Interaction between the ocean and the atmosphere.

27. Circulation of air masses.

© Vladimir Kalanov,
"Knowledge is power".

The movement of air masses in the atmosphere is determined by thermal conditions and changes in air pressure. The set of main air currents over the planet is called general atmospheric circulation. The main large-scale atmospheric movements that make up the general circulation of the atmosphere: air currents, jet streams, air flows in cyclones and anticyclones, trade winds and monsoons.

Air movement relative earth's surface – wind- appears because atmospheric pressure in various places air mass is not the same. It is generally accepted that wind is the horizontal movement of air. In fact, the air usually moves not parallel to the surface of the Earth, but at a slight angle, because atmospheric pressure changes in both horizontal and vertical directions. Wind direction (north, south, etc.) means which way the wind is blowing. Wind force refers to its speed. The higher it is, the stronger the wind. Wind speed is measured at weather stations at an altitude of 10 meters above the Earth, in meters per second. In practice, wind strength is measured in points. Each point corresponds to two to three meters per second. With a wind force of 9, it is already considered a storm, and with a wind of 12, it is considered a hurricane. The common term "storm" means any very strong wind, regardless of the number of points. The speed of strong winds, for example, during a tropical hurricane, reaches enormous values ​​- up to 115 m/s or more. Wind increases on average with height. At the Earth's surface, its speed is reduced by friction. In winter, wind speeds are generally higher than in summer time. The highest wind speeds are observed in temperate and polar latitudes in the troposphere and lower stratosphere.

The pattern of changes in wind speed over continents at low altitudes (100–200 m) is not entirely clear. here wind speeds reach the highest large values in the afternoon, and the smallest ones at night. This is best observed in the summer.

Very strong winds, up to stormy winds, occur during the day in the deserts of Central Asia, and at night there is complete calm. But already at an altitude of 150–200 m, the exact opposite picture is observed: maximum speed at night and minimum during the day. The same picture is observed both in summer and winter in temperate latitudes.

Gusty winds can cause a lot of trouble for airplane and helicopter pilots. Jets of air moving in different directions, in shocks, gusts, sometimes weakening, sometimes intensifying, create a great obstacle to the movement of aircraft - bumpiness appears - a dangerous disruption to normal flight.

Winds blowing from the mountain ranges of the cooled continent towards warm sea, are called bora. This is a strong, cold, gusty wind that usually blows in the cold season.

Many people know the bora in the Novorossiysk region, on the Black Sea. These are created here natural conditions that the bora speed can reach 40 and even 60 m/s, and the air temperature drops to minus 20°C. Boron occurs most often between September and March, on average 45 days a year. Sometimes its consequences were as follows: the harbor froze, ice covered ships, buildings, the embankment, roofs were torn off houses, carriages overturned, ships were thrown ashore. Boron is also observed in other regions of Russia - on Lake Baikal, on Novaya Zemlya. Bora is known on the Mediterranean coast of France (where it is called mistral) and in the Gulf of Mexico.

Sometimes vertical vortices with rapid spiral-like air movement appear in the atmosphere. These whirlwinds are called tornadoes (in America they are called tornadoes). Tornadoes can be several tens of meters in diameter, sometimes up to 100–150 m. It is extremely difficult to measure the air speed inside a tornado. Based on the nature of the destruction produced by a tornado, the estimated speed values ​​may well be 50–100 m/s, and in particularly strong vortices – up to 200–250 m/s with a large vertical component of the speed. The pressure in the center of the rising tornado column drops by several tens of millibars. Millibars are usually used to determine pressure in synoptic practice (along with millimeters of mercury). To convert bars (millibars) to mm. There are special tables for the mercury column. In the SI system, atmospheric pressure is measured in hectopascals. 1gPa=10 2 Pa=1mb=10 -3 bar.

