Atmospheric precipitation. Types of precipitation: (according to the nature of precipitation) What precipitation is and its types

Atmospheric precipitation is the name given to water that falls from the atmosphere onto the earth's surface. Atmospheric precipitation also has a more scientific name - hydrometeors.

They are measured in millimeters. To do this, measure the thickness of water that has fallen to the surface using special instruments - precipitation gauges. If you need to measure the water thickness over large areas, then weather radars are used.

On average, our Earth receives almost 1000 mm of precipitation annually. But it is quite predictable that the amount of moisture that falls depends on many conditions: climate and weather conditions, terrain and proximity to water bodies.

Types of precipitation

Water from the atmosphere falls onto the earth's surface, being in its two states - liquid and solid. According to this principle, everything precipitation It is customary to divide them into liquid (rain and dew) and solid (hail, frost and snow). Let's look at each of these types in more detail.

Liquid precipitation

Liquid precipitation falls to the ground in the form of water droplets.

Rain

Evaporating from the surface of the earth, water in the atmosphere collects in clouds, which consist of tiny droplets ranging in size from 0.05 to 0.1 mm. These miniature droplets in the clouds merge with each other over time, becoming larger in size and noticeably heavier. Visually, this process can be observed when the snow-white cloud begins to darken and become heavier. When there are too many such drops in a cloud, they fall to the ground in the form of rain.

In summer it's raining in the form of large drops. They remain large because heated air rises from the ground. These rising jets prevent the drops from breaking into smaller ones.

But in spring and autumn the air is much cooler, so during these times of year the rain is drizzling. Moreover, if the rain comes from stratus clouds, it is called cover clouds, and if drops begin to fall from nimbus clouds, then the rain turns into downpour.

Every year, almost 1 billion tons of water fall on our planet in the form of rain.

It is worth highlighting in a separate category drizzle. This type of precipitation also falls from stratus clouds, but the droplets are so small and their speed is so negligible that the water droplets appear suspended in the air.

Dew

Another type of liquid precipitation that falls at night or early in the morning. Dew droplets are formed from water vapor. Overnight, this steam cools, and the water turns from a gaseous state into a liquid.

The most favorable conditions for dew formation: clear weather, warm air and almost complete absence wind.

Solid precipitation

We can observe solid precipitation in the cold season, when the air cools to such an extent that water droplets in the air freeze.

Snow

Snow, like rain, forms in a cloud. Then, when the cloud enters a stream of air in which the temperature is below 0°C, the water droplets in it freeze, become heavy and fall to the ground as snow. Each droplet solidifies into a kind of crystal. Scientists say that all snowflakes have different shapes and it is simply impossible to find identical ones.

By the way, snowflakes fall very slowly, since they are almost 95% air. For the same reason they white. And the snow crunches underfoot because the crystals are breaking. And our hearing is able to catch this sound. But for the fish it’s a real torment, since snowflakes falling on the water emit a high-frequency sound that the fish hear.

hail

falls only in the warm season, especially if the day before it was very hot and stuffy. The heated air rushes upward in strong currents, carrying with it the evaporated water. Heavy cumulus clouds. Then, under the influence of rising currents, the water droplets in them become heavier, begin to freeze and become overgrown with crystals. These lumps of crystals rush to the ground, increasing in size along the way due to merging with drops of supercooled water in the atmosphere.

It must be taken into account that such icy “snowballs” rush to the ground with incredible speed, and therefore hail is capable of breaking through slate or glass. Hail causes great damage to agriculture, so the most “dangerous” clouds that are ready to burst into hail are dispersed with the help of special guns.

Frost

Frost, like dew, is formed from water vapor. But in the winter and autumn months, when it is already quite cold, the water droplets freeze and therefore fall out in the form of a thin layer of ice crystals. But they don’t melt because the earth is cooling even more.

Rainy seasons

In the tropics and very rarely in temperate latitudes, there comes a time of year when an inordinate amount of precipitation falls. This period is called the rainy season.

In countries located in these latitudes, there are no severe winters. But spring, summer and autumn are incredibly hot. During this hot period, a huge amount of moisture accumulates in the atmosphere, which then pours out in the form of prolonged rains.

In the equator region, the rainy season occurs twice a year. And in the tropical zone, south and north of the equator, such a season occurs only once a year. This is due to the fact that the rain belt gradually runs from south to north and back.

The evaporation of water vapor, its transport and condensation in the atmosphere, the formation of clouds and precipitation constitute a single complex climate-forming moisture circulation process, as a result of which there is a continuous transition of water from the earth's surface into the air and from the air again to the earth's surface. Precipitation is a critical component of this process; It is they, along with air temperature, that play a decisive role among those phenomena that are united under the concept of “weather.”

Atmospheric precipitation is called 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 layer of water in mm formed on a horizontal surface from rain, 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 from clouds - rain, snow, hail, pellets, 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 - cloudiness, 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 lighting conditions. At the same time, they increase scattered radiation and reduce effective radiation, which increases absorbed radiation.

By changing the radiation and thermal regime of the atmosphere, clouds have a great influence on the flora and fauna, 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 coming to the building territory, to buildings and structures and determining their thermal balance and natural light conditions internal environment. Secondly, the phenomenon of cloudiness is associated with precipitation, which determines the humidity regime of operation of buildings and structures, affecting the thermal conductivity of enclosing structures, their durability, etc. Thirdly, the fall of solid precipitation from clouds determines the snow load on buildings, and hence the shape and design of the roof and other architectural and typological features associated with snow cover. Thus, before moving on to consideration of precipitation, it is necessary to dwell in more detail on the phenomenon of cloudiness.

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

The forms of clouds in the troposphere are very diverse, but they can be reduced to a relatively small number of basic types. This “morphological” classification of clouds (that is, classification according to their appearance) arose in the 19th century. and is generally accepted. According to it, all clouds are divided into 10 main genera.

In the troposphere, three layers of clouds are conventionally distinguished: upper, middle and lower. Cloud bases upper tier 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 to 2 km. Upper level clouds include feathery, cirrocumulus And pinnately stratified. They consist of ice crystals, are translucent and offer little shading. sunlight. In the middle tier there are altocumulus(drip) and highly stratified(mixed) clouds. In the lower tier there are layered, stratostratus And stratocumulus clouds. Nimbostratus clouds are composed of a mixture of droplets and crystals, the rest are drip clouds. 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 - these are cumulus(drip) and cumulonimbus(mixed) clouds called clouds of vertical development.

The degree of cloud coverage of the sky is called cloudiness. 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 general cloudiness, but also lower cloudiness, which includes clouds of vertical development, is determined. Thus, cloudiness is written as a fraction, the numerator of which is the total cloudiness, and the denominator is the lower one.

Along with this, cloudiness is determined using photographs obtained from artificial Earth satellites. 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. A comparison of ground-based and satellite data demonstrates good agreement, with the largest differences observed over the continents and amounting to approximately 1 point. Here, ground-based measurements, due to subjective reasons, slightly overestimate the amount of clouds compared to satellite data.

