 50-100 m / s (180-360 km / h), which causes catastrophic consequences. A blow from a rotating wall of a tornado is capable of destroying capital structures. The pressure drop from the outer wall of the tornado to its inner side leads to explosions of buildings, and the ascending air flow is able to lift and transfer heavy objects, debris of building structures, wheeled and other equipment, people and animals over considerable distances. According to some estimates, in the cities of Russia, such phenomena can be observed approximately once every 200 years, but in other parts of the world they are observed regularly. In the XX century. the most destructive in Moscow was a tornado that took place on June 29, 1909. In addition to the destruction of buildings, nine people died, 233 people were hospitalized.

In the USA, where tornadoes are observed quite often (sometimes several times a year), they are called "tornadoes". They are exceptionally high in frequency compared to European tornadoes and are mainly associated with the tropical marine air of the Gulf of Mexico, moving towards the southern states. The damage and loss caused by these tornadoes is enormous. In areas where tornadoes are most often observed, even a peculiar architectural form of buildings has arisen, called "Tornado house". It is characterized by a squat reinforced concrete shell in the form of a spreading drop, which has door and window openings that are tightly closed with durable roller shutters in case of danger.

Considered above dangerous phenomena mainly observed during the warm season. In the cold season, the most dangerous are the previously mentioned ice and strong blizzard- transfer of snow over the surface of the earth by wind of sufficient force. It usually occurs when increasing gradients in the field atmospheric pressure and when passing the fronts.

Weather stations monitor the duration of snowstorms and the number of days with a snowstorm for individual months and the winter period as a whole. The average annual duration of snowstorms in the territory of the former USSR per year is in the south Central Asia less than 10 hours, on the coast of the Kara Sea - more than 1000 hours. In most of the territory of Russia, the duration of snowstorms is more than 200 hours per winter, and the duration of one snowstorm is on average 6-8 hours.

Blizzards cause great damage to the city economy due to the resulting snow drifts of streets and roads, snow deposition in the wind shadow of buildings on the territory of residential development. In some areas Of the Far East buildings on the leeward side are swept up with such a high layer of snow that after the end of the blizzard it is impossible to get out of them.

Snowstorms complicate the work of air, rail and road transport, utilities. Agriculture also suffers from snowstorms: with strong winds and a loose structure of snow cover, snow is redistributed in the fields, areas are exposed, conditions are created for winter crops to freeze. Blizzards also affect people, creating discomfort when being outdoors. A strong wind in combination with snow disrupts the rhythm of the breathing process, creates difficulties for movement and work. During periods of snowstorms, the so-called meteorological heat loss of buildings and the consumption of energy used for industrial and domestic needs increase.

Bioclimatic and architectural and construction significance of precipitation and phenomena. It is believed that biological action rainfall on the human body is mainly characterized by a beneficial effect. When they fall out of the atmosphere, pollutants and aerosols, dust particles, including those on which pathogenic microbes are transferred, are washed out. Convective showers contribute to the formation of negative ions in the atmosphere. So, in the warm period of the year after a thunderstorm, patients have a decrease in meteopathic complaints, the likelihood of infectious diseases... In the cold period, when precipitation mainly falls in the form of snow, it reflects up to 97% of ultraviolet rays, which is used in some mountain resorts, spending "sunbathing" at this time of the year.

At the same time, it should be noted and negative role precipitation, namely the associated problem acid rain. These sediments contain solutions of sulfuric, nitric, hydrochloric and other acids formed from oxides of sulfur, nitrogen, chlorine, etc., emitted in the course of economic activity. As a result of such precipitation, soil and water pollution occurs. For example, the mobility of aluminum, copper, cadmium, lead and other heavy metals increases, which leads to an increase in their migratory ability and transport over long distances. Acidic precipitation intensifies the corrosion of metals, thereby having a negative effect on roofing materials and metal structures of buildings and structures exposed to precipitation.