Tornadoes do not last long - from several minutes to several hours. But even in this short time they manage to cause a lot of trouble. When a tornado (over land, tornadoes are sometimes called blood clots) approaches buildings, the difference between the pressure inside the building and in the center of the blood clot leads to the fact that the buildings seem to explode from the inside - walls are destroyed, glass and frames fly out, roofs are torn off, and sometimes there are no casualties involved. victims. There are cases when people, animals, as well as various items a tornado lifts into the air and carries it tens or even hundreds of meters. In their movement, tornadoes move several tens of kilometers over the sea and even more over land. The destructive power of tornadoes over the sea is less than over land. In Europe, blood clots are rare; they occur more often in the Asian part of Russia. But tornadoes are especially frequent and destructive in the United States. Read more about tornadoes and tornadoes on our website in the section.

Atmospheric pressure is very variable. It depends on the height of the air column, its density and the acceleration of gravity, which varies depending on the latitude and altitude above sea level. The density of air is the mass per unit volume. The density of wet and dry air differs noticeably only at high temperatures and high humidity. As the temperature decreases, the density increases; with altitude, the air density decreases more slowly than the pressure. Air density is usually not measured directly, but is calculated using equations based on measured temperatures and pressures. Air density is indirectly measured by the deceleration of artificial Earth satellites, as well as from observations of the spreading of artificial clouds of sodium vapor created by weather rockets.

In Europe, the air density at the Earth's surface is 1.258 kg/m3, at an altitude of 5 km - 0.735, at an altitude of 20 km - 0.087, and at an altitude of 40 km - 0.004 kg/m3.

The shorter the air column, i.e. the higher the place, the less pressure. But the decrease in air density with height complicates this relationship. The equation expressing the law of pressure change with height in a resting atmosphere is called the basic equation of statics. It follows from it that with increasing altitude the change in pressure is negative, and when rising to the same height, the greater the pressure drop, the greater the air density and the acceleration of gravity. The main role here belongs to changes in air density. From the basic equation of statics, one can calculate the value of the vertical pressure gradient, which shows the change in pressure when moving per unit height, i.e. decrease in pressure per unit vertical distance (mb/100 m). The pressure gradient is the force that moves air. In addition to the force of the pressure gradient in the atmosphere, inertial forces (Coriolis and centrifugal forces), as well as frictional forces, act. All air currents are considered relative to the Earth, which rotates around its axis.

The spatial distribution of atmospheric pressure is called the pressure field. This is a system of surfaces of equal pressure, or isobaric surfaces.

Vertical section of isobaric surfaces above the cyclone (H) and anticyclone (B).
Surfaces drawn through equal intervals pressure p.

Isobaric surfaces cannot be parallel to each other and to the earth's surface, because temperature and pressure constantly change in the horizontal direction. Therefore, isobaric surfaces have a varied appearance - from shallow “basins” bent downwards to stretched “hills” bent upwards.

When a horizontal plane intersects isobaric surfaces, curves are obtained - isobars, i.e. lines connecting points with the same pressure values.

Isobar maps, which are constructed based on the results of observations at a certain point in time, are called synoptic maps. Isobar maps compiled from average long-term data for a month, season, year are called climatological.

Long-term average maps of the absolute topography of the isobaric surface 500 mb for December - February.
Heights in geopotential decameters.

On synoptic maps, an interval of 5 hectopascals (hPa) is adopted between isobars.

On maps of a limited area, isobars may break off, but on a map of the entire globe, each isobar is naturally closed.

But even on a limited map there are often closed isobars that limit areas of low or high pressure. Areas of low pressure in the center are cyclones, and areas with relatively high pressure are anticyclones.

By cyclone we mean a huge vortex in the lower layer of the atmosphere, with low atmospheric pressure in the center and upward movement of air masses. In a cyclone, pressure increases from the center to the periphery, and the air moves counterclockwise in the Northern Hemisphere and clockwise in Southern Hemisphere. The upward movement of air leads to the formation of clouds and precipitation. From space, cyclones appear as swirling cloud spirals in temperate latitudes.