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

In Fig. 1.47 shown total score cloudiness on average for the year for the territory of Russia. As can be seen from this figure, the amount of clouds in Russia is distributed rather unevenly. The most cloudy areas are the north-west of the European part of Russia, where the amount of total cloudiness 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 lower average annual cloud amounts. Here it ranges from 5 to 6 points, and in the far south in some places it is even less than 5 points. This entire relatively cloudy region of the Asian part of Russia is in the sphere of influence of the Asian anticyclone, and therefore is characterized by a low frequency of cyclones, which are mainly associated with a large number of clouds. There is also a strip of less significant clouds, stretched in the meridional direction directly beyond the Urals, which is explained by the “shading” role of these mountains.

Rice. 1.47.

Under certain conditions, they fall out of clouds precipitation. This occurs 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 droplets and ice crystals in the cloud. These are the altostratus, nimbostratus and cumulonimbus clouds from which precipitation falls.

All precipitation is divided into liquid and solid. Liquid precipitation - These are rain and drizzle, they differ in the size of the drops. TO solid sediments include snow, sleet, pellets and hail. The amount of precipitation is measured in mm of the layer of fallen water. 1 mm of precipitation corresponds to 1 kg of water falling over an area of ​​1 m2, provided that it does not drain, evaporate or be absorbed by the soil.

Based on the nature of precipitation, precipitation is divided into the following types: cover precipitation - uniform, long-lasting, falling from nimbostratus clouds; rainfall - characterized by rapid changes in intensity and short duration, they fall from cumulonimbus clouds in the form of rain, often with hail; drizzling precipitation - fall as drizzle from nimbostratus clouds.

Daily variation of precipitation is very complex, and even in long-term average values ​​it is often impossible to detect any pattern in it. Nevertheless, two types of daily precipitation patterns are distinguished: continental And nautical(shore). The continental type has two maximums (in the morning and afternoon) and two minimums (at night and before noon). Marine type characterized by one maximum (at night) and one minimum (day).

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

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

The maximum annual precipitation was recorded in Cherrapunji (India) - 26,461 mm. The minimum recorded annual precipitation is in Aswan (Egypt), Iquique (Chile), where in some years there is no precipitation at all.

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

Measurement methods. The following instruments are used to collect and measure precipitation: Tretyakov precipitation gauge, total precipitation gauge and pluviograph.

Tretyakov precipitation gauge serves to collect and subsequently measure the amount of liquid and solid precipitation that has fallen over a certain period of time. It consists of a cylindrical vessel with a receiving area of ​​200 cm 2, a slatted 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, partitioned with a diaphragm 2 in the form of a truncated cone, into which in summer a funnel with a small hole in the center is inserted to reduce the evaporation of precipitation. The container has a spout to drain liquid. 3, capable 4, soldered on a chain 5 to the vessel. Vessel mounted on tagan 6, surrounded by a cone-shaped protection strip 7, consisting of 16 plates curved according to a special pattern. This protection is necessary to prevent snow from blowing out of the rain gauge in winter and rain drops from strong winds in summer.

The amount of precipitation that fell during the night and day half of the day is measured at the times closest to 8 and 20 hours of standard maternity (winter) time. At 03:00 and 15:00 UTC (universal time coordinated - UTC) in time zones I and II, the main stations also measure precipitation using an additional precipitation gauge, which must be installed at the weather site. For example, at the Moscow State University meteorological observatory, precipitation is measured at 6, 9, 18 and 21 hours standard time. To do this, the measuring bucket, having previously closed the 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 wetting of the sediment collection vessel is added, amounting to 0.1 mm if the water level in the measuring glass is below half the first division, and 0.2 mm if the water level in the measuring glass is at the middle of the first division or higher.

Solid sediments collected in a sediment collection vessel must melt before measurement. To do this, the vessel with sediment is left in a warm room for some time. In this case, the vessel must be closed with a lid and the spout with a cap to avoid evaporation of precipitation and the deposition of moisture on the cold walls on the inside of the vessel. After the solid precipitation has melted, it is poured into a precipitation glass for measurement.

In unpopulated, hard-to-reach areas it is used total precipitation gauge M-70, designed for collecting and subsequently measuring precipitation that has fallen over a long period of time (up to a year). This precipitation gauge consists of a receiving vessel 1 , reservoir (sediment collector) 2, grounds 3 and protection 4 (Fig. 1.49).

The receiving area of ​​the precipitation gauge is 500 cm 2 . The reservoir consists of two detachable parts shaped like cones. To connect the parts of the tank more tightly, a rubber gasket is inserted between them. The receiving vessel is fixed in the opening of the tank

Rice. 1.49.

on the flange. The reservoir with the receiving vessel is mounted on a special base, which consists of three posts connected by spacers. The protection (against wind blowing of precipitation) consists of six plates, which are attached 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 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, preventing their evaporation.

Liquid sediments are selected using a rubber bulb with a tip, solid sediments are carefully broken up and selected with a clean metal mesh or spatula. The amount of liquid precipitation is determined using a measuring cup, and solid precipitation - using scales.

For automatic recording of the quantity 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 sediment receiver 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. Sediment through drain pipes 3 And 4 fall into a recording device consisting of a float chamber 5, inside of which there is a moving float 6. An arrow 7 with a feather is attached to the float rod. Precipitation is recorded on a tape placed on the clock mechanism drum. 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 the control vessel 10. A metal sleeve is mounted on the siphon 11 with clamping coupling 12.

When sediment drains from the receiver into the float chamber, the water level in it rises. In this case, 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 the 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 the zero mark; in the absence of precipitation, the pen draws a horizontal line.

Characteristic values ​​of precipitation amounts. To characterize the climate, average amounts or precipitation amounts for certain periods of time - month, year, etc. It should be noted that the formation of precipitation and its 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, analysis of climate maps allows us to identify the most important patterns of precipitation fields.

In Fig. 1.51 shows 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 50-65° N latitude band. It is here that cyclonic processes actively develop 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, and south of 50° N. latitude. this decrease occurs from northwest to southeast. So, if on the Oka-Don Plain the precipitation is 520-580 mm/year, then in the lower reaches of the river. In the Volga, this amount decreases 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 peaks. At some distance beyond the ridge, on the contrary, there is a decrease in annual precipitation.

Similar to the latitudinal distribution of precipitation on the Russian Plain in the territory Western Siberia in the band 60-65° N. There is a zone of increased precipitation, but it is narrower than in the European part, and there is less precipitation here. For example, in the middle reaches of the river. Ob's 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, compared to the Russian Plain, the area of ​​low precipitation here is significantly shifted to the north.

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

Rice. 1.51.

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

The impact of precipitation on various aspects of human economic activity is expressed not only in more or less strong moistening 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 annual rainfall averages 600 mm, with this amount falling over the three winter months. The same amount of precipitation, but distributed evenly throughout the year, determines the existence of a zone of mixed forests of temperate latitudes. Many hydrological processes are also associated with the patterns of intra-annual precipitation distribution.

