Types of natural precipitation and various. What is precipitation? Definition and types

Water molecules continuously evaporate from the surface of lakes, seas, rivers and oceans - 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 the amount of it.

Air humidity varies in all areas globe, in hot weather it increases when evaporation from the surface of reservoirs into the atmosphere increases. Low humidity is usually found over desert areas because there is little water vapor, so the air in deserts is very dry.

Water vapor goes through many tests 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 are much lighter than cold ones, they rise. Tiny water droplets that formed in the air continue to travel with it into in the form of precipitation.

Types of precipitation, fog and clouds.

To imagine how further transformation of water vapor occurs in the atmosphere, you can conduct a fairly simple experiment. You need 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 drops will form on it. The released steam turned into water, which means that a phenomenon called condensation occurred.

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

When flying on an airplane, you can see how clouds sometimes appear below the aircraft. Or you can even find yourself among the clouds if you climb a high mountain in low clouds. At this moment, surrounding objects and people will turn into invisible beings, 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 drops are no longer able to stay in the air, then rain pours from thunderclouds onto the ground. in the form of precipitation.

Dew and frost as types of precipitation.

Near bodies of water in summer, a lot of steam forms in the air and it becomes highly 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 drops are visible covering various objects.

With coming late autumn the temperature overnight 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 glass in the form of frosty patterns of extraordinary beauty. Sometimes frost simply covers the surface of the earth, like a thin layer of snow. The fantastic patterns formed by frost are best seen on rough surfaces, such as:

• tree branches;
• loose ground surface;
• wooden benches.

Snow and hail as types of precipitation.

Pieces of ice are called hail irregular shape, which fall to the ground with rain in summer. There is also “dry” hail, which falls without rain. If you carefully cut a hailstone, you will see on the cut that it consists of alternating opaque and transparent layers.

When air currents carry water vapor to a height of about 5 km, then water droplets begin to settle on the dust particles, and they instantly freeze. The resulting ice crystals begin to increase in size, and when they reach heavy weight I'm starting to fall. But a new stream of warm air emanates from the ground and it returns them back to the cold cloud. The hailstones begin to grow again and try to fall, this process is repeated several times, as soon as they have collected enough heavy weight they fall to the ground.

The size of these types of precipitation(hailstones) usually range from 1 to 5 mm in diameter. Although there have been cases when the size of hailstones exceeded a chicken egg, and the weight reached approximately 400-800 g.

Hail can cause great damage to agriculture; it damages vegetable gardens and crops, and also leads to the death of small animals. Large hailstones can damage cars and even pierce aircraft skins.

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, the earth is enveloped in a snow-white blanket consisting of tiny ice crystals called snow. Due to low temperatures, water droplets freeze and ice crystals form in the clouds, then new water molecules attach to them and, as a result, a separate snowflake is born. All snowflakes have six corners, but the patterns woven on them by frost differ from each other. When snowflakes are exposed to wind currents, they stick together and form snow flakes. Walking through the snow in frosty weather, we often hear crunching noises under our feet, as ice crystals break in the snowflakes.

Such types of precipitation, as snow brings many problems, traffic on roads becomes difficult due to snow, power lines break under its weight, and melting snow leads to floods. But due to the fact that the plants are covered with a blanket of snow, they are able to withstand even severe frosts.

Precipitation Atmospheric precipitation is water in a droplet-liquid (rain, drizzle) and solid (snow, pellets, hail) state, falling from clouds or depositing directly from the air onto the surface of the Earth and objects (dew, drizzle, frost, ice) as a result of condensation of water vapor, in the air.

Atmospheric precipitation is also the amount of water that fell in a certain place over a certain period of time (usually measured by the thickness of the layer of fallen water in mm). Magnitude atmospheric precipitation depends on air temperature, atmospheric circulation, relief, sea currents.

A distinction is made between blanket precipitation, associated primarily with warm fronts, and rainfall, associated primarily with cold fronts. Precipitation deposited from the air: dew, frost, frost, ice.

Precipitation is measured by the thickness of the layer of fallen water in millimeters. On average, the globe receives approx. 1000 mm of precipitation per year: from 2500 mm in humid equatorial forests up to 10 mm in deserts and 250 mm in high latitudes. Precipitation is measured by rain gauges, precipitation gauges, pluviographs at meteorological stations, and for large areas - using radar.