Anticyclone- This is an area of ​​high pressure. It arises simultaneously with the development of a cyclone and is a vortex with closed isobars and the highest pressure in the center. Winds in an anticyclone blow clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. In an anticyclone, there is always a downward movement of air, which prevents the occurrence of heavy clouds and prolonged precipitation.

Thus, large-scale atmospheric circulation in temperate latitudes constantly reduces to the formation, development, movement, and then to the attenuation and disappearance of cyclones and anticyclones. Cyclones that arise at the front separating warm and cold air masses move towards the poles, i.e. carry warm air to polar latitudes. On the contrary, anticyclones that arise in the rear of cyclones in a cold air mass move to subtropical latitudes, carrying cold air there.

An average of 75 cyclones occur over the European territory of Russia per year. The diameter of the cyclone reaches 1000 km or more. In Europe, there are an average of 36 anticyclones per year, some of which have a central pressure of more than 1050 hPa. The average pressure at sea level in the Northern Hemisphere is 1013.7 hPa, and in the Southern Hemisphere it is 1011.7 hPa.

In January in the northern parts of the Atlantic and Pacific Ocean areas observed low pressure, named Icelandic And Aleutian depressions. Depression, or baric minimums, are characterized by minimal pressure values ​​- on average about 995 hPa.

During the same period of the year, areas of high pressure arise over Canada and Asia, called the Canadian and Siberian anticyclones. The highest pressure (1075–1085 hPa) is recorded in Yakutia and the Krasnoyarsk Territory, and the minimum is in typhoons over the Pacific Ocean (880–875 hPa).

Depressions are observed in areas where cyclones often occur, which, as they move east and northeast, gradually fill and give way to anticyclones. The Asian and Canadian anticyclones arise due to the presence of the vast continents of Eurasia and North America at these latitudes. In these areas, anticyclones dominate over cyclones in winter.

In summer, over these continents, the pattern of pressure field and circulation changes radically, and the zone of cyclone formation in the Northern Hemisphere shifts to higher latitudes.

In the temperate latitudes of the Southern Hemisphere, cyclones that arise over the homogeneous surface of the oceans, moving to the southeast, encounter the ice of Antarctica and stagnate here, having low air pressure at their centers. In winter and summer, Antarctica is surrounded by a belt of low pressure (985–990 hPa).

In subtropical latitudes, atmospheric circulation is different over the oceans and in areas where continents and oceans meet. There are areas of high pressure over the Atlantic and Pacific oceans in the subtropics of both hemispheres: these are the Azores and South Atlantic subtropical anticyclones (or pressure lows) in the Atlantic and the Hawaiian and South Pacific subtropical anticyclones in the Pacific Ocean.

The equatorial region constantly receives the greatest amount of solar heat. Therefore, in equatorial latitudes (up to 10° northern and southern latitude along the equator), low atmospheric pressure is maintained throughout the year, and in tropical latitudes, in the band 30–40° N. and S. – increased, resulting in the formation of constant air currents directed from the tropics to the equator. These air currents are called trade winds. Trade winds blow throughout the year, changing their intensity only within minor limits. These are the most stable winds on the globe. The force of the horizontal pressure gradient directs air flows from areas high blood pressure to the area of ​​low pressure in the meridional direction, i.e. to the south and north. Note: the horizontal pressure gradient is the pressure difference per unit distance normal to the isobar.

But the meridional direction of the trade winds changes under the influence of two inertial forces - the deflecting force of the Earth's rotation (Coriolis force) and centrifugal force, as well as under the influence of the friction force of air on the earth's surface. The Coriolis force affects every body moving along the meridian. Let 1 kg of air in the Northern Hemisphere be located at latitude µ and starts moving at speed V along the meridian to the north. This kilogram of air, like any body on Earth, has a linear rotation speed U=ωr, Where ω is the angular velocity of the Earth’s rotation, and r– distance to the axis of rotation. According to the law of inertia, this kilogram of air will maintain linear speed U, which he had at latitude µ . Moving north, he will be more high latitudes, where the radius of rotation is smaller and the linear speed of rotation of the Earth is smaller. Thus, this body will get ahead of stationary bodies located on the same meridian, but at higher latitudes.