From this point of view, an indicative characteristic is the ratio of the amount of precipitation in the cold period to the amount of precipitation in the warm period. 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 observed in Transbaikalia (0.1), where in winter the influence of the Asian anticyclone is most pronounced. On Sakhalin and 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 Caucasus mountain ranges. The predominance of precipitation in the cold period over precipitation in the warm period is observed in Russia only in Black Sea coast Caucasus: for example, in Sochi it is 1.02.

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

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

• an increase in precipitation on the plain in front of the hill ("dammed" precipitation);
• increased precipitation at the highest elevations;
• decrease in precipitation on the leeward side of the hill (“rain shadow”).

The first two types of precipitation are called orographic (Fig. 1.52), i.e. directly related to the influence of 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 air moisture content, which occurred in the first two situations. The quantitative decrease in precipitation in the “rain shadow” is commensurate with its increase at higher elevations; the amount of precipitation in the “damming” is 1.5-2 times higher than the amount of precipitation in the “rain shadow”.

"damming"

Windward

Rainy

Rice. 1.52. Orographic precipitation scheme

Influence of large cities the distribution of precipitation is manifested due to the presence of the “heat island” effect, increased roughness of the urban area and air pollution. Studies conducted in different physical-geographical zones have shown that within the city and in the suburbs located on the windward side, the amount of precipitation increases, with the maximum effect being 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 in all its characteristics, from duration to the occurrence of extreme values. For example, average duration precipitation (hours/month) in the city center (Balchug) exceeds the duration of precipitation in the territory of TSKhA both for the year as a whole 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 of the time on the windward side of the city. For the purposes of architectural and urban planning analysis, the mesoscale precipitation anomaly that forms over the city territory is considered as a background for identifying smaller-scale patterns, which consist mainly in the redistribution of precipitation within the building.

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

Rosa - droplets of water formed on the surface of the earth, on plants and objects as a result of contact of moist air with a colder surface at an air temperature above 0 ° C, a clear sky and calm or light wind. As a rule, dew forms at night, but it can also appear at other times of the day. In some cases, dew can be observed during 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 the built environment where water vapor can condense.

Frost- a white precipitate of a crystalline structure that appears on the surface of the earth and on objects (mainly on horizontal or slightly inclined surfaces). Frost appears when the surface of the earth and objects cool due to the radiation of heat, resulting in a decrease in their temperature to negative values. Frost forms when the air temperature is below zero, when there is calm or light wind and slight cloudiness. Abundant deposition of frost is observed on grass, the surface of leaves of bushes and trees, roofs of buildings and other objects that do not have internal sources heat. Frost can also form on the surface of the wires, causing them to become heavier and increase tension: the thinner the wire, the less frost settles on it. On wires 5 mm thick, frost deposits do 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.

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

Grainy frost is formed due to the freezing of supercooled fog droplets on objects. Its growth is facilitated by high wind speeds and mild frost (from -2 to -7°C, but it also happens at lower temperatures). Granular frost has an amorphous (not crystalline) structure. Sometimes its surface is bumpy and even needle-like, but the needles are usually matte, rough, without crystalline edges. Drops of fog upon contact with a supercooled object freeze so quickly that they do not have time to lose their shape and form a snow-like deposit consisting of ice grains that are not visible to the eye (ice deposit). As the air temperature rises and fog droplets enlarge to the size of drizzle, the density of the resulting granular frost increases, and it gradually turns into ice As the frost intensifies and the wind weakens, the density of the resulting 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 forms.

Crystalline frost - a white precipitate consisting of small ice crystals of a fine structure. When settling on tree branches, wires, cables, etc. Crystalline frost looks like fluffy garlands that easily crumble when shaken. Crystalline frost forms 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 the direct transition into ice (sublimation) of water vapor contained in the air. It is practically harmless for the architectural environment.

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 on the windward side of objects. Along with the concept of “ice”, there is a closely related concept of “black ice”. The difference between them is in the processes that lead to the formation of ice.

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

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

In the life of cities, the condition of roads is also very important, which during 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, and facade decor. It contributes to the freezing, thinning and death of plants present in the urban greening system, and the degradation of natural complexes that make up the urban area due to a lack of oxygen and excess carbon dioxide under the ice shell.

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

Storm - This is a complex atmospheric phenomenon, a necessary part of which is multiple electrical discharges between clouds or between a cloud and the ground (lightning), accompanied by sound phenomena - thunder. A thunderstorm is associated with the development of powerful cumulonimbus clouds and is therefore 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. A thunderstorm of any intensity and duration is the most dangerous for aircraft flights due to the possibility of damaging them with electrical discharges. The electrical overvoltage that occurs at this time spreads along the wires of power communication lines and distribution devices, creating interference and emergency situations. In addition, during thunderstorms, active ionization of the air and the formation of an electric field in 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 each year.

From an architectural point of view, a thunderstorm is not very dangerous. Buildings are usually protected from the effects of lightning by installing lightning rods (often called lightning rods), which are electrical grounding devices installed on the highest areas of the roof. There are rarely cases of buildings catching fire when they are struck by lightning.

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

Hail called precipitation that falls in the form of particles of dense ice irregular shape various, sometimes very large sizes. Hail usually falls in the warm season from powerful cumulonimbus clouds. The mass of large hailstones is several grams, in exceptional cases - several hundred grams. Hail mainly affects green spaces, primarily trees, especially during the flowering period. In some cases, hailstorms become natural disasters. Thus, in April 1981, hailstones weighing 7 kg were observed in Guangdong Province, China. As a result, five people died and about 10.5 thousand buildings were destroyed. At the same time, by monitoring the development of hail foci in cumulonimbus clouds using special radar equipment and using methods of actively influencing these clouds, this dangerous phenomenon can be prevented in approximately 75% of cases.

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

The most dangerous damage caused by wind occurs during the passage of tornado- a powerful vertical vortex generated by an ascending stream of warm, moist air. The tornado looks like a dark cloud 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 splashes and dust, connecting with the first. Wind speeds in a tornado reach 50-100 m/s (180-360 km/h), which causes catastrophic consequences. The impact of the rotating wall of a tornado can destroy permanent structures. The pressure difference from the outer wall of a tornado to its inner side leads to explosions of buildings, and the upward flow of air is capable of lifting and transporting heavy objects, fragments of building structures, wheeled and other equipment, people and animals over considerable distances. According to some estimates, in Russian cities such phenomena can be observed approximately once every 200 years, but in other areas of the globe they are observed regularly. In the 20th century The most destructive tornado in Moscow was on June 29, 1909. In addition to the destruction of buildings, nine people died and 233 people were hospitalized.

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

The dangerous phenomena discussed above are mainly observed during the warm period of the year. 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 strength. It usually occurs with increasing gradients in the atmospheric pressure field and with the passage of fronts.