In areas with dry or rainy (snowy) climates precipitation are as important a factor in shaping in architecture as solar radiation, wind and temperature conditions. Particular attention is paid to atmospheric precipitation when choosing the construction of walls, roofs and foundations of buildings, the selection of building and roofing materials.

The impact of atmospheric precipitation on buildings consists in moistening the roof and external fences, leading to a change in their mechanical and thermophysical properties and affecting the service life, as well as in the mechanical load on building structures created by solid precipitation accumulating on the roof and protruding elements of buildings. This impact depends on the mode of precipitation and the conditions for the removal or occurrence of atmospheric precipitation. Depending on the type of climate, precipitation can fall evenly throughout the year or mainly in one of its seasons, and this fallout can have the character of showers or drizzling rains, which is also important to take into account in the architectural design of buildings.

The conditions of accumulation on different surfaces are important mainly for solid precipitation and depend on the air temperature and wind speed, which redistributes the snow cover. The highest snow cover in Russia is observed on the eastern coast of Kamchatka, where the average of the highest ten-day heights reaches 100-120 cm, and every 10 years - 1.5 m. In some areas of the southern part of Kamchatka average height The snow cover can exceed 2 m. The height of the snow cover increases with the height of the site above sea level. Even small hills affect the height of the snow cover, but the influence of large mountain ranges is especially great.

To clarify snow loads and determine the mode of operation of buildings and structures, it is necessary to take into account the possible weight of the snow cover formed during the winter and its maximum possible increase during the day. The change in the weight of the snow cover, which can occur in just a day as a result of intense snowfalls, can vary from 19 (Tashkent) to 100 or more (Kamchatka) kg / m 2. In areas with a small and unstable snow cover, one heavy snowfall during the day creates a load close to its value, which is possible every five years. Such snowfalls were observed in Kiev,

Batumi and Vladivostok. This data is especially necessary for the design of lightweight roofs and prefabricated metal frame structures with a large roof surface (for example, awnings over large parking lots, transport hubs).

Falling snow can be actively redistributed over the territory of urban development or in the natural landscape, as well as within the roof of buildings. In some areas it is blown out, in others it is accumulated. The patterns of such a redistribution have complex nature and depend on the direction and speed of the wind and the aerodynamic properties of urban development and individual buildings, natural relief and vegetation cover.

Accounting for the amount of snow carried during blizzards is necessary to protect the adjoining territories, road network, roads and railways from snow drifts. Data on snow drifts are also needed in the planning of settlements for the most rational placement of residential and industrial buildings, in the development of measures for clearing snow from cities.

The main snow protection measures are to choose the most favorable orientation of buildings and the road network (UDS), which ensures the minimum possible accumulation of snow on the streets and at the entrances to buildings and the most favorable conditions for the transit of wind-blown snow through the territory of the UDS and residential development.

The peculiarities of snow deposition around buildings are that the maximum deposits are formed on the leeward and windward sides in front of the buildings. Directly in front of the windward facades of buildings and near their corners, "blowing gutters" are formed (Fig. 1.53). It is advisable to take into account the regularities of the redeposition of the snow cover during the snow drift when placing the entrance groups. Entrance groups to buildings in climatic regions characterized by large volumes of snow transfer should be located on the windward side with appropriate insulation.

For groups of buildings, the process of snow redistribution is more complex. Shown in Fig. 1.54 snow redistribution schemes show that in the microdistrict, traditional for the development of modern cities, where the quarter perimeter is formed by 17-storey buildings, and a three-storey kindergarten building is located inside the quarter, a vast snow accumulation zone forms in the inner districts of the quarter: snow accumulates at the entrances

• 1 - initiating stream; 2 - the upper flowing branch; 3 - compensation vortex; 4 - suction zone; 5 - windward part of the annular vortex (blowing zone); 6 - zone of collision of oncoming streams (windward side of deceleration);
• 7 - the same, on the leeward side