For an observer, this will look like a deflection of this body to the right under the influence of some force. This force is the Coriolis force. By the same logic, a kilogram of air in the Southern Hemisphere will deviate to the left of the direction of movement. The horizontal component of the Coriolis force acting on 1 kg of air is equal to SC=2wVsinY. It deflects the air, acting at right angles to the velocity vector V. In the Northern Hemisphere, it deflects this vector to the right, and in the Southern Hemisphere, to the left. It follows from the formula that the Coriolis force does not arise if the body is at rest, i.e. it only works when the air is moving. In the Earth's atmosphere, the magnitudes of the horizontal pressure gradient and the Coriolis force are of the same order, so sometimes they almost balance each other. In such cases, the movement of air is almost rectilinear, and it does not move along the pressure gradient, but along the isobar or close to it.

Air currents in the atmosphere usually have a vortex nature, therefore, in such movement, centrifugal force acts on each unit of air mass P=V/R, Where V- wind speed, and R– radius of curvature of the motion trajectory. In the atmosphere, this force is always less than the force of the pressure gradient and therefore remains, so to speak, a force of “local significance”.

As for the friction force that arises between moving air and the surface of the Earth, it slows down the wind speed to a certain extent. It happens like this: the lower volumes of air, which have reduced their horizontal speed due to the unevenness of the earth's surface, are transferred upward from the lower levels. Thus, friction against the earth's surface is transmitted upward, gradually weakening. The slowdown in wind speed is noticeable in the so-called planetary boundary layer, amounting to 1.0 - 1.5 km. above 1.5 km the influence of friction is insignificant, therefore higher layers of air are called free atmosphere.

IN equatorial zone The linear speed of rotation of the Earth is the greatest, and accordingly, the Coriolis force is the greatest here. Therefore, in the tropical zone of the Northern Hemisphere, trade winds almost always blow from the northeast, and in the Southern Hemisphere - from the southeast.

Low pressure in the equatorial zone is observed constantly, in winter and summer. A band of low pressure that spans the entire globe along the equator is called equatorial trough.

Having gained strength over the oceans of both hemispheres, two trade wind flows, moving towards each other, rush to the center of the equatorial trough. On the low pressure line they collide, forming the so-called intertropical convergence zone(convergence means "convergence"). As a result of this “convergence”, an upward movement of air occurs and its outflow above the trade winds to the subtropics. This process creates the conditions for the existence of a convergence zone constantly, throughout the year. Otherwise, the converging air currents of the trade winds would quickly fill the hollow.

Rising movements of moist tropical air lead to the formation of a thick layer of cumulonimbus clouds with a length of 100–200 km, from which tropical showers fall. Thus it turns out that inside tropical zone convergence becomes a place where rains pour out from the steam collected by the trade winds over the oceans.

This is a simplified, schematic picture of the atmospheric circulation in the equatorial zone of the Earth.

Winds that change direction with the seasons are called monsoons. The Arabic word "mawsin", meaning "season", gives its name to these steady air currents.

Monsoons, unlike jet streams, occur in certain areas of the Earth where twice a year prevailing winds move in opposite directions, forming the summer and winter monsoons. The summer monsoon is a flow of air from the ocean to the mainland, the winter monsoon is from the mainland to the ocean. There are tropical and extratropical monsoons. In Northeast India and Africa, the winter tropical monsoons combine with the trade winds, while the summer southwestern monsoons completely destroy the trade winds. The most powerful tropical monsoons are observed in the northern Indian Ocean and South Asia. Extratropical monsoons originate in powerful, stable areas of high pressure that arise over the continent in winter and low pressure in summer.

Typical in this regard are the regions of the Russian Far East, China, and Japan. For example, Vladivostok, located at the latitude of Sochi, due to the action of the extratropical monsoon, is colder in winter than Arkhangelsk, and in summer there is often fog, precipitation, and moist and cool air comes from the sea.