Weather stations monitor the duration of snowstorms and the number of days with snowstorms over a period of time. individual months And winter period generally. Average annual duration of blizzards in the territory former USSR per year is less than 10 hours in the south of Central Asia, on the coast Kara Sea- more than 1000 hours. In most 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 urban economy due to the formation of snow drifts on streets and roads, and snow deposition in the wind shadow of buildings in residential areas. In some areas Far East buildings on the leeward side are covered with such a high layer of snow that after the end of the snowstorm it is impossible to get out of them.

Snowstorms complicate the work of air, rail and road transport, and public utilities. Agriculture also suffers from blizzards: with strong winds and a loose structure of the snow cover in the fields, snow is redistributed, areas are exposed, and conditions are created for winter crops to freeze. Blizzards also affect people, creating discomfort when outdoors. Strong winds combined with snow disrupt the rhythm of the breathing process and create difficulties for movement and work. During periods of snowstorms, the so-called meteorological heat losses 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 the biological effect of precipitation 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 that carry pathogenic microbes, are washed out. Convective rainfall contributes to the formation of negative ions in the atmosphere. Thus, in the warm period of the year after a thunderstorm, patients have fewer complaints of a meteopathic nature, and the likelihood of infectious diseases decreases. During 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 for “sunbathing” at this time of year.

At the same time, one cannot fail to note the negative role of precipitation, namely the problem associated with it acid rain. These sediments contain solutions of sulfuric, nitric, hydrochloric and other acids formed from oxides of sulfur, nitrogen, chlorine, etc. emitted during economic activities. As a result of such precipitation, soil and water are polluted. For example, the mobility of aluminum, copper, cadmium, lead and other heavy metals increases, which leads to an increase in their migration ability and transport over long distances. Acid precipitation increases the corrosion of metals, thereby having a negative impact on roofing materials and metal structures of buildings and structures exposed to precipitation.

In areas with a dry or rainy (snowy) climate, precipitation is as important a factor in shaping architecture as solar radiation, wind and temperature regime. Special attention Atmospheric precipitation is taken into account when choosing the design of walls, roofs and building foundations, and selecting building and roofing materials.

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

Accumulation conditions on various surfaces are important mainly for solid precipitation and depend on 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 once every 10 years - 1.5 m. In certain areas of the southern part of Kamchatka average height snow cover can exceed 2 m. The height of snow cover increases with increasing altitude above sea level. Even small elevations affect the depth of snow cover, but the influence of large mountain ranges is especially great.

To clarify snow loads and determine the operating mode 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/m2. In areas with light and unstable snow cover, one heavy snowfall within 24 hours creates a load close to what is possible once every five years. Such snowfalls were observed in Kyiv,

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, canopies over large parking lots, transport hubs).

Fallen snow can be actively redistributed throughout urban areas or in the natural landscape, as well as within the roofs of buildings. In some areas it is blown out, in others it accumulates. The patterns of such redistribution have complex character 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.

Taking into account the amount of snow transported during blizzards is necessary to protect home areas, road networks, automobiles and railways. Data on snowfall is also necessary for planning settlements for the most rational placement of residential and industrial buildings, when developing measures for clearing snow from cities.

The main snow protection measures consist in choosing the most favorable orientation of buildings and road network (RSN), ensuring 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 RSN and residential buildings.

The peculiarities of snow deposition around buildings are that maximum deposits are formed on the leeward and windward sides in front of buildings. “Blowout troughs” are formed immediately in front of the windward facades of buildings and near their corners (Fig. 1.53). It is advisable to take into account the patterns of redeposition of snow cover during snowstorm transfer when placing entrance groups. Entrance areas 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 a microdistrict traditional for the development of modern cities, where the perimeter of the block is formed by 17-story buildings, and inside the block there is a three-story building kindergarten, in the inner areas of the block an extensive snow accumulation zone is formed: snow accumulates at the entrances

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

• - transfer
• - blowing

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

Accumulation

residential buildings and on the territory of a kindergarten. As a result, such an area requires snow removal after each snowfall. In another option, 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 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 residential areas in winter becomes much easier. This option is preferable for areas with active snowstorms.

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

Under the influence of wind, solid precipitation is redistributed along the roof of buildings. Snow accumulating on them creates loads on structures. When designing, these loads should be taken into account and, if possible, the occurrence of snow accumulation areas (snow bags) should be avoided. Part of the precipitation is blown from the roof to 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 coating 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 removal of snow from building coverings 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 ground to the snow load on the cover; ^ - weight of snow cover per 1 m 2 of horizontal surface of the earth, taken in accordance with table. 1.22.

Table 1.22

Weight of snow cover per 1 m 2 of horizontal surface of the earth

Snowy areas*
Snow cover weight, kg/m2

* Accepted according to card 1 of Appendix “G” to the joint venture “Urban Planning”.

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

Thermal coefficient WITH, 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 generation, leading to snow melting, with roof slopes exceeding 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 ground to the snow load on the covering 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 single-pitched and double-pitched roofs, the value of the coefficient p is 1.0 with a roof slope of 60°. Intermediate values ​​are determined by linear interpolation. Thus, when the slope of the coating is more than 60°, the snow is not retained on it and almost all of it slides down under the influence of gravity. Coverings with this slope are widely used in traditional architecture. northern countries, in mountainous areas and during the construction of buildings and structures that do not provide sufficiently strong roof structures - domes and hipped towers with a large span and roofing on 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.

When wind and buildings interact, a redistribution of not only solid but also liquid precipitation occurs. It consists in increasing their number on the windward side of buildings, in the zone of wind flow braking and on the side of the windward corners of buildings, where precipitation contained in additional volumes of air flowing around the building arrives. This phenomenon is associated with waterlogging of walls, wetting of interpanel joints, and deterioration of the microclimate of windward rooms. For example, the windward facade of a typical 17-story 3-section residential building during rain with an average precipitation rate of 0.1 mm/min and a wind speed of 5 m/s intercepts about 50 tons of water per hour. Some of it is spent on wetting the facade and protruding elements, the rest flows down the wall, causing adverse consequences for the local area.

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

During architectural design, questions arise related to assessing the intensity of ice formation on individual parts of buildings. The amount of ice load on them depends on climatic conditions and on technical parameters each object (size, shape, roughness, etc.). Solving issues related to the prevention of ice formations and associated disruptions in 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 design parameters of buildings and structures. Ice-frost deposits of ice are also harmful to tree and shrub vegetation, which forms the basis of landscaping in the urban environment. Under their weight, branches and sometimes tree trunks break. The productivity of orchards is decreasing, and agricultural productivity is decreasing. The formation of ice and black ice on roads creates dangerous conditions for ground transport.

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

Architecture is greatly influenced by the combined effects of wind, sand and dust - dust storms, which also relate to atmospheric phenomena. The combination of winds and dust requires protection of the living environment. The level of non-toxic dust in a home should not exceed 0.15 mg/m 3 , and a value of no more than 0.5 mg/m 3 is taken as the maximum permissible concentration (MAC) for calculations. The intensity of the transfer of sand and dust, as well as snow, depends on wind speed, local features of the relief, the presence of unturfed 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 built-up areas are approximately the same as for snow. Maximum deposits are formed on the leeward and windward sides of the building or their roofs.