• - transfer
• - blowing

Rice. 1.54. Redistribution of snow within groups of buildings of different storeys

Accumulation

residential buildings and on the territory of the kindergarten. As a result, in such an area it is necessary to carry out snow removal after each snowfall. In another embodiment, the buildings that form the perimeter are much lower than the building located in the center of the block. As can be seen from the figure, the second option is more favorable in terms of the snow accumulation factor. The total area of ​​snow transfer and blowing zones is larger than the area of ​​snow accumulation zones, the space inside the block does not accumulate snow, and maintenance of the residential area in winter becomes much easier. This option is preferable for areas with active snow transport.

For protection against snow drifts, windproof green spaces can be used, formed in the form of multi-row plantings. conifers from the prevailing winds during blizzards and blizzards. The effect of these windbreak strips is observed at a distance of up to 20 tree heights in plantings, therefore, their use is advisable to protect against snow drifts along linear objects (transport highways) or small building sites. In areas where the maximum volume of snow transfer during the winter is more than 600 m 3 / linear m (areas of Vorkuta, Anadyr, the Yamal, Taimyr peninsulas, etc.), protection by forest belts is ineffective, protection by urban planning and planning means is necessary.

Under the influence of the wind, solid precipitation is redistributed over the roofs of buildings. The snow accumulating on them creates loads on the structures. The design should take these loads into account and, if possible, avoid the occurrence of snow accumulation points (snow bags). Part of the precipitation is blown off the roof onto the ground, part is redistributed along the roof depending on its size, shape and the presence of superstructures, lanterns, etc. The standard value of the snow load on the horizontal projection of the pavement in accordance with SP 20.13330.2011 "Loads and Impacts" should be determined by the formula

^ = 0.7C in C, p ^,

where C in is a coefficient that takes into account the drift of snow from the coatings of buildings under the influence of wind or other factors; WITH, - thermal coefficient; p is the coefficient of transition from the weight of the snow cover of the earth to the snow load on the cover; ^ - the weight of the snow cover per 1 m 2 of the horizontal surface of the earth, taken in accordance with the table. 1.22.

Table 1.22

The weight of the snow cover per 1 m 2 of the horizontal surface of the earth

Snowy areas *
Snow cover weight, kg / m 2

* Accepted by card 1 of Appendix "G" to JV "Urban Planning".

The values ​​of the coefficient C in, taking into account the drift of snow from the coatings of buildings under the influence of the wind, depend on the shape and size of the roof and can vary from 1.0 (drift of snow is not taken into account) to several tenths of a unit. For example, for coatings of high-rise buildings with a height of over 75 m with slopes up to 20% C, it is allowed to take in the amount of 0.7. For domed spherical and conical roofs of buildings on a circular plan, when setting a uniformly distributed snow load, the value of the coefficient C in is set depending on the diameter ( with!) the base of the dome: C in = 0.85 at с1 60 m, С в = 1.0 at c1> 100 m, and in intermediate values ​​of the diameter of the dome, this value is calculated using a special formula.

Thermal coefficient WITH, It is used to take into account the decrease in snow loads on coatings with a high heat transfer coefficient (> 1 W / (m 2 C) due to melting caused by heat loss. When determining snow loads for non-insulated coatings of buildings with increased heat emissions, leading to snow melting, with roof slopes above 3% coefficient value WITH, is 0.8, in other cases - 1.0.

The coefficient of transition from the weight of the snow cover of the earth to the snow load on the cover p is directly related to the shape of the roof, since its value is determined depending on the steepness of its slopes. For buildings with shed and gable roofs, the value of the p coefficient is 1.0 with a roof slope of 60 °. Intermediate values ​​are determined by linear interpolation. Thus, when the slope of the pavement is more than 60 °, the snow is not held on it and almost all of it slides down under the influence of gravity. Coverings with such a slope are widely used in the traditional architecture of the northern countries, in mountainous regions and in the construction of buildings and structures that do not provide for sufficiently strong roof structures - domes and tents of towers with a large span and a roof over a wooden frame. In all these cases, it is necessary to provide for the possibility of temporary storage and subsequent removal of snow sliding from the roof.

