Usually, natural resources are understood only as minerals extracted from the depths of the Earth. However, in recent years, scientists have begun to pay much attention to the “richness of the atmosphere,” namely rain and snow. Increasingly, reports of water shortages are coming from different parts of the world. This phenomenon is especially common in arid and semi-arid regions. Unfortunately, it is not limited only to these places. Due to the increase in the world's population, irrigation is more widely used in agriculture, and industry is growing, spreading throughout the globe. And this increases the need for fresh water every year. In a number of areas, the lack of cheap water is the most important factor limiting economic growth.

Currently, there are only two main sources of fresh water: 1) accumulated water in lakes and underground layers, 2) water in the atmosphere in the form of rain and snow.

Recently, great efforts have been made to develop means of desalinating water in the oceans. However, water obtained in this way is still too expensive to be used for agricultural and industrial purposes.

The waters of the lakes are of great importance for nearby settlements. But if the lakes are several hundred kilometers away from populated areas, their significance is almost completely lost, since laying pipes, installing and operating pumps makes the cost of delivered water too expensive. It may be surprising that during periods of prolonged hot weather with little rainfall, some Chicago suburbs experience severe water shortages despite being less than 80 km from one of the greatest reservoirs of fresh water - Lake Michigan.

In some areas, such as southern Arizona, a large share of the water used for irrigation and urban use comes from underground aquifers. Unfortunately, the aquifers are recharged very little by infiltrating rainwater. The water that is currently being extracted from underground is of very ancient origin: it has remained there since the time of glaciation. The amount of such water, called relict water, is limited. Naturally, with intensive water extraction using pumps, its level decreases all the time. There is no doubt that the total amount of underground water is quite large. However, the greater the depth from which water is extracted, the more expensive it is. Therefore, for some areas, other, more cost-effective sources of fresh water must be found.

One such source is the atmosphere. Due to evaporation from the seas and oceans, there is a large amount of moisture in the atmosphere. As is often said, the atmosphere is an ocean with low density water. If we take a column of air extending from the surface of the earth to a height of 10 km, and condense all the water vapor contained in it, then the thickness of the resulting water layer will range from a few tenths of a centimeter to 5 cm. The smallest layer of water gives cold and dry air, the largest - warm and humid. For example, in southern Arizona in July and August, the thickness of the layer of water contained in the atmospheric column averages more than 2.5 cm. At first glance, this amount of water seems small. However, if you take into account the total area occupied by the state of Arizona, you get a very impressive figure. It should also be noted that the reserves of this water are practically inexhaustible, since during windy times the air in Arizona is constantly saturated with moisture.

Naturally, a vital question arises: how much water vapor can fall as rain or snow in a given area? Meteorologists formulate this question somewhat differently. They ask how efficient rainmaking processes are in the area. In other words, what percentage of the water above a given surface in the form of vapor will actually reach the ground? The efficiency of rain formation processes varies in different parts of the globe.

In cold and humid areas, such as the Alaska Peninsula, efficiency is close to 100%. On the other hand, for dry areas like Arizona, the efficiency during the summer rainy season is only about 5%. If efficiency could be increased by even a very small amount, say to 6%, rainfall would increase by 20%. Unfortunately, we don't yet know how to achieve this. This task is the problem of transforming nature, which scientists around the world have been trying to solve for many years. Attempts at active interventions to stimulate rain formation processes began as early as 1946, when Langmuir and Schaefer showed that it was possible to artificially induce precipitation from certain types of clouds by seeding them with dry ice nuclei. Since then, certain progress has been made in methods of influencing clouds. However, there is not yet sufficient evidence to believe that the amount of precipitation from any cloud system can be artificially increased.

The main reason why meteorologists currently cannot change the weather is due to insufficient knowledge of the processes of precipitation formation. Unfortunately, we still do not always know the nature of rain formation in various cases.