Many tropical countries in South Asia receive moisture from the heavy rains of the summer tropical monsoon.

All winds are the result of the interaction of various physical factors occurring in the atmosphere over certain geographical areas. Local winds include breezes. They appear near the coastlines of seas and oceans and have a daily change of direction: during the day they blow from sea to land, and at night from land to sea. This phenomenon is explained by the difference in temperatures over the sea and land in different time days. The heat capacity of land and sea is different. During the day in warm weather Sun rays warm the land faster than the sea, and the pressure over the land decreases. The air begins to move towards lower pressure - it blows sea ​​breeze. In the evening, the opposite happens. The land and the air above it radiate heat faster than the sea, the pressure becomes higher than above the sea, and air masses rush towards the sea - it blows onshore breeze. Breezes are especially distinct in calm sunny weather, when nothing interferes with them, i.e. there are no other air currents that easily drown out breezes. The breeze speed is rarely higher than 5 m/s, but in the tropics, where the temperature difference between the sea and land surfaces is significant, breezes sometimes blow at a speed of 10 m/s. In temperate latitudes, breezes penetrate 25–30 km deep into the territory.

Breezes, in fact, are the same as monsoons, only on a smaller scale - they have a daily cycle and the change in direction depends on the change of night and day, while monsoons have an annual cycle and change direction depending on the time of year.

Ocean currents, meeting the shores of continents on their way, are divided into two branches directed along the coasts of the continents to the north and south. In the Atlantic Ocean, the southern branch forms the Brazil Current, washing the shores South America, and the northern branch is the warm Gulf Stream, turning into the North Atlantic Current, and under the name of the North Cape Current reaching the Kola Peninsula.

In the Pacific Ocean, the northern branch of the equatorial current passes into Kuro-Sivo.

We have previously mentioned the seasonal warm current off the coast of Ecuador, Peru and Northern Chile. It usually occurs in December (not every year) and causes a sharp decrease in fish catch off the coasts of these countries due to the fact that there is very little plankton in warm water - the main food resource for fish. A sharp increase in the temperature of coastal waters causes the development of cumulonimbus clouds, from which heavy rain falls.

The fishermen ironically called this warm current El Niño, which means “Christmas gift” (from the Spanish el ninjo - baby, boy). But we want to emphasize not the emotional perception of this phenomenon by Chilean and Peruvian fishermen, but its physical reason. The fact is that the increase in water temperature off the coast of South America is caused not only by warm current. Changes in the general situation in the ocean-atmosphere system in the vast expanses of the Pacific Ocean are also brought about by an atmospheric process called “ Southern Oscillation " This process, interacting with currents, determines all physical phenomena occurring in the tropics. All this confirms that the circulation of air masses in the atmosphere, especially over the surface of the World Ocean, is a complex, multidimensional process. But despite all the complexity, mobility and variability of air currents, there are still certain patterns due to which the main large-scale, as well as local processes of atmospheric circulation are repeated from year to year in certain areas of the Earth.

We conclude the chapter with some examples of the use of wind energy. People have been using wind energy since time immemorial, since they learned to sail at sea. Then windmills appeared, and later - wind engines - sources of electricity. Wind is an eternal source of energy, the reserves of which are incalculable. Unfortunately, using wind as a source of electricity is very difficult due to the variability of its speed and direction. However, with the help of wind electric motors, quite efficient use of wind energy has become possible. The blades of a windmill force it to almost always “keep its nose” in the wind. When the wind is strong enough, the current goes directly to consumers: for lighting, refrigeration units, appliances for various purposes, and for charging batteries. When the wind subsides, the batteries release the accumulated electricity to the grid.

At scientific stations in the Arctic and Antarctic, electricity from wind engines provides light and heat, and powers radio stations and other electricity consumers. Of course, at every research station there are diesel generators, for which you need to have a constant supply of fuel.

The very first navigators used the power of the wind spontaneously, without taking into account the system of winds and ocean currents. They simply knew nothing about the existence of such a system. Knowledge about winds and currents has accumulated over centuries and even millennia.