With the interaction of wind and buildings, there is a redistribution of not only solid, but also liquid precipitation. It consists in increasing their number from the windward side of buildings, in the zone of inhibition of the wind flow and from the side of the windward corners of buildings, where precipitation contained in the additional volumes of air flowing around the building enters. Waterlogging of walls, wetting of interpanel joints, deterioration of the microclimate of windward premises are associated with this phenomenon. For example, the windward facade of a typical 17-storey 3-section residential building with an average rainfall rate of 0.1 mm / min and a wind speed of 5 m / s intercepts about 50 tons of water per hour. Part of it is spent on wetting the facade and protruding elements, the rest flows down the wall, causing unfavorable consequences for the local area.

To protect the facades of residential buildings from getting wet, it is recommended to increase the area open spaces along the windward facade, the use of moisture-proof screens, waterproof cladding, reinforced waterproofing of joints. Around the perimeter, it is necessary to provide drainage trays connected to the systems storm sewer... In their absence, water flowing down the walls of a building can erode the surface of lawns, causing surface erosion of the vegetation layer of the soil and damaging green spaces.

In architectural design, questions arise related to the assessment of the intensity of ice formation on certain parts of buildings. The amount of ice load on them depends on climatic conditions and on technical parameters each object (size, shape, roughness, etc.). The solution of issues related to the prevention of ice formations and related violations of the operation of buildings and structures and even the destruction of their individual parts is one of the most important tasks of architectural climatography.

The effect of ice on various structures is the formation of ice loads. The magnitude of these loads has a decisive influence on the choice of structural parameters of buildings and structures. Ice-rime ice deposits are also harmful for trees and shrubs, which form the basis of urban greening. Branches and sometimes trunks of trees break under their weight. The productivity of orchards is decreasing, the productivity of agriculture is decreasing. The formation of ice and ice on the roads creates dangerous conditions for the movement of ground transport.

Icicles (a particular case of ice phenomena) pose a great danger to buildings and people and objects nearby (for example, parked cars, benches, etc.). To reduce the formation of icicles and ice on the eaves of the roofs, the project should provide for special measures. Passive measures include: reinforced thermal insulation of the roof and attic floors, the air gap between the roof covering and its structural base, the possibility of natural ventilation of the sub-roof space with cold outside air. In some cases, it is impossible to do without active engineering measures, such as electric heating of the eaves removal, installation of shockers for dropping ice in small doses as they form, etc.

Architecture is greatly influenced by the combined effect of wind, sand and dust - dust storms which also refer to atmospheric phenomena. The combination of wind and dust requires the protection of the living environment. The level of non-toxic dust content in a dwelling should not exceed 0.15 mg / m 3, and the maximum permissible concentration (MPC) for calculations is taken to be no more than 0.5 mg / m 3. The intensity of the transfer of sand and dust, as well as snow, depends on the wind speed, local features of the relief, the presence of non-turfed areas of the relief on the windward side, the granulometric composition of the soil, its moisture content and other conditions. The patterns of sand and dust deposition around buildings and in the development area are approximately the same as those of snow. The maximum deposits form on the leeward and windward sides of the building or their roofs.

The methods of dealing with this phenomenon are the same as for snow transport. In areas with high air dustiness (Kalmykia, Astrakhan region, Caspian part of Kazakhstan, etc.) it is recommended: a special layout of dwellings with the orientation of the main premises to the protected side or with a dustproof glazed corridor; appropriate layout of the quarters; optimal direction of streets, forest shelter belts, etc.