SUMMER SHOWERS AND THUNDERSTORMS

Not so long ago, meteorologists believed that all precipitation was formed in the form of solid particles. When ice crystals or snowflakes enter warm air near the surface of the earth, they melt and turn into raindrops. This idea was based on the fundamental work of Bergeron, published by him in the early 30s. At the moment we are confident that the process of precipitation formation described by Bergeron does occur in most cases, but is not the only possible one.

However, another process is also possible, known as coagulation. In this process, raindrops grow by colliding and merging with smaller cloud particles. For rain to form by coagulation, the presence of ice crystals is no longer necessary. On the contrary, in this case there should be large particles that fall faster than the others and produce many collisions.

Radar played an important role in confirming the fact that the process of coagulation in clouds of convective development proceeds very efficiently. Convective clouds that resemble cauliflower sometimes develop into thunderstorms. Using radars with vertically scanning antennas, it is possible to observe the process of development of such clouds and note at what altitudes the first precipitation particles appear.

Studying the growth of a region of large particles up and down can only be done by continuously observing the same cloud. Using this method, a series of observations were obtained, one of which is shown in Fig. 20. The series consists of 11 different radar observations, illustrated with photograms at intervals of 10 to 80 seconds.

As can be seen from the figure shown. 20 series of observations, the primary radio echo extended to an altitude of about 3000 m, where the temperature was 10° C. Then the radio echo quickly developed both up and down. However, even when it reached its maximum size, its peak did not exceed 6000 m, where the temperature was about 0°C. Obviously, there is no reason to believe that the rain in this cloud could have formed from ice crystals, since the precipitation zone arose in the region of positive temperatures.

A large number of similar radar observations were made in different areas of the USA, Australia and England. Such observations suggest that the coagulation process plays a major role in the formation of storm precipitation. The question arises why this important fact was not established before the use of radar. One from The main reasons explaining this circumstance is that it is impossible to determine where and when the first precipitation particles appear in the cloud. It should be noted that when rain falls, the top of the cloud can extend to a height of several thousand meters, reaching an area with temperatures of -15 ° C and below, where many ice crystals exist. This circumstance previously led to the erroneous conclusion that ice crystals are sources of precipitation.

At present, unfortunately, we do not yet know the relative role of both mechanisms of rain formation. A more detailed study of this issue will help meteorologists more successfully develop methods of artificial influence on clouds.

SOME PROPERTIES OF CONVECTIVE CLOUDS

Radar observations have made it possible to study convective clouds in more detail. Using different types of radar, researchers have found that in some cases individual radio echo "towers" develop to very high altitudes. So, for example, in some cases clouds having a diameter of 2-3 km, extends until 12-13 km.

Severe thunderstorms usually develop in stages. Initially, one of the radio echo towers grows, reaching a height of about 8000 m, then decreases. A few minutes later, next to this tower, another begins to stretch upward, which reaches a greater height - about 12 km. The stepwise growth of the radio echo continues until the thundercloud reaches the stratosphere.

Thus, each radio echo tower can be considered as a separate brick in a general building or as a single cell of the entire system - a thundercloud. The existence of such cells in a thundercloud was postulated at one time by Byers and Braham based on the results of an analysis of a large number of meteorological observations carried out on various characteristics of thunderstorms. Byers and Braham suggested that a thundercloud consists of one or more such cells, the life cycle of which is very short. At the same time, a group of English researchers led by Scorer and Ludlam put forward their theory of thunderstorm formation. They believed that in every thundercloud there were large bubbles of air rising from the ground to the upper layers. Despite the differences in theories of thunderstorm formation, both of these theories still assume that the development of a thunderstorm cloud occurs in steps.

Studies have shown that the average growth rates of radio echo towers in convective clouds range from 5 to 10 m/sec, and in some types of thunderclouds they can be two to three times larger. It is clear that in this case, aircraft entering such clouds experience significant bumps and overloads under the influence of strong updrafts and intense turbulence.