The methods for combating this phenomenon are the same as for snow transfer. In areas with high air dust (Kalmykia, Astrakhan region, Caspian part of Kazakhstan, etc.) the following are recommended: a special layout of housing with the main premises oriented to the protected side or with a dust-proof glazed corridor; appropriate layout of neighborhoods; optimal direction of streets, forest protection belts, etc.

Atmospheric precipitation is water in liquid and solid form that falls from clouds and precipitates from the air.

Types of precipitation

There are different classifications for precipitation. A distinction is made between blanket precipitation, which is associated with warm fronts, and rainfall, which is associated with cold fronts.

Precipitation is measured in millimeters - the thickness of the layer of fallen water. On average, high latitudes and deserts receive about 250 mm of precipitation per year, and the globe as a whole receives about 1,000 mm of precipitation per year.

Measuring precipitation is essential for any geographic research. After all, precipitation is one of the most important links in moisture circulation on the globe.

The defining characteristics for a particular climate are considered to be the average monthly, annual, seasonal and long-term amount of precipitation, its daily and annual cycle, its frequency and intensity.

These indicators are extremely important for most sectors of the national (agricultural) economy.

Rain is liquid precipitation - in the form of drops from 0.4 to 5-6 mm. Raindrops can leave a mark in the form of a wet spot on a dry object, or on the surface of water - in the form of a diverging circle.

There are different types rain: icy, freezing and rain with snow. Both freezing rain and ice rain fall at subzero air temperatures.

Supercooled rain is characterized by liquid precipitation, the diameter of which reaches 5 mm; After this type of rain, ice may form.

And freezing rain is represented by precipitation in a solid state - these are ice balls with frozen water inside. Snow is precipitation that falls in the form of flakes and snow crystals.

Horizontal visibility depends on the intensity of snowfall. A distinction is made between sleet and sleet.

The concept of weather and its features

The state of the atmosphere in a particular place at a particular time is called weather. Weather is the most variable phenomenon in environment. It will start to rain, then the wind will start, and after a few hours the sun will shine and the wind will subside.

But even the variability of weather has its own patterns, despite the fact that the formation of weather is influenced by a huge number of factors.

The main elements characterizing the weather include the following meteorological indicators: solar radiation, atmospheric pressure, air humidity and temperature, precipitation and wind direction, wind strength and cloudiness.

If we talk about weather variability, then most often it changes in temperate latitudes - in regions with continental climate. And the most stable weather occurs in polar and equatorial latitudes.

Changes in weather are associated with changes in seasons, that is, changes are periodic, and weather conditions repeat over time.

Every day we observe the daily change in weather - night follows day, and for this reason weather conditions change.

Climate concept

The long-term weather pattern is called climate. Climate is determined in a specific area - thus, the weather pattern must be stable for a certain geographical location.

Classification of precipitation. By type, precipitation is divided into liquid, solid and ground.

Liquid precipitation includes:

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, seemingly in suspension.

Solid sediments include:

snow - ice crystals that form various kinds 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 pellets - precipitation in the form of opaque spherical grains of white or matte white (milky) color with a diameter of 2 to 5 mm;

ice pellets are solid particles that are transparent on the surface and have 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), having a spherical or irregular shape and a complex internal structure. The diameter of hailstones varies within a very wide range: from 5 mm to 5–8 cm. There are cases when hailstones weighing 500 g or more fell.

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

dew - tiny drops of water that condense on the horizontal surfaces of objects (decks, boat covers, etc.) due to radiation cooling them on clear cloudless nights. A slight wind (0.5–10 m/s) promotes the formation of dew. If the temperature of horizontal surfaces is below zero, then under similar conditions water vapor sublimates on them and frost forms - a thin layer of ice crystals;

liquid deposit – tiny drops of water or a continuous film of water, formed in cloudy and windy weather on the windward predominantly vertical surfaces of cold objects (walls of superstructures, protective devices of winches, cranes, etc.).

glaze is an ice crust that forms when the temperature of these surfaces is below 0 °C. In addition, a hard coating may 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 low winds, granular or crystalline frost may form on the vessel's equipment, ledges, cornices, wires, etc. Unlike frost, rime does not form on horizontal surfaces. The loose structure of frost distinguishes it from solid plaque. Granular rime is formed at air temperatures from -2 to -7 ° C due to freezing on the subject of supercooled fog droplets, and crystalline rime, which is a white precipitate of crystals of a fine structure, is formed at night with a cloudless sky or thin clouds from particles of fog or haze at a temperature from –11 to –2 °C and above.

According to the nature of precipitation, precipitation is divided into shower, heavy and drizzling.

Rainfall falls from cumulonimbus (thunderstorm) clouds. In summer it is large drops of rain (sometimes with hail), and in winter it is heavy snowfall with frequent changes in the shape of snowflakes, snow or ice grains. Precipitation occurs from nimbostratus (summer) and altostratus (winter) clouds. They are characterized by small fluctuations in intensity and long duration of fallout.

Drizzle falls from stratus and stratocumulus clouds in the form of small drops with a diameter of no more than 0.5 mm, descending at very low speeds.

Based on intensity, precipitation is divided into strong, moderate and light.

Clouds and precipitation.

Upper level clouds.

Cirrus (Ci) – Russian name feathery, individual tall, thin, fibrous, white, often silky clouds. Their fibrous and feathery appearance is due to the fact that they are composed of ice crystals.

Cirrus appear in the form of isolated bunches; long, thin lines; feathers like smoke torches, curved stripes. Cirrus clouds can appear in parallel bands that cross the sky and appear to converge on a single point on the horizon. This will be the direction of the low pressure area. Because of their height, they become illuminated earlier than other clouds in the morning and remain illuminated after the Sun has set. Cirrus are generally associated with clear weather, but if they are followed by lower and denser clouds, then there may be rain or snow in the future.

Cirrocumulus (Cc) , the Russian name for cirrocumulus, are tall clouds made up of small white flakes. Usually they do not reduce illumination. They are placed in the sky in separate groups of parallel lines, often like ripples, similar to sand on the coast or waves on the sea. Cirrocumulus are composed of ice crystals and are associated with clear weather.

Cirrostratus (Cs), The Russian name is cirrostratus - thin, white, high clouds, sometimes covering the sky completely and giving it a milky tint, more or less distinct, reminiscent of a thin tangled network. The ice crystals they are made of refract light to form a halo with the Sun or Moon at the center. If the clouds subsequently thicken and lower, precipitation can be expected in about 24 hours. These are the clouds of a warm front system.

Upper level clouds do not produce precipitation.

Mid-level clouds. Precipitation.