Water molecules are constantly evaporating from the surface of lakes, seas, rivers and oceans - they enter the atmosphere, where they are converted into water vapor, and then into various types of precipitation... There is always water vapor in the air, which is usually impossible to see, but the humidity of the air depends on its amount.

Air humidity is different in all regions of the world, in heat it rises when evaporation into the atmosphere from the surface of water bodies increases. Low humidity is usually observed over desert areas, as there is little water vapor, so the air in deserts is very dry.

Water vapor overcomes many challenges before falling to the ground in the form of rain, snow or frost.

The surface of the earth is heated by the sun's rays, and the resulting heat is transferred to the air. Since heated air masses much easier than cold ones, they rise. Tiny water droplets that formed in the air continue to travel further with it in type of precipitation.

Types of precipitation, fog and clouds.

To imagine how the further transformation of water vapor in the atmosphere takes place, a fairly simple experiment can be carried out. It is necessary to take a mirror and bring it closer to the spout of a boiling kettle. After a few seconds, the cool surface of the mirror will fog up, then large water droplets will form on it. The released steam turned into water, which means that a phenomenon called condensation has occurred.

A similar phenomenon occurs with water vapor at a distance of 2-3 km from the ground. Since the air at this distance is colder than near the surface of the earth, vapor condensation occurs in it and water droplets are formed, which can be observed from the ground in the form of clouds.

When flying in an airplane, clouds can sometimes be seen below the aircraft. And you can even find yourself among the clouds if you climb a high mountain with low clouds. At this moment, the surrounding objects and people will turn into invisible people, who are swallowed up by a thick veil of fog. Fog is the same clouds, but only located near the earth's surface.

If the drops in the clouds begin to grow and become heavier, then the snow-white clouds gradually darken and turn into clouds. When heavy droplets are no longer able to stay in the air, then rain falls from thunderclouds onto the ground in type of precipitation.

Dew and frost as types of precipitation.

In summer, near water bodies, a lot of steam is formed in the air and it becomes very saturated with water pores. With the onset of night, coolness comes and at this time less steam is required to saturate the air. Excess moisture condenses on the ground, leaves, grass and other objects, and such type of precipitation called dew. Dew can be observed in the early morning when transparent small droplets can be seen covering various objects.

With the arrival of late autumn, the temperature during the night can drop below 0 ° C, then the dew drops freeze and turn into amazing transparent crystals called frost.

In winter, ice crystals freeze and settle on window panes in the form of frosty patterns of extraordinary beauty. Sometimes frost simply covers the surface of the earth, like a thin layer of snow. Fancy patterns are best seen on rough surfaces such as:

• tree branches;
• loose surface of the earth;
• wooden benches.

Snow and hail as types of precipitation.

Hail are irregularly shaped pieces of ice that fall to the ground with rain in summer. There is also "dry" hail, it falls without rain. If you carefully cut the hailstone, you can see on the cut that it consists of alternating opaque and transparent layers.

When air currents bring water vapor to a height of about 5 km, then water droplets begin to settle on the dust particles, and they instantly freeze. The formed ice crystals begin to increase in size, and having reached heavy weight start to fall. But a new stream of warm air emanates from the earth and it returns them back to the cold cloud. The gravels begin to grow again and try to fall, this process is repeated several times, as soon as they have gained enough heavy weight, they fall to the ground.

The size of such types of precipitation(grains) is usually 1 to 5 mm in diameter. Although there were cases when the size of the hailstones exceeded egg, and the weight reached about 400-800 g.

Very heavy damage hail can inflict agriculture, it damages vegetable gardens and crops, and also leads to the death of small animals. Large hailstones can damage cars and even pierce the skin of aircraft.

To reduce the likelihood of hail falling on the ground, scientists are constantly developing new substances that, using special rockets, are thrown into thunderclouds and thus disperse them.