Anyone who has waited out a thunderstorm knows that it can last an hour or more. At the same time, the life of an individual turret or cell is very short: as radar observations show, approximately 23 minutes. Obviously, in a large thundercloud there can be many cells developing sequentially one after another. In this case, from the moment the rain appears until it stops, much more time may pass than 23 minutes. During a thunderstorm, which can last for several hours, the intensity of rain does not remain constant. On the contrary, it either reaches a maximum or decreases until the rain almost completely disappears. Each such increase in rain intensity corresponds to the development of another cell or tower. It is not difficult to verify the above for yourself if you watch, with a watch in your hands, the alternation of maximums and minimums of the intensity of heavy rain.

WINTER PRECIPITATION

During the warm season, a significant portion of precipitation falls from showers and thunderclouds. Individual clouds extending to high altitudes produce precipitation in the form of localized showers. The coagulation process plays an important role in the formation of precipitation from such clouds. As a rule, individual clouds have small cross-sectional areas, powerful ascending and descending currents develop in them, and their duration of existence is no more than an hour.

Most of the precipitation that falls in. the cold season gives clouds of a different type. Instead of local clouds in winter, cloud systems appear spreading over a huge area, existing not for hours, but for days. Such cloud systems are formed due to very slow vertical movement of air (at a speed of less than 1 m/sec, in some cases even 10 cm/sec.).

The clouds from which most of the precipitation falls are called nimbostratus. Their shape is determined by slow but prolonged upward movements of air in cyclones that arise in mid-latitudes and move with westerly currents. Rainfall from such cloud systems is commonly referred to as heavy rainfall. They are more uniform in structure than rain from convective clouds. However, when observing such systems with radar, areas of higher precipitation intensity are found within areas where precipitation would be expected to be uniformly distributed. Such areas are observed where the velocities of updrafts are noticeably higher than the average values.

In Fig. Figure 21 shows a photogram of a typical radar pattern of winter precipitation. The photogram was obtained at McGill University (Canada) using a radar with a fixed vertical antenna. This observation method provided a cross-section of the entire cloud system that passed over the station. The above photogram was obtained by exposing the film, moving slowly in front of the all-round indicator screen, on which only a vertical scan line with brightness varying in height was visible in those places where a radio echo was noted. Thus, the resulting radio echo pattern in a photogram can be considered as a sum of instantaneous patterns consisting of many closely spaced vertical lines.

In the photogram you can see that at an altitude of more than 2500 m oblique streamers are observed, turning into vertical and regularly located bright cells. A team of researchers from McGill University, led by Marshall, suggested that the bright cells represent areas in which ice crystals form, and the inclined streamers represent bands of falling precipitation.

If the wind speed does not change with height, then the speed of falling precipitation particles is also constant. In this case, it is not difficult to derive a simple relation describing the trajectory of falling particles. To calculate particle fall rates, Marshall used an observational method of recording a radio echo pattern on a slowly moving film. Having analyzed one of the most clearly recorded cases and determined that the average particle falling speed was about 1.3 m/sec, Marshall suggested that the particles were conglomerates of ice crystals.

When examining a bright line of radio echo (in the photogram this is a band at an altitude of about 2000 m) it becomes obvious that the nucleated sediment particles, at least for the most part, are solid. The bright band appears slightly below the melting level, near the 0°C isotherm. The phenomenon of a bright radio echo band in photograms of winter precipitation has been noted by many researchers and has been studied in detail recently.

The first to give a satisfactory explanation for this phenomenon was Ride. His hypothesis, developed in 1946, is still considered correct; Later, other researchers made some clarifications to it.