Classification of precipitation

Precipitation falling on earth's surface

Cover precipitation- characterized by monotony of loss without significant fluctuations in intensity. They start and stop gradually. The duration of continuous precipitation is usually several hours (and sometimes 1-2 days), but in some cases light precipitation can last half an hour to an hour. Usually fall from nimbostratus or altostratus clouds; Moreover, in most cases the cloudiness is continuous (10 points) and only occasionally significant (7-9 points, usually at the beginning or end of the precipitation period). Sometimes weak short-term (half an hour to an hour) precipitation is observed from stratus, stratocumulus, altocumulus clouds, with the number of clouds being 7-10 points. In frosty weather (air temperature below −10...-15°), light snow may fall from a partly cloudy sky.

Rain- liquid precipitation in the form of droplets with a diameter of 0.5 to 5 mm. Individual raindrops leave a mark on the surface of water in the form of a diverging circle, and on the surface of dry objects - in the form of a wet spot.

Freezing rain- liquid precipitation in the form of drops with a diameter of 0.5 to 5 mm, falling at negative air temperatures (most often 0...-10°, sometimes up to −15°) - falling on objects, the drops freeze and ice forms.

freezing rain- solid precipitation that falls at negative air temperatures (most often 0...-10°, sometimes up to −15°) in the form of solid transparent ice balls with a diameter of 1-3 mm. There is unfrozen water inside the balls - when falling on objects, the balls break into shells, the water flows out and ice forms.

Snow- solid precipitation that falls (most often at negative air temperatures) in the form of snow crystals (snowflakes) or flakes. With light snow, horizontal visibility (if there are no other phenomena - haze, fog, etc.) is 4-10 km, with moderate snow 1-3 km, with heavy snow - less than 1000 m (in this case, snowfall increases gradually, so Visibility values ​​of 1-2 km or less are observed no earlier than an hour after the start of snowfall). In frosty weather (air temperature below −10...-15°), light snow may fall from a partly cloudy sky. Separately, the phenomenon of wet snow is noted - mixed precipitation that falls at positive air temperatures in the form of flakes of melting snow.

Rain with snow- mixed precipitation that falls (most often at positive air temperatures) in the form of a mixture of drops and snowflakes. If rain and snow fall at subzero air temperatures, precipitation particles freeze onto objects and ice forms.

Drizzle- characterized by low intensity, monotony of loss without changing intensity; start and stop gradually. The duration of continuous loss is usually several hours (and sometimes 1-2 days). Fall out of stratus clouds or fog; Moreover, in most cases the cloudiness is continuous (10 points) and only occasionally significant (7-9 points, usually at the beginning or end of the precipitation period). Often accompanied by decreased visibility (haze, fog).

Drizzle- liquid precipitation in the form of very small drops (less than 0.5 mm in diameter), as if floating in the air. A dry surface becomes wet slowly and evenly. When deposited on the surface of the water, it does not form diverging circles on it.

Freezing drizzle- liquid precipitation in the form of very small drops (with a diameter of less than 0.5 mm), as if floating in the air, falling at negative air temperatures (most often 0 ... -10 °, sometimes up to −15 °) - settling on objects, the drops freeze and form ice

Snow grains- solid precipitation in the form of small opaque white particles (sticks, grains, grains) with a diameter of less than 2 mm, falling at negative air temperatures.

Rainfall- characterized by the suddenness of the beginning and end of the loss, a sharp change in intensity. The duration of continuous loss usually ranges from several minutes to 1-2 hours (sometimes several hours, in the tropics - up to 1-2 days). Often accompanied by a thunderstorm and a short-term increase in wind (squall). They fall from cumulonimbus clouds, and the amount of clouds can be both significant (7-10 points) and small (4-6 points, and in some cases even 2-3 points). The main feature of precipitation of a torrential nature is not its high intensity (storm precipitation can be weak), but the very fact of precipitation from convective (most often cumulonimbus) clouds, which determines fluctuations in the intensity of precipitation. IN hot weather light showers can fall from powerful cumulus clouds, and sometimes (very light showers) even from mid cumulus clouds.

shower rain- torrential rain.

Shower snow- shower snow. It is characterized by sharp fluctuations in horizontal visibility from 6-10 km to 2-4 km (and sometimes up to 500-1000 m, in some cases even 100-200 m) over a period of time from several minutes to half an hour (snow “charges”).

Shower rain with snow- mixed rainfall precipitation, falling (most often at positive air temperatures) in the form of a mixture of drops and snowflakes. If heavy rain with snow falls at sub-zero air temperatures, precipitation particles freeze onto objects and ice forms.