With the arrival of winter, a snow-white blanket envelops the earth, consisting of the smallest ice crystals called snow. Because of low temperatures water droplets freeze and ice crystals form in the clouds, then new water molecules are attached to them, and as a result, a separate snowflake is born. All snowflakes have six corners, but the patterns woven on them by frost are different from each other. If the wind blows on the snowflakes, they stick together and form snowflakes. Walking through the snow in frosty weather, we often hear a crunch under our feet, it is ice crystals breaking in snowflakes.

Such types of precipitation How snow brings a lot of problems, snow makes it difficult to move on the roads, power lines are torn under its weight, and melting snows leads to floods. But due to the fact that the plants are covered with a snow blanket, they are able to withstand even severe frosts.

Precipitation- water in a liquid or solid state, falling out of clouds or deposited from the air on the earth's surface.

Rain

Under certain conditions, cloudy drops begin to merge into larger and heavier ones. They can no longer be held in the atmosphere and fall to the ground in the form rain.

Hail

It happens that in summer the air rises quickly, picks up rain clouds and carries them to a height where the temperature is below 0 °. Raindrops freeze and fall out as hail(fig. 1).

Rice. 1. Origin of the city

Snow

In winter, in temperate and high latitudes, precipitation falls in the form snow. Clouds at this time do not consist of water droplets, but of the smallest crystals - needles, which, joining together, form snowflakes.

Dew and frost

Precipitation falling on the earth's surface not only from clouds, but also directly from the air is dew and frost.

The amount of precipitation is measured by a rain gauge or a rain gauge (Fig. 2).

Rice. 2. The structure of the rain gauge: 1 - outer case; 2 - funnel; 3 - container for collecting oxen; 4 - dimensional tank

Classification and types of precipitation

Precipitation is distinguished by the nature of precipitation, origin, physical condition, seasons of precipitation, etc. (Fig. 3).

By the nature of precipitation, precipitation is heavy, heavy and drizzling. Heavy rainfall - intense, short, cover a small area. Overhead precipitation - medium intensity, uniform, long-term (can last for days, capturing large areas). Drizzling precipitation - fine-droplet precipitation falling on an insignificant area.

Precipitation is distinguished by origin:

• convective - characteristic of the hot zone, where heating and evaporation are intense, but often occur in the temperate zone;
• frontal - are formed when two air masses with different temperatures meet and fall out of warmer air. Typical for temperate and cold zones;
• orographic - fall on the windward slopes of the mountains. They are very abundant if the air comes from the warm sea and has a high absolute and relative humidity.

Rice. 3. Types of precipitation

Comparing on climate map the annual amount of atmospheric precipitation in the Amazonian lowland and in the Sahara desert, one can be convinced of their uneven distribution (Fig. 4). How can this be explained?

Precipitation brings moist air masses that form over the ocean. This is clearly illustrated by the example of territories with a monsoon climate. The summer monsoon brings a lot of moisture from the ocean. And there are continuous rains over land, like on the Pacific coast of Eurasia.

Constant winds also play a large role in the distribution of precipitation. Thus, trade winds blowing from the continent bring dry air to northern Africa, where the most vast desert the world - the Sahara. Westerly winds bring rains to Europe from the Atlantic Ocean.

Rice. 4. Average annual distribution of precipitation on the Earth's land

As you already know, sea currents affect precipitation in the coastal parts of the continents: warm currents contribute to their appearance (the Mozambican current off the eastern coast of Africa, the Gulf Stream off the coast of Europe), cold ones, on the contrary, prevent precipitation ( Peruvian current off the western coast of South America).

The relief also affects the distribution of precipitation, for example, the Himalayan mountains do not allow wet winds blowing from Indian Ocean... Therefore, their southern slopes sometimes receive up to 20,000 mm of precipitation per year. Wet air masses, rising along the slopes of mountains (ascending currents of air), are cooled, saturated, and precipitation falls out of them. The territory north of the Himalayan mountains resembles a desert: only 200 mm of precipitation falls there per year.