Altocumulus (Ac), Russian name altocumulus,- middle-tier clouds, consisting of a layer of large individual spherical masses. Altocumulus (Ac) are similar to the upper level clouds of sirrocumulus. Since they lie lower, their density, water content and the size of individual structural elements are greater than those of sirrocumulus. Altocumulus (Ac) can vary in thickness. They can range from blinding white if they are illuminated by the Sun, to dark gray if they cover the entire sky. They are often mistaken for stratocumulus. Sometimes individual structural elements merge and form a series of large swells, like ocean waves, with stripes of blue sky between them. These parallel stripes differ from cirrocumulus in that they appear on the palate in large dense masses. Sometimes altocumulus appear before a thunderstorm. As a rule, they do not produce precipitation.

Altostratus (As) , Russian name altostratified, - middle-tier clouds that look like a gray fibrous layer. The Sun or Moon, if visible, appears as if through frosted glass, often with crowns around the star. Halos do not form in these clouds. If these clouds thicken, lower, or turn into low ragged Nimbostratus, then precipitation begins to fall from them. Then you should expect prolonged rain or snow (for several hours). In the warm season, drops from altostratus, evaporating, do not reach the surface of the earth. In winter they can produce significant snowfalls.

Low level clouds. Precipitation.

Stratocumulus (Sc) Russian name stratocumulus– low clouds that look like soft, gray masses, like waves. They can be formed into long, parallel shafts similar to altocumulus. Sometimes precipitation falls from them.

Stratus (St), The Russian name is stratified - low, homogeneous clouds resembling fog. Often their lower boundary is at an altitude of no more than 300 m. The curtain of dense stratus gives the sky a hazy appearance. They can lie on the very surface of the earth and are then called fog. Stratus can be dense and transmit sunlight so poorly that the Sun is not visible at all. They cover the Earth like a blanket. If you look from above (having broken through the thickness of the clouds on an airplane), they are dazzlingly white illuminated by the sun. Strong winds sometimes tear the stratus into pieces, called stratus fractus.

Lungs can fall out of these clouds in winter ice needles, and in the summer - drizzle– very small droplets suspended in the air and gradually settling. Drizzle comes from continuous low stratus or from those lying on the surface of the Earth, that is, from fog. Fog is very dangerous in navigation. Freezing drizzle can cause icing on the boat.

Nimbostratus (Ns) , Russian name for stratostratus, - low, dark. Stratus, shapeless clouds, almost uniform, but sometimes with damp patches at the base. Nimbostratus usually cover vast territories measured in hundreds of kilometers. Throughout this vast territory there is simultaneously snow or rain. Precipitation falls for long hours (up to 10 hours or more), drops or snowflakes are small in size, the intensity is low, but during this time a significant amount of precipitation can fall. They are called cover. Similar precipitation may also fall from Altostratus, and sometimes from Stratocumulus.

Clouds of vertical development. Precipitation.

Cumulus (Cu) . Russian name cumulus, - dense clouds formed in vertically rising air. As the air rises, it cools adiabatically. When its temperature reaches the dew point, condensation begins and a cloud appears. Cumulus have a horizontal base, convex top and side surfaces. Cumulus appear as separate flakes and never cover the palate. When the vertical development is small, the clouds look like tufts of cotton wool or cauliflower. Cumulus are called "fair weather" clouds. They usually appear by midday and disappear by evening. However, Cu can merge with altocumulus, or grow and turn into thunderous cumulonimbus. Cumulus are distinguished by high contrast: the white, illuminated by the Sun, and the shadow side.

Cumulonimbus (Cb), Russian name cumulonimbus, - massive clouds of vertical development, rising in huge columns to great heights. These clouds begin in the lowest tier and extend to the tropopause, and sometimes extend into the lower stratosphere. They are taller than the highest mountains on Earth. Their vertical thickness is especially great in equatorial and tropical latitudes. The upper part of Cumulonimbus is composed of ice crystals, often stretched by the wind in an anvil shape. At sea, the top of the cumulonimbus can be visible at a great distance, when the base of the cloud is still below the horizon.

Cumulus and cumulonimbus are called clouds of vertical development. They are formed as a result of thermal and dynamic convection. On cold fronts, cumulonimbus arise as a result of dynamic convection.

These clouds can appear in the cold air at the rear of the cyclone and at the front of the anticyclone. Here they are formed as a result of thermal convection and give, accordingly, intramass, local rainfall. Cumulonimbus and associated showers over the oceans occur more often at night, when the air above the water surface is thermally unstable.

Particularly powerful cumulonimbus develop in the intertropical convergence zone (near the equator) and in tropical cyclones. Associated with cumulonimbus are: atmospheric phenomena like rain showers, snow showers, snow pellets, thunderstorms, hail, rainbows. It is with cumulonimbus that waterspouts (tornadoes) are associated, the most intense and most often observed in tropical latitudes.

Shower rain (snow) characterized by large drops (snow flakes), sudden onset, sudden end, significant intensity and short duration (from 1-2 minutes to 2 hours). Rain showers in summer are often accompanied by thunderstorms.

Ice grains It is a hard, opaque piece of ice up to 3 mm in size, moist on top. Ice pellets fall with heavy rain in spring and autumn.

Snow pellets has the appearance of opaque soft grains of white branches from 2 to 5 mm in diameter. Snow pellets are observed when the wind is squally. Snow pellets are often observed simultaneously with heavy snow.

hail falls only in the warm season exclusively during showers and thunderstorms of their most powerful cumulonimbus and usually lasts no more than 5-10 minutes. These are pieces of ice with a layered structure, about the size of a pea, but there are also many larger sizes.

Other precipitation.

Precipitation in the form of drops, crystals or ice on the surface of the Earth or objects is often observed, not falling from clouds, but precipitating from the air under a cloudless sky. This is dew, frost, frost.

Dew drops that appear on the deck at night in summer. At negative temperatures it forms frost. Frost - ice crystals on wires, ship equipment, racks, yards, masts. Frost forms at night, more often when there is fog or haze, at air temperatures below -11°C.

Ice an extremely dangerous phenomenon. It is an ice crust that results from the freezing of supercooled fog, drizzle, raindrops or droplets on supercooled objects, especially on windward surfaces. A similar phenomenon occurs from splashing or flooding of the deck. sea ​​water at negative air temperatures.

Determining cloud height.

At sea, cloud heights are often determined approximately. This is a difficult task, especially at night. The height of the lower base of vertical clouds (any variety of cumulus), if they were formed as a result of thermal convection, can be determined from psychrometer readings. The height to which the air must rise before condensation begins is proportional to the difference between the air temperature t and the dew point td. At sea, this difference is multiplied by 126.3 and the height of the lower boundary of cumulus clouds is obtained N in meters. This empirical formula looks like:

H = 126.3 ( t – t d ). (4)

The height of the base of lower layer stratus clouds ( St, Sc, Ns) can be determined using empirical formulas:

H = 215 (t – t d ) (5)

H = 25 (102 - f); (6)

Where f – relative humidity.

Visibility. Fogs.

Visibility This is the maximum horizontal distance at which an object can be clearly visible and recognized in daylight. In the absence of any impurities in the air, it is up to 50 km (27 nautical miles).