Snow pellets- solid precipitation of a storm nature, falling at an air temperature of about zero degrees and having the appearance of opaque white grains with a diameter of 2-5 mm; The grains are fragile and easily crushed by fingers. Often falls before or simultaneously with heavy snow.

Ice grains- solid rainfall precipitation, falling at air temperatures from −5 to +10° in the form of transparent (or translucent) ice grains with a diameter of 1-3 mm; in the center of the grains there is an opaque core. The grains are quite hard (they can be crushed with your fingers with some effort), and when they fall on a hard surface they bounce off. In some cases, the grains may be covered with a film of water (or fall out along with droplets of water), and if the air temperature is below zero, then falling on objects, the grains freeze and ice forms.

hail- solid precipitation that falls in the warm season (at air temperatures above +10°) in the form of pieces of ice various shapes and size: usually the diameter of hailstones is 2-5 mm, but in some cases individual hailstones reach the size of a pigeon or even a chicken egg (then the hail causes significant damage to vegetation, car surfaces, breaks window glass, etc.). The duration of hail is usually short - from 1-2 to 10-20 minutes. In most cases, hail is accompanied by rain showers and thunderstorms.

Unclassified precipitation

Ice needles- solid precipitation in the form of tiny ice crystals floating in the air, formed in frosty weather (air temperature below −10…-15°). During the day they sparkle in the light of the sun's rays, at night - in the rays of the moon or in the light of lanterns. Quite often, ice needles form beautiful glowing “pillars” at night, extending from the lanterns upward into the sky. They are most often observed in clear or partly cloudy skies, sometimes falling from cirrostratus or cirrus clouds. Ice needles

Precipitation formed on the surface of the earth and on the surface metax

Dew- water droplets formed on the surface of the earth, plants, objects, roofs of buildings and cars as a result of condensation of water vapor contained in the air at positive air and soil temperatures, partly cloudy skies and weak winds. Most often observed at night and early morning hours, and may be accompanied by haze or fog. Heavy dew can cause measurable amounts of precipitation (up to 0.5 mm per night), draining water from roofs onto the ground.

Frost- a white crystalline sediment formed on the surface of the earth, grass, objects, roofs of buildings and cars, snow cover as a result of sublimation of water vapor contained in the air at negative soil temperatures, partly cloudy skies and weak winds. It is observed in the evening, night and morning hours, and may be accompanied by haze or fog. In fact, it is an analogue of dew, formed at negative temperatures. On tree branches and wires, frost is deposited weakly (unlike frost) - on the wire of an ice machine (diameter 5 mm), the thickness of frost deposits does not exceed 3 mm.

Crystal frost- a white crystalline sediment consisting of small, fine-structured shiny particles of ice, formed as a result of sublimation of water vapor contained in the air on tree branches and wires in the form of fluffy garlands (easily crumbling when shaken). It is observed in lightly cloudy (clear, or clouds of the upper and middle tier, or broken-stratified) frosty weather (air temperature below −10...-15°), with haze or fog (and sometimes without them) with weak wind or calm. Frost deposits usually occur over several hours at night; during the day, it gradually crumbles under the influence of sunlight, but in cloudy weather and in the shade it can persist throughout the day. On the surface of objects, roofs of buildings and cars, frost is deposited very weakly (unlike frost). However, frost is often accompanied by frost.

Grainy frost- white loose snow-like sediment formed as a result of the settling of small droplets of supercooled fog on tree branches and wires in cloudy, foggy weather (at any time of the day) at air temperatures from zero to −10° and moderate or strong wind. When fog droplets become larger, it can turn into ice, and when the air temperature drops in combination with weakening winds and a decrease in the amount of clouds at night, it can turn into crystalline frost. The growth of grainy frost continues as long as the fog and wind last (usually several hours, and sometimes several days). The deposited granular frost may persist for several days.

Ice- a layer of dense glassy ice (smooth or slightly lumpy), formed on plants, wires, objects, the surface of the earth as a result of the freezing of precipitation particles (supercooled drizzle, supercooled rain, freezing rain, ice pellets, sometimes rain and snow) upon contact with a surface having a negative temperature. It is observed at air temperatures most often from zero to −10° (sometimes up to −15°), and during sudden warming (when the earth and objects still maintain a negative temperature) - at an air temperature of 0…+3°. It greatly impedes the movement of people, animals, and vehicles, and can lead to broken wires and breaking off tree branches (and sometimes to massive falls of trees and power line masts). The growth of ice continues as long as the supercooled precipitation lasts (usually several hours, and sometimes with drizzle and fog - several days). The deposited ice may persist for several days.