Ride was the first to show that when the size of reflecting particles is much smaller than the wavelength, their reflectivity in the liquid state is approximately five times higher than in the solid state. A sharp increase in radio echo intensity below the zero isotherm level occurs due to the rapid melting of falling solid particles. Once melted, the particles quickly turn into spherical water droplets that fall faster than snowflakes. An increase in the rate of falling of particles below the 0°C isotherm and the associated decrease in their number per unit volume of air, and consequently, inside the volume illuminated by the radar beam, lead to a decrease in the intensity of the radio echo below the melting layer. In Fig. 21 it can be seen that the radio echo stripes located below the bright line are somewhat steeper than the radio echo stripes located above it. The greater steepness of the fall bands in the region below the melting level indicates that particles fall faster here.

Based on the analysis of such observations, it can be concluded that the rain that falls from some forms of winter clouds occurs at very low temperatures. Even in completely isolated clouds, ice crystals form and can grow and increase in size until they fall out. When they collide, the crystals combine into snowflakes, which move along a trajectory determined by their falling speeds and the wind. Penetrating into the lower layers, snowflakes can enter clouds consisting of small supercooled drops and continue to grow due to collisions with them. Such clouds themselves cannot be detected by most modern radars due to the small size of the droplets. As soon as solid particles pass the zero isotherm level, they quickly melt and increase the speed of their fall. When such particles enter lower clouds, they continue to grow due to collisions and mergers with cloud drops. If the temperature at the earth's surface is below 0°C, precipitation particles will remain in the form of snowflakes.

However, not all widespread cloud systems exhibit distinct above-freezing streamers such as those shown in Fig. 22. In some cases, clouds create only distinct and bright bands of radio echo, above which there are no noticeable reflections. This pattern likely occurs because the ice crystals above the bright band are too small to produce a detectable radio echo. When such crystals enter the melting region, their reflectivity increases due to both a change in phase state and a further increase in their size due to merging with smaller droplets.

Radar observations led to a number of important conclusions. It has been firmly established that the rain that falls from most winter clouds and reaches the surface of the earth forms at high altitudes in the form of ice crystals. On the other hand, rainfall from convective clouds often occurs in the absence of ice crystals.

When researchers succeed in establishing the role of the solid phase and the coagulation process in the formation of precipitation from this type of cloud, there will be a real opportunity to actively influence them in order to artificially induce precipitation. There is no doubt that sooner or later a person will learn to control the clouds. Meteorologists around the world are joining forces to speed up this task. By learning to control the process of sedimentation, they will be able to contribute to solving the problem of the world's water resources. One can hope that when the possibility of artificially regulating precipitation becomes possible, means will be found to use it more effectively.

The upper layers of cumulonimbus and altostratus clouds, where temperatures are well below freezing, consist mainly of ice floes.

Since the temperature in the middle layers is slightly higher, ice crystals present in rising and falling air currents collide with super-cooled water droplets. When they come into contact, they form large crystals, heavy enough to tend downwards, despite the rising air currents.

As the crystals fall, they collide with other cloud particles and grow larger. If the temperature below is below freezing, they fall to the ground as snow. If there is warm air above the soil, they turn into raindrops. If the rising air currents inside the cloud are strong enough, the ice crystals can rise and fall several times, continuing to grow and eventually become very heavy and fall as hail. One of the largest hailstones ever recorded fell in Coffeyville (Kansas) in 1970. It was almost 15 cm wide and weighed 700 g.

Rain, snow or hail

Most of the cloud layers with the coldest temperatures (graph on the left) are ice particles. With slightly increased temperatures in the lower layers, ice mixes with water droplets and forms crystals large enough to fall as rain, snow or, under suitable conditions, hail.

Precipitation formation

This model of cumulonimbus formation (right) shows the path of air currents carrying warm, steam-laden air into cooler layers and returning as rain, snow or hail.

Long-term (from several hours to a day or more) precipitation in the form of rain (covered rain) or snow (covered snow), falling over a large area with a fairly uniform intensity from nimbostratus and altostratus clouds on a warm front. Continuous precipitation moisturizes the soil well.