Visibility is reduced due to the presence of liquid and solid particles in the air. Visibility is impaired by smoke, dust, sand, and volcanic ash. This occurs when there is fog, smog, haze, or precipitation. The visibility range decreases due to splashes in the sea in stormy weather with a wind force of 9 or more (40 knots, about 20 m/s). Visibility becomes worse during low, continuous clouds and at dusk.

Haze

Haze is a clouding of the atmosphere due to solid particles suspended in it, such as dust, as well as smoke, burning, etc. With severe haze, visibility is reduced to hundreds, and sometimes to tens of meters, as in dense fog. Haze is usually a consequence of dust (sand) storms. Even relatively large particles are lifted into the air by strong winds. This is a typical phenomenon of deserts and plowed steppes. Large particles spread in the lowest layer and settle near their source. Small particles are carried over long distances by air currents, and due to air turbulence they penetrate upward to a considerable height. Fine dust remains in the air for a long time, often in the complete absence of wind. The color of the Sun becomes brownish. The relative humidity during these events is low.

Dust can be transported over long distances. It was celebrated in the Greater and Lesser Antilles. Dust from the Arabian deserts is carried by air currents into the Red Sea and the Persian Gulf.

However, during haze, visibility is never as bad as during fog.

Fogs. General characteristics.

Fogs pose one of the greatest dangers to navigation. They are responsible for many accidents, human lives, and sunken ships.

Fog is said to occur when horizontal visibility, due to the presence of droplets or water crystals in the air, becomes less than 1 km. If visibility is more than 1 km, but not more than 10 km, then such a decrease in visibility is called haze. Relative humidity during fog is usually more than 90%. Water vapor itself does not reduce visibility. Visibility is reduced by water droplets and crystals, i.e. water vapor condensation products.

Condensation occurs when the air is oversaturated with water vapor and the presence of condensation nuclei. Above the sea it is mainly small particles of sea salt. Supersaturation of air with water vapor occurs when the air is cooled or in cases of additional supply of water vapor, and sometimes as a result of mixing of two air masses. In accordance with this, fogs are distinguished cooling, evaporation and mixing.

Based on intensity (based on the visual range D n), fogs are divided into:

strong D n 50 m;

moderate 50 m<Д n <500 м;

weak 500 m<Д n < 1000 м;

heavy haze 1000 m<Д n <2000 м;

light haze 2000 m<Д n <10 000 м.

Based on their state of aggregation, fogs are divided into droplet-liquid, icy (crystalline) and mixed. Visibility conditions are worst in icy fogs.

Cooling mists

Water vapor condenses as the air cools to its dew point. This is how cooling fogs are formed - the largest group of fogs. They can be radiative, advective and orographic.

Radiation mists. The Earth's surface emits long-wave radiation. During the day, energy losses are offset by the arrival of solar radiation. At night, radiation causes the Earth's surface temperature to drop. On clear nights, the cooling of the underlying surface occurs more intensely than in cloudy weather. The air adjacent to the surface also cools. If the cooling is to the dew point and below, then dew will form in calm weather. A weak wind is required for fog to form. In this case, as a result of turbulent mixing, a certain volume (layer) of air is cooled and condensation forms in this layer, i.e. fog. Strong wind leads to mixing of large volumes of air, dispersion of condensate and its evaporation, i.e. to the disappearance of the fog.

Radiation fog can extend up to a height of 150 m. It reaches its maximum intensity before or shortly after sunrise, when the minimum air temperature occurs. Conditions necessary for the formation of radiation fog:

High air humidity in the lower layers of the atmosphere;

Stable stratification of the atmosphere;

Partly cloudy or clear weather;

Light wind.

The fog disappears as the earth's surface warms up after sunrise. The air temperature rises and the droplets evaporate.

Radiation mists above the water surface are not formed. Daily fluctuations in the temperature of the water surface, and therefore the air, are very small. The temperature at night is almost the same as during the day. Radiative cooling does not occur, and there is no condensation of water vapor. However, radiation fogs can cause problems in navigation. In coastal areas, fog, as a single whole, flows with cold, and therefore heavy, air onto the water surface. This can also be amplified by night breezes from land. Even clouds formed at night over elevated coasts can be carried by the night breeze to the surface of the water, as is observed on many coasts of temperate latitudes. The cloud cap from the hill often flows down, covering the approaches to the shore. More than once this led to a collision between ships (port of Gibraltar).

Advection fogs. Advective fogs result from the advection (horizontal transfer) of warm, moist air onto a cold underlying surface.

Advective fogs can simultaneously cover vast horizontal spaces (many hundreds of kilometers), and vertically extend up to 2 kilometers. They do not have a daily cycle and can exist for a long time. Over land at night they intensify due to radiation factors. In this case, they are called advective-radiative. Advective fogs also occur with significant winds, provided that the air stratification is stable.

These fogs are observed over land in the cold season when relatively warm and humid air enters it from the water surface. This phenomenon occurs in Foggy Albion, Western Europe, and coastal areas. In the latter case, if fogs cover relatively small areas, they are called coastal.

Advective fogs are the most common fogs in the ocean, occurring near the coasts and in the depths of the oceans. They always stand above cold currents. In the open sea, they can also be found in warm sectors of cyclones, in which air is transported from warmer areas of the ocean.

They can be found off the coast at any time of the year. In winter, they form over land and can partially slide to the water surface. In summer, advective fogs occur off the coast in cases where warm, moist air from the continent, in the process of circulation, passes to a relatively cold water surface.

Signs of the imminent disappearance of advective fog:

- change in wind direction;

- disappearance of the warm sector of the cyclone;

- it started to rain.

Orographic fogs. Orographic fogs or slope fogs are formed in mountainous areas with a low-gradient pressure field. They are associated with the valley wind and are observed only during the day. The air rises up the slope with the valley wind and is cooled adiabatically. Once the temperature reaches the dew point, condensation begins and a cloud forms. For residents of the slope it will be fog. Sailors can encounter such fogs off the mountainous coasts of islands and continents. Fogs can obscure important landmarks on the slopes.

Mists of evaporation

Condensation of water vapor can occur not only as a result of cooling, but also when the air is oversaturated with water vapor due to evaporation of water. The evaporating water should be warm and the air cold, the temperature difference should be at least 10 °C. Cold air stratification is stable. In this case, an unstable stratification is established in the lowest driving layer. This causes a large amount of water vapor to flow into the atmosphere. It will immediately condense in the cold air. A fog of evaporation appears. Often it is small vertically, but its density is very high and, accordingly, visibility is very poor. Sometimes only the masts of the ship stick out from the fog. Such fogs are observed over warm currents. They are characteristic of the Newfoundland region, at the junction of the warm Gulf Stream and the cold Labrador Current. This is an area of ​​heavy shipping.

In the Gulf of St. Lawrence, fog sometimes extends vertically up to 1500m. At the same time, the air temperature can be below 9°C below zero and the wind is almost gale force. The fog in such conditions consists of ice crystals and is dense with very poor visibility. Such dense sea fogs are called frost smoke or arctic frost smoke and pose a serious danger.