Black ice- a layer of lumpy ice or icy snow that forms on the surface of the earth due to the freezing of melt water when, after a thaw, the air and soil temperatures decrease (transition to negative temperature values). Unlike ice, black ice is observed only on the earth's surface, most often on roads, sidewalks and paths. The resulting ice can persist for many days in a row until it is covered with freshly fallen snow or melts completely as a result of an intense increase in air and soil temperatures.

First of all, let us define the very concept of “atmospheric precipitation”. In the Meteorological Dictionary, this term is interpreted as follows: “Precipitation is water in a liquid or solid state that falls from clouds or settles from the air on the surface of the earth and on objects.”

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

Each type of precipitation has its own characteristics.

Dew represents tiny 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 of crystalline ice, the particles of which are shaped like snowflakes.

frost- 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 subzero temperatures (below - 15°C). Frost can be crystalline and granular. On vertical objects, frost is deposited mainly on the windward side.

Among the precipitation deposited on the earth's surface, of particular importance is black 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 air temperatures from 0 to -3°C due to the freezing of drops of supercooled rain, drizzle or fog. A crust of frozen ice can reach a thickness of several centimeters and cause branches to break off.

Precipitation falling from clouds is divided into drizzle, heavy and shower.

Drizzle (drizzle) consist of very small drops of water with a diameter of less than 0.5 mm. They are characterized by low intensity. This precipitation usually falls from stratus and stratocumulus clouds. The speed at which the droplets fall is so slow that they appear to be suspended in the air.

Cover precipitation- this is rain consisting of small drops of water, or snowfall of snowflakes with a diameter of 1-2 mm. This is long-term precipitation that falls from dense altostratus and nimbostratus clouds. They can continue for several hours and even days, covering vast areas.

Rainfall characterized by high intensity. This is large-droplet and uneven precipitation that falls in both liquid and solid form (snow, pellets, hail, sleet). The downpour can last from a few minutes to several hours. The area covered by a rainstorm is usually small.

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

Precipitation is measured by the thickness of the water layer in millimeters. If 10 mm of precipitation fell, this means that the layer of water that fell on the surface of the earth is equal to 10 mm. What does 10 mm of precipitation mean for an area of ​​600 m2? It's not hard to calculate. Let's start the calculation for an area equal to 1 m2. For her, this amount of precipitation will be 10,000 cm 3, i.e. 10 liters of water. And this is a whole bucket. This means that for an area of ​​100 m2, 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.

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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 area, to buildings and structures and determining their thermal balance and the regime of natural illumination of the 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, loss solid precipitation from cloudiness determines snow loads 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 there are conventionally three tiers of clouds: 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 little shade the sunlight. In the middle tier there are altocumulus(drip) and high-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 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. 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 in high latitudes (especially in the Southern Hemisphere), with decreasing latitude it increases and reaches a maximum (about 7 points) in the belt from 60 to 70°, then towards the tropics cloudiness decreases to 2-4 points and increases again approaching the equator.

In Fig. 1.47 shows the overall cloudiness score on average per 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). The marine type is 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 of the 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 upward currents of 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. Minimum noted annual quantity precipitation - 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 with different temperatures and other physical properties meet. 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 side 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 o'clock 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. Determination of the amount of liquid precipitation is carried out using a measuring cup, and solid precipitation - using scales.

For automatic recording of the amount and intensity of liquid precipitation, 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. From the figure it follows that on the territory of the Russian Plain greatest number precipitation (600-700 mm/year) falls in the band 50-65° N. 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 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 the marginal seas of the Pacific Ocean, the number

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, and this amount falls in three days. winter months. The same amount of precipitation, but distributed evenly throughout the year, determines the existence of the zone mixed forests temperate latitudes. Many hydrological processes are also related to 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; V 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 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 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.

TO annual progress people are forced to adapt 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, the average duration of 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 by 10% more than in the nearby 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 when the air temperature is above 0 ° C, clear skies 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. Heavy 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 heat sources. 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, appearance which are 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 freezing, thinning and death of plants present in the urban greening system, and degradation natural complexes, part of 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 of irregular shape of 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 during the passage of 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 of splashes and dust can rise from the earth's surface, 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.

Discussed above dangerous phenomena 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 when gradients in the field increase atmospheric pressure and during the passage of fronts.

Weather stations monitor the duration of snowstorms and the number of days with snowstorms for individual months and winter period generally. 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 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 human body mainly characterized by beneficial effects. 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. Particular attention is paid to precipitation when choosing the design of walls, roofs and building foundations, and selecting building and roofing materials.