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 forms when falling snowflakes hit a layer of warm air deep enough for the snowflakes to completely melt and become raindrops. As these droplets continue to fall, they pass through a thin layer of cold air above the earth's surface and their temperature drops below freezing. However, the droplets themselves do not freeze, so this phenomenon is called supercooling (or the formation of “supercooled droplets”).

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. They are formed when raindrops freeze as they fall through the lower layer of air with a negative temperature. 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

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.

Fog- an accumulation of condensation products (droplets or crystals, or both) suspended in the air directly above the surface of the earth. Cloudiness of the air caused by such accumulation. Usually these two meanings of the word fog are not distinguished. In fog, horizontal visibility is less than 1 km. Otherwise, the cloudiness is called haze.

Rainfall

Shower- short-term precipitation, usually in the form of rain (sometimes wet snow, cereals), characterized by high intensity (up to 100 mm/h). Occurs in unstable air masses on a cold front or as a result of convection. Typically, torrential rain covers a relatively small area.

Rain shower- 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 of various shapes and sizes: usually the diameter of hailstones is 2-5 mm, but in some cases individual hailstones reach the size of a pigeon and even a chicken egg ( then 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.

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.

Any schoolchild knows these days, but it’s still worth brushing up on your knowledge. Water vapor is an invisible but always present component of the air surrounding the Earth. In all bodies of water on earth, from oceans and seas to small ponds, the process of water evaporation constantly occurs. It changes from liquid to gaseous vapor. The warmer the water, the faster it evaporates, and the larger the area of ​​the reservoir, the more water turns into steam. People do not see this evaporation; water vapor becomes visible where it cools, where condensation occurs, that is, at high altitudes. Condensation is the process of converting invisible vapor into a visible liquid. Solar energy plays a major role in this. It lifts steam high into the sky and turns into clouds. The wind, in turn, carries it over long distances, distributing vital moisture throughout the earth.

Mechanism of rain formation

How are raindrops formed? As soon as the cloud is completely saturated and cannot accept moisture, the process of falling of the smallest droplets begins inside it. As they fall, they bind with other droplets, which create even larger droplets, and as a result, rain can be observed to form.

During a downpour, large droplets are created that can reach 7 mm in diameter. A drop of light rain less than half a millimeter. During light rain, the drops practically do not separate into separate ones, and everything becomes wet. Rain is actually a cloud that sheds itself. This is observed when the drops or crystals from which it is created become too heavy and fall towards the Earth. Meteorologists identify several methods for turning droplets into rain. How rain forms depends on whether the clouds the droplets pass through are warm or cold. Warm clouds are made from tiny particles of water. Falling drops often turn into steam as they fly to the ground. And sometimes they are so big that they fall to the ground in the form of a shower. A tiny droplet passes through a cloud, at the same time it collides with other droplets, and, having already united, they create a large droplet. Such a drop collects other drops on its way down. The air that rushes around the high-speed droplet attracts tiny droplets, increasing its weight. Sometimes she becomes so heavy that she falls from a height into a puddle.

Where do snowflakes come from?

Rain, snow - all these phenomena are studied by meteorologists and weather forecasters in order to anticipate them and warn the population about bad weather in time. In cold clouds, droplets form as ice crystals. Cold clouds form high in the sky and are transported to areas where temperatures are always above freezing (0°C). Such clouds are a mixture of water droplets and ice crystals. When water evaporates from liquid droplets, it adheres to the crystals, freezing and turning into a solid. As the crystals grow and take on moisture, they turn into snowflakes and fall through the cloud. But unless it's too cold outside, snowflakes don't last long. They descend into layers of warm air and begin to melt, turning back into raindrops. How do snowflakes appear? If a cloud contains zones of different temperatures and humidity, it turns into a snow machine. Moist warm air, which carries water droplets with it, passes into the dry, cold areas of the cloud. Due to the low temperature, the droplets freeze and form the core of the future snowflake. Particles of warm water gather around the core in a certain order, turning into a snow crystal. Each snowflake consists of 2-200 individual crystals. The crystals form in cold clouds high above the earth, where temperatures can drop to -40°C and water vapor freezes into ice. The snow crystal leaves the cloud and falls to the ground. Snow appears crystal clear when it falls, but in reality most snowflakes are created around tiny particles of dust that the wind has carried into the sky; water vapor can crystallize even around small particles of smoke. If you look at it through powerful microscopes, you can see these particles hiding inside snowflakes. Three-quarters of the snowflakes grew around tiny, invisible pieces of clay or soil.