There is a relationship between the belts and the amount of precipitation. At the equator - in the belt low pressure- constantly heated air; rising up, it cools and saturates. Therefore, many clouds form in the equator area and there are heavy rains. A lot of precipitation also falls in other regions of the world, where low pressure prevails. Wherein great importance has an air temperature: the lower it is, the less precipitation falls.

Downward air currents prevail in high pressure belts. As the air sinks, it heats up and loses its saturation state. Therefore, at latitudes of 25-30 °, precipitation is rare and in small quantities. There is also little rainfall in high pressure areas near the poles.

Absolute maximum precipitation registered on about. Hawaii (Pacific Ocean) - 11,684 mm / year and Cherrapunji (India) - 11,600 mm / year. The absolute minimum is in the Atacama Desert and in the Libyan Desert - less than 50 mm / year; sometimes precipitation does not fall for years at all.

The characteristic of the moistening of the territory is moisture factor- the ratio of annual precipitation and evaporation for the same period. The moisture coefficient is designated by the letter K, the annual precipitation is by the letter O, and the evaporation is by I; then K = O: I.

The lower the moisture coefficient, the drier the climate. If the annual amount of precipitation is approximately equal to the evaporation rate, then the moisture coefficient is close to unity. In this case, moisture is considered sufficient. If the moisture index is more than one, then the moisture excess, less than one - insufficient. With a humidification coefficient less than 0.3, humidification is considered meager... Areas with sufficient moisture include forest-steppe and steppe, areas with insufficient moisture - deserts.

First of all, let us define the very concept of "precipitation". In the "Meteorological Dictionary, this term is interpreted as follows:" Precipitation is water in a liquid or solid state, falling out of clouds or deposited from the air on the surface of the earth and on objects. "

According to the above definition, atmospheric precipitation can be divided into two groups: precipitation emitted directly from the air - dew, hoarfrost, rime, ice, and precipitation falling from clouds - rain, drizzle, snow, snow pellets, hail.

Each type of precipitation has its own characteristics.

Dew represents the smallest droplets of water deposited on the surface of the earth and on ground objects (grass, tree leaves, roofs, etc.). Dew forms at night or in the evening in clear, calm weather.

Frost appears on surfaces cooled below 0 ° C. It is a thin layer crystal ice whose particles are shaped like snowflakes.

Rime- This is the deposition of ice on thin and long objects (tree branches, wires), which forms at any time of the day, usually in cloudy, foggy weather at negative temperatures (below -15 ° C). Rime can be crystalline and granular. On vertical objects, frost is deposited mainly from the windward side.

Among the sediments that stand out on the earth's surface, of particular importance is ice... It is a layer of dense transparent or cloudy ice that grows on any objects (including trunks and branches of trees, bushes) and on the surface of the earth. Formed at an air temperature of 0 to -3 ° C due to freezing drops of supercooled rain, drizzle or fog. The frozen ice crust can be several centimeters thick and cause branching to break off.

Precipitation falling out of clouds is subdivided into drizzling, overlying and showers.

Drizzle (drizzle) consist of very small water droplets with a diameter of less than 0.5 mm. They are of low intensity. These precipitations usually fall from stratus and stratocumulus clouds. The droplets are falling so slowly that they appear suspended in the air.

Overhead precipitation- it is rain, consisting of small water droplets, or snowfall of snowflakes with a diameter of 1-2 mm. This is long-term precipitation falling from dense high-stratus and nimbostratus clouds. They can last for several hours or even days, capturing vast territories.

Heavy rainfall it is distinguished by great intensity. These are coarse droplets and irregular precipitation, both liquid and solid (snow, groats, hail, sleet). The downpour can last from several minutes to several hours. The area covered by a rainstorm is usually small.