The impact of atmospheric precipitation on buildings is the moistening of the roof and external fences, leading to a change in their mechanical and thermophysical properties and affecting their service life, as well as the mechanical load on building structures created by solid precipitation 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.

Terms of accumulation for 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 some areas of the southern part of Kamchatka, the average height of snow cover can exceed 2 m. The depth 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 are complex 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 when planning populated areas for the most rational placement of residential and industrial buildings, and when developing measures to clear cities from snow.

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 a three-story building is placed inside the block 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. total area zones of snow transfer and blowing are 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 time becomes significantly 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 from 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 surfaces 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 C, 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 the 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 such a slope are widely used in the traditional architecture of northern countries, in mountainous regions and in 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 magnitude of the ice load on them depends on climatic conditions and on the technical parameters of 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 yield of orchards decreases, productivity decreases Agriculture. The formation of ice and black ice on roads creates hazardous 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 measures, such as electrical heating of the eaves, installation of shockers to release 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.

Precipitation- water in a liquid or solid state that falls from clouds or settles from the air onto the earth's surface.

Rain

Under certain conditions, cloud droplets begin to merge into larger and heavier ones. They can no longer stay in the atmosphere and fall to the ground in the form rain.

hail

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

Rice. 1. Origin of the hail

Snow

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

Dew and frost

Precipitation falling onto 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 precipitation gauge or rain gauge (Fig. 2).

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

Classification and types of precipitation

Precipitation is classified according to the nature of its occurrence, its origin, physical condition, fall seasons, etc. (Fig. 3).

According to the nature of precipitation, precipitation can be torrential, heavy and drizzling. Rainfall - intense, short-lived, cover a small area. Cover precipitation - medium intensity, uniform, long-term (can last for days, capturing large areas). Drizzle - fine precipitation falling over a small area.

Precipitation is classified according to its 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 the warmer air. Characteristic 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 high absolute and relative humidity.

Rice. 3. Types of precipitation

Comparing to climate map the annual amount of precipitation in the Amazonian lowland and the Sahara Desert, one can be convinced of its uneven distribution (Fig. 4). What explains this?

Precipitation comes from moist air masses that form over the ocean. This is clearly seen in areas with a monsoon climate. The summer monsoon brings a lot of moisture from the ocean. And there are continuous rains over the land, as on the Pacific coast of Eurasia.

Constant winds also play a big role in the distribution of precipitation. Thus, trade winds blowing from the continent bring dry air to northern Africa, where the largest desert in the world is located - the Sahara. Western winds bring rain from the Atlantic Ocean to Europe.

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

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

Relief also affects the distribution of precipitation, for example, the Himalayan mountains do not allow moist winds blowing from the north to pass through. Indian Ocean. Therefore, on their southern slopes sometimes up to 20,000 mm of precipitation falls per year. Moist air masses, rising along the mountain slopes (ascending air currents), cool, become saturated, and precipitation falls from 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 belts and precipitation. At the equator - in a low pressure zone - there is constantly heated air; rising upward, it cools and becomes saturated. Therefore, in the equator region there are many clouds and heavy rainfall. A lot of precipitation also falls in other areas of the globe where low pressure prevails. Wherein great importance has an air temperature: the lower it is, the less precipitation falls.

In high pressure belts, downward air currents predominate. As the air descends, it heats up and loses the properties of its saturation state. Therefore, at latitudes 25-30° precipitation occurs rarely and in small quantities. Areas of high pressure near the poles also receive little precipitation.

Absolute maximum precipitation registered on o. Hawaii ( Pacific Ocean) - 11,684 mm/year and in Cherrapunji (India) - 11,600 mm/year. The absolute minimum - in the Atacama Desert and the Libyan Desert - less than 50 mm/year; Sometimes there is no precipitation at all for years.

The moisture content of the area is characterized by humidification coefficient— the ratio of annual precipitation and evaporation for the same period. The humidification coefficient is denoted by the letter K, the annual precipitation by the letter O, and evaporation by the letter I; then K = O: I.

The lower the humidification coefficient, the drier the climate. If the annual precipitation is approximately equal to evaporation, then the humidification coefficient is close to unity. In this case, hydration is considered sufficient. If the moisture index is greater than one, then the moisture excessive, less than one - insufficient. When the humidification coefficient is less than 0.3, humidification is considered meager. Zones with sufficient moisture include forest-steppes and steppes, and zones with insufficient moisture include deserts.