Snowflakes shape

Probably, every person had the opportunity to admire the intricate shape of snowflakes when, smoothly falling from the sky, they settle on a mitten or coat. Each snowflake has a different shape and its own special structure. The basic shape of a snow crystal depends on the temperature at which the snowflake formed. The higher the cloud is, the colder it is. From high temperatures in which the temperature is below -35 o C, hexagonal prisms are created, when the temperature of the clouds is in the range of -3-0 o C, snowflakes in the form of plates are formed. At a temperature of -5-3 o C, needle-shaped snowflakes are formed, and from -8-5۫ o C in the form of columns. At -12-8 o C, plates form again. If the temperature drops below, snowflakes take on the shape of stars. As snowflakes grow larger, they become heavier and fall towards the ground, their shape changing. If snowflakes fall while rotating, their shape will be perfectly symmetrical; if they fall, swaying to the sides, their shape will become irregular.

If the air under a snow cloud is warmer than 0 o C, snowflakes can melt as they fall, turning into raindrops, this explains how rain and snow turning into rain are formed. But if the air is cold enough, snowflakes will fly to the ground, covering it with a white blanket. Once on the ground, the snow crystals gradually lose their subtle patterns, being compressed under the influence of other snowflakes.

When does frost fall?

Frost refers to solid atmospheric precipitation that falls in a thin layer of ice crystals. Appears on the ground and objects when the soil is freezing, there is a calm wind and a clear sky. At temperatures below zero it precipitates in the form of hexagonal crystals, at lower temperatures - in the form of plates, below -15 ° C frost crystals take the form of blunt needles. Frost forms on any objects whose surface is colder than the air: on grass, ground, roofs, glass.

Acid rain

(rain, snow) with a high acid content represent How are they formed? The sources of acid rain can be both natural processes (volcanic activity, decomposition of plant residues) and industrial emissions, primarily sulfur dioxide (SO 2) and nitrogen oxides (NO, NO 2, N 2 O 3), when burning various types of fuel. Combining with moisture in the atmosphere, they form sulfuric and nitric acids. If acidic substances, having dissolved in the air, enter an atmosphere saturated with moisture, then the acids fall on the ground. If water, including acids, falls on vegetation and the ground, it harms the flora and fauna of the earth.

Colorful rains

Sometimes people can observe phenomena such as colored rain. Colored rain is rare, but it can actually be colored. How is rain with different colors formed? For example, red rain was seen in April 1970 in Thessaloniki, Greece. A powerful wind over the Sahara Desert lifted many particles of red clay high into the sky, and then transferred them to the clouds in the sky over Greece. A stream of rain washed away the clay from the clouds, but the color of the rain was red for some time. In 1959, yellow-green rain fell in Massachusetts. The culprit turned out to be spring pollen from plants, raised high. And back in March 1972, blue snow fell in the French Alps: this snow was colored by minerals brought from the Sahara.