At the same time, with unstable air stratification, there is a slight local hovering of the sea, which does not pose a danger to navigation. The water seems to be boiling, streams of “steam” rise above it and immediately dissipate. Such phenomena occur in the Mediterranean Sea, off Hong Kong, in the Gulf of Mexico (with the relatively cold north wind “Norther”) and in other places.

Mixing mists

Fog can also form when two air masses mix, each of which has high relative humidity. The reservoir may be oversaturated with water vapor. For example, if cold air meets warm and humid air, the latter will cool at the mixing boundary and fog may appear there. Fog ahead of a warm front or occluded front is common in temperate and high latitudes. This mixing fog is known as frontal fog. However, it can also be considered as evaporation fog, since it occurs when warm droplets evaporate in cold air.

Mixing fogs form at the edge of ice and above cold currents. An iceberg in the ocean can be surrounded by fog if there is enough water vapor in the air.

Geography of fogs

The type and shape of clouds depend on the nature of the prevailing processes in the atmosphere, the season of the year and the time of day. Therefore, much attention is paid to observations of the development of clouds over the sea when sailing.

There are no fogs in the equatorial and tropical regions of the oceans. It’s warm there, there are no differences in temperature and air humidity day and night, i.e. There is almost no daily variation of these meteorological quantities.

There are a few exceptions. These are vast areas off the coast of Peru (South America), Namibia (South Africa) and off Cape Guardafui in Somalia. In all these places it is observed upwelling(rising of cold deep waters). Warm, moist air from the tropics flows over cold water and forms advective fog.

Fogs in the tropics can occur near continents. Thus, the port of Gibraltar has already been mentioned; fog is possible in the port of Singapore (8 days a year); in Abidjan there are up to 48 days of fog. Their greatest number is in the Bay of Rio de Janeiro - 164 days a year.

In temperate latitudes, fogs are a very common phenomenon. Here they are observed off the coast and in the depths of the oceans. They occupy vast territories and occur in all seasons of the year, but are especially frequent in winter.

They are also typical for polar regions near the boundaries of ice fields. In the North Atlantic and the Arctic Ocean, where the warm waters of the Gulf Stream penetrate, there is constant fog during the cold season. They are often found at the ice edge in summer.

Fogs most often occur at the junction of warm and cold currents and in places where deep water rises. The frequency of fogs is also high along the coasts. In winter, they occur when warm, moist air advects from the ocean onto land, or when cold continental air flows down onto relatively warm water. In the summer, air from the continent hitting the relatively cold water surface also produces fog.

Precipitation

Precipitation

water in a liquid or solid state that falls from clouds or settles from the air onto the earth's surface. Precipitation brings to the land surface all the water involved in water exchange processes (with the exception of certain areas where water comes from underground sources or through watercourses - but it was also previously brought to land by precipitation). The vast majority of precipitation ( rain, drizzle, snow, snowy and icy cereal, hail, freezing rain, etc.) falls from clouds. Released directly from the air dew, frost, hard coating, frost etc. Precipitation is measured in the thickness of the layer of water (usually expressed in millimeters) that falls per unit time. For various purposes, precipitation data for an hour, day, month, year, etc. is used. Usually the amount of precipitation over a short period of time (s, min, h) is also called precipitation intensity. On Wed. approx. falls on Earth per year. 1000 mm, minimum in tropical deserts (Atacama in Chile, some regions of the Sahara, etc.) - no more than 10 mm per year (often there is no precipitation at all for several years in a row) and maximum in the monsoon region in the foothills Himalayas (Cherrapunji) - Wed. OK. 11 thousand mm per year (the maximum precipitation per year that fell there is more than 20 thousand mm). The highest recorded amount of precipitation per day (1870 mm) fell in the form of rain on the island. Reunion in the Indian Ocean in March 1952 during the passage of a tropical cyclone. Excess rainfall over several hours or days leads to floods, landslides, mudflows and other disasters, and a deficiency within a few weeks or the first months will lead to drought.

Geography. Modern illustrated encyclopedia. - M.: Rosman. Edited by prof. A. P. Gorkina. 2006 .

Synonyms:

See what “precipitation” is in other dictionaries:

PRECIPITATION, in meteorology, all forms of water, liquid or solid, falling from the atmosphere to the ground. Precipitation differs from CLOUDS, FOG, DEW and FROST in that it falls and reaches the ground. Includes rain, drizzle, SNOW and HAIL. Measured by layer thickness... ... Scientific and technical encyclopedic dictionary

Modern encyclopedia

Atmospheric water in a liquid or solid state (rain, snow, cereals, ground hydrometeors, etc.), falling from clouds or deposited from the air on the earth's surface and on objects. Precipitation is measured by the thickness of the layer of fallen water in mm. IN… … Big Encyclopedic Dictionary

Groats, snow, drizzle, hydrometeor, lotions, rain Dictionary of Russian synonyms. precipitation noun, number of synonyms: 8 hydrometeor (6) ... Dictionary of synonyms

Precipitation- atmospheric, see Hydrometeors. Ecological encyclopedic dictionary. Chisinau: Main editorial office of the Moldavian Soviet Encyclopedia. I.I. Dedu. 1989. Precipitation, water coming from the atmosphere to the surface of the earth (in liquid or solid... Ecological dictionary

Precipitation- atmospheric, water in a liquid or solid state falling from clouds (rain, snow, pellets, hail) or deposited on the earth's surface and objects (dew, frost, hoarfrost) as a result of condensation of water vapor in the air. Precipitation is measured... ... Illustrated Encyclopedic Dictionary

In geology, loose formations deposited in a suitable environment as a result of physical, chemical and biological processes... Geological terms

PRECIPITATION, ov. Atmospheric moisture falling to the ground in the form of rain or snow. Abundant, weak o. Today there will be no precipitation (no rain, no snow). | adj. sedimentary, oh, oh. Ozhegov's explanatory dictionary. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 … Ozhegov's Explanatory Dictionary

- (meteor.). This name is usually used to denote the moisture that falls on the surface of the earth, being separated from the air or from the soil in dropwise liquid or solid form. This release of moisture occurs every time water vapor constantly... ... Encyclopedia of Brockhaus and Efron

1) atmospheric water in a liquid or solid state, falling from clouds or depositing from the air on the surface of the earth and on objects. O. falls from clouds in the form of rain, drizzle, snow, sleet, snow and ice pellets, snow grains,... ... Dictionary of emergency situations

PRECIPITATION- meteorological, liquid and solid bodies released from the air onto the surface of the soil and solid objects due to the thickening of water vapor contained in the atmosphere. If O. falls from a certain height, then the result is hail and snow; if they... ... Great Medical Encyclopedia

Books

• Precipitation and thunderstorms from December 1870 to November 1871, A. Voeikov. Reproduced in the original author's spelling of the 1875 edition (St. Petersburg publishing house). IN…