Hail, which is always observed during a thunderstorm, usually together with heavy rain, forms in cumulonimbus (thunderstorm) clouds of vertical development. It usually falls in a narrow strip in spring and summer, and most often between 12 and 17 hours. The duration of the hail is calculated in minutes. Within 5-10 minutes, the ground can be covered with a layer of hail several centimeters thick. With intense hail, plants can be damaged in varying degrees or even destroyed.

Precipitation is measured by the thickness of the water layer in millimeters. If 10 mm of precipitation fell, then this means that the layer of water that fell on the surface of the earth is 10 mm. And what does 10 mm of precipitation mean for a plot of 600 m2? It’s not hard to calculate. Let's start the calculation for an area equal to 1 m 2. For her, this amount of precipitation will be 10,000 cm 3, ie 10 liters of water. And this is a whole bucket. This means that for an area equal to 100 m 2, the amount of precipitation will already be equal to 100 buckets, but for an area of ​​six acres - 600 buckets, or six tons of water. This is what 10 mm of rainfall is for a typical garden plot.

Precipitation and their classification.

Precipitation classification. By type, atmospheric precipitation is divided into liquid, solid and ground.

TO liquid precipitation relate:

rain - precipitation in the form of drops of various sizes with a diameter of 0.5–7 mm;

drizzle - small droplets with a diameter of 0.05–0.5 mm, which are, as it were, in suspension.

Solid sediments include:

snow - ice crystals forming various kinds of snowflakes (plates, needles, stars, columns) 4–5 mm in size. Sometimes snowflakes are combined into snow flakes, the size of which can reach 5 cm or more;

snow groats - precipitation in the form of opaque spherical grains of white or dull white (milky) color with a diameter of 2 to 5 mm;

ice croup - solid particles, transparent from the surface, having an opaque matte core in the center. The diameter of the grains is from 2 to 5 mm;

hail - more or less large pieces of ice (hailstones) with spherical or irregular shape and complex internal structure... The diameter of the hailstones varies within a very wide range: from 5 mm to 5–8 cm. There are cases when hailstones weighing 500 g or more have been reported.

If precipitation does not fall out of clouds, but is deposited from the atmospheric air on the earth's surface or on objects, then such precipitation is called ground. These include:

dew - the smallest drops of water condensing on the horizontal surfaces of objects (deck, boat tents, etc.) due to their radiation cooling on clear cloudless nights. Little wind(0.5–10 m / s) promotes dew formation. If the temperature of horizontal surfaces is below zero, then water vapor in similar conditions sublimates on them and frost forms - a thin layer of ice crystals;

liquid plaque - the smallest drops of water or a continuous film of water that form in cloudy and windy weather on the windward, predominantly vertical surfaces of cold objects (walls of superstructures, protective devices for winches, cranes, etc.).

ice is an ice crust formed when the temperature of the indicated surfaces is below 0 ° C. In addition, hard deposits can form on the surfaces of the vessel - a layer of crystals densely or densely sitting on the surface or a thin continuous layer of smooth transparent ice.

In foggy frosty weather, with a weak wind, granular or crystalline frost may form on the vessel's rigging, ledges, cornices, wires, etc. Unlike frost, frost does not form on horizontal surfaces. The loose structure of rime distinguishes it from hard bloom. Granular rime is formed at an air temperature of –2 to –7 ° C due to freezing on the subject of supercooled fog droplets, and crystalline rime, which is a white precipitate of fine crystals of crystals, forms at night with a cloudless sky or thin clouds of fog or haze particles at a temperature from –11 to –2 ° С and higher.

According to the nature of the fallout, atmospheric precipitation is divided into torrential, overlying and drizzling.

Heavy rain falls from cumulonimbus (thunderstorm) clouds. In summer it is coarse rain (sometimes with hail), and in winter it is heavy snowfall with frequent changes in the shape of snowflakes, snow or ice grains. Overburden precipitation falls from nimbostratus (summer) and altostratus (winter) clouds. They are characterized by small fluctuations in intensity and long shedding duration.