RAIN
water formed by the condensation of water vapor that falls from clouds and reaches the earth's surface in the form of liquid droplets. The diameter of raindrops ranges from 0.5 to 6 mm. Drops smaller than 0.5 mm are called drizzle. Drops larger than 6 mm are highly deformed and break when falling to the ground. Depending on the volume of precipitation falling over a certain period of time, light, moderate and heavy (storm) rains are distinguished by intensity. The intensity of light rain varies from negligible to 2.5 mm/h, moderate rain - from 2.8 to 8 mm/h and heavy rain - more than 8 mm/h, or more than 0.8 mm in 6 minutes. Covering, prolonged rains with continuous clouds over a large area are usually weak and consist of small drops. Rainfall that occurs sporadically over small areas is usually more intense and consists of larger droplets. In one strong thunderstorm lasting only 20-30 minutes, up to 25 mm of precipitation can fall.
Water cycle (moisture cycle). Water evaporates from the surface of oceans, rivers, lakes, swamps, soil, and plants (as a result of transpiration). It accumulates in the atmosphere in the form of invisible water vapor. The rate of evaporation and transpiration is determined mainly by temperature, air humidity and wind strength and therefore varies greatly from place to place and depending on meteorological conditions. Most atmospheric water vapor comes from warm tropical and subtropical seas and oceans. The average evaporation rate for the entire globe is approx. 2.5 mm per day. In general, it is balanced by the average global amount of precipitation (approx. 914 mm/year). The total supply of water vapor in the atmosphere is equivalent to approximately 25 mm of precipitation, so on average it is renewed every 10 days. Water vapor is carried upward and distributed in the atmosphere by air currents of various sizes - from local convective currents to global wind systems (westerly transport or trade winds). As warm, moist air rises, it expands due to the decrease in pressure in the high atmosphere and cools. As a result, the relative humidity of the air increases until the air reaches a state of saturation with water vapor. Its further rise and cooling lead to the condensation of excess moisture on the smallest particles suspended in the air and to the formation of clouds consisting of water droplets. Inside the clouds, these droplets are only approx. 0.1 mm fall very slowly, but they are not all the same size. Larger drops fall faster, overtaking smaller ones encountered on their way, collide and merge with them. Thus, larger droplets grow due to the addition of smaller ones. If a drop in a cloud travels a distance of approx. 1 km, it can become quite heavy and fall out like a raindrop. Rain can form in other ways. Droplets at the top, cold part of the cloud can remain liquid even at temperatures well below 0°C, the normal freezing point of water. Such drops of water, called supercooled drops, can freeze only if special particles called ice nuclei are embedded in them. Frozen droplets grow into ice crystals, and several ice crystals can combine to form a snowflake. Snowflakes pass through a cloud and, in cold weather, reach the ground as snow. However, in warm weather they melt and reach the surface in the form of raindrops.

The amount of precipitation reaching the surface of the earth in a given place in the form of rain, hail or snow is estimated by the thickness of the water layer (in millimeters). It is measured by special instruments - precipitation gauges, which are usually located at a distance of several kilometers from one another and record the amount of precipitation over a certain period of time, usually 24 hours. A simple precipitation gauge consists of a vertically mounted cylinder with a round funnel. Rainwater enters the funnel and flows into a graduated measuring cylinder. The area of ​​the measuring cylinder is 10 times smaller than the area of ​​the funnel inlet, so that a layer of water 25 mm thick in the measuring cylinder corresponds to 2.5 mm of precipitation. More sophisticated measuring instruments continuously record the amount of precipitation on a tape mounted on a clock-driven drum. One of these devices is equipped with a small vessel that automatically tips over and releases water, and also closes an electrical contact when the amount of water in the rain gauge corresponds to a layer of precipitation of 0.25 mm. A fairly reliable assessment of rain intensity over a large area is provided by the use of the radar method. The average annual precipitation over the entire surface of the Earth is approx. 910 mm. In tropical regions, the average annual precipitation is at least 2500 mm, in temperate latitudes - approx. 900 mm, and in the polar regions - approx. 300 mm. The main reasons for differences in precipitation distribution are the geographical location of a given region, its altitude, distance from the ocean and the direction of prevailing winds. On mountain slopes facing the winds blowing from the ocean, the amount of precipitation is usually high, while in areas protected from the sea by high mountains, very little precipitation falls. The maximum annual rainfall (26,461 mm) was recorded in Cherrapunji (India) in 1860-1861, and the highest daily rainfall (1618.15 mm) was recorded in Baguio in the Philippines on July 14-15, 1911. The minimum rainfall was recorded in Arica (Chile), where the annual average over a 43-year period was only 0.5 mm, and in Iquique (Chile) not a single rain fell in 14 years.
Artificial rain. Because some clouds are thought to produce little or no precipitation due to a lack of condensation nuclei capable of initiating the growth of snow crystals or raindrops, attempts are being made to create "man-made rain." Deficiency of condensation nuclei can be compensated by dispersing substances such as dry ice (frozen carbon dioxide) or silver iodide. For this, dry ice pellets with a diameter of approx. 5 mm are thrown from an airplane onto the upper surface of a supercooled cloud. Each granule, before evaporating, cools the air around it and generates about a million ice crystals. It only takes a few kilograms of dry ice to seed a large rain cloud. Hundreds of experiments carried out in many countries have shown that seeding cumulus clouds with dry ice at a certain stage of their development can stimulate rain (and rain does not fall from neighboring clouds that have not undergone such treatment). However, the amount of "artificial" precipitation that falls is usually small. To increase the amount of precipitation over a large area, silver iodide vapor is sprayed from an airplane or from the ground. These particles are carried from the ground by air currents. In clouds, they can combine with supercooled water droplets and cause them to freeze and grow into snow crystals. There is still no truly convincing evidence that it is possible to achieve significant increases (or decreases) in precipitation over large areas. It may be possible in some cases to achieve small changes (5-10%), but usually they cannot be distinguished from natural interannual fluctuations.
LITERATURE
Drozdov O.A., Grigorieva A.S. Moisture circulation in the atmosphere. L., 1963 Khromov S.P., Petrosyants M.A. Meteorology and climatology. M., 1994

Collier's Encyclopedia. - Open Society. 2000 .

Antonyms:

See what "RAIN" is in other dictionaries:

rain- rain, I... Russian spelling dictionary

rain- rain/ … Morphemic-spelling dictionary

RAIN, rain, rain, rain, rain husband. water in drops or streams from clouds. (Ancient dezg; dezgem, rain; dezgevy, rain; dezgiti, rain). Sitnichek, the finest rain; downpour, torrential, the strongest; side-lash, undercut, oblique... ... Dahl's Explanatory Dictionary

- (rain, rain), downpour, downpour; slush; (simple) cottonweed, rubbish, braid. Mushroom rain, large, fine, continuous, torrential, tropical, frequent. It’s raining, drizzling, drizzling, pouring (it’s pouring, it’s pouring like buckets), it doesn’t stop... Synonym dictionary

Noun, m., used. often Morphology: (no) what? rain, why? rain, (see) what? rain, what? rain, what about? about rain; pl. What? rain, (no) what? rain, why? rain, (I see) what? rains, what? rains, about what? about rain 1. Rain is precipitation... Dmitriev's Explanatory Dictionary

I; m. 1. Atmospheric precipitation falling from clouds in the form of water drops. Warm summer village. Strong village. Prolivnoy village (very strong). Mushroom village (rain and sun, after which, according to popular belief, mushrooms grow abundantly). D. is coming. D. drizzling, pouring... ... encyclopedic Dictionary

- (1): Other days will soon tell the bloody dawns of the world; Black clouds are coming from the sea, wanting to cover the sun, and blue millions are trembling in them. There will be great thunder, it will rain like arrows from Don the Great. Hit this one with a spear, that one with a saber... ... Dictionary-reference book "The Tale of Igor's Campaign"

RAIN, rain (doš, dozhzha), husband. 1. A type of precipitation in the form of water droplets. Pouring rain. 2. transfer A stream of small particles falling in a multitude (book). Rain of sparks Star Rain. || trans. Multitude, continuous abundance (book).... ... Ushakov's Explanatory Dictionary