One of his contemporaries was the Chinese navigator Zheng He during 1405-1433. led several expeditions that passed the so-called Great Monsoon Route from the mouth of the Yangtze River to India and the eastern shores of Africa. Information has been preserved about the scale of the first of these expeditions. It consisted of 62 ships with 27,800 participants. For sailing expeditions, the Chinese used their knowledge of the patterns of monsoon winds. They left China for the sea at the end of November - beginning of December, when the northeast winter monsoon blows. A fair wind helped them reach India and East Africa. They returned to China in May - June, when the summer southwest monsoon set in, which became southern in the South China Sea.

Let's take an example from a time closer to us. We will talk about the travels of the famous Norwegian scientist Thor Heyerdahl. With the help of the wind, or rather, with the help of the trade winds, Heyerdahl was able to prove the scientific value of his two hypotheses. The first hypothesis was that the islands of Polynesia in the Pacific Ocean could, according to Heyerdahl, be inhabited sometime in the past by people from South America who crossed a large part of the Pacific Ocean on their primitive watercraft. These watercraft were rafts made of balsa wood, which is notable for the fact that after a long stay in the water it does not change its density and therefore does not sink.

The people of Peru have used such rafts for thousands of years, even before the Inca Empire. Thor Heyerdahl in 1947 knitted a raft from large balsa logs and named it “Kon-Tiki”, which means Sun-Tiki - the deity of the ancestors of the Polynesians. Taking five adventure lovers “on board” his raft, he set off under sail from Callao (Peru) to Polynesia. At the beginning of the voyage the raft was carried Peruvian Current and the southeastern trade wind, and then the eastern trade wind of the Pacific Ocean began to work, which blew regularly to the west for almost three months without a break, and after 101 days Kon-Tiki safely arrived on one of the islands of the Tuamotu archipelago (now French Polynesia).

Heyerdahl's second hypothesis was that he considered it quite possible that the culture of the Olmecs, Aztecs, Mayans and other tribes of Central America was transferred from Ancient Egypt. This was possible, according to the scientist, because once in ancient times people swam through Atlantic Ocean on papyrus boats. The trade winds also helped Heyerdahl prove the validity of this hypothesis.

Together with a group of like-minded companions, he made two voyages on papyrus boats “Ra-1” and “Ra-2”. The first boat (“Ra-1”) fell apart before reaching the American coast several tens of kilometers. The crew was in serious danger, but everything turned out well. The boat for the second voyage (“Ra-2”) was knitted by “high-class specialists” - Indians from the Central Andes. Leaving the port of Safi (Morocco), the papyrus boat “Ra-2” crossed the Atlantic Ocean after 56 days and reached the island of Barbados (approximately 300–350 km from the coast of Venezuela), covering a 6,100 km journey. At first the boat was driven by the northeast trade wind, and starting from the middle of the ocean - by the east trade wind.

The scientific nature of Heyerdahl's second hypothesis has been proven. But something else was also proven: despite the successful outcome of the voyage, a boat knitted from bundles of papyrus, reeds, reeds or other aquatic plants is not suitable for sailing in the ocean. Such “shipbuilding material” should not be used, because he quickly gets wet and sinks into the water. Well, if there are still amateurs obsessed with the desire to sail across the ocean on some exotic craft, then let them keep in mind that a balsa wood raft is more reliable than a papyrus boat, and also that such a trip is always and in any case dangerous.

© Vladimir Kalanov,
"Knowledge is power"

General circulation of the atmosphere is the circular movements of air masses that extend throughout the planet. They are carriers various elements and energy throughout the atmosphere.

Intermittent and seasonal distribution of thermal energy causes air currents. This leads to different warming of the soil and air in different areas.

That is why solar influence is the founder of the movement of air masses and atmospheric circulation. Air movements on our planet are completely different - reaching several meters or tens of kilometers.

The simplest and most understandable scheme for the circulation of the atmosphere of the ball was created many years ago and is used today. The movement of air masses is constant and non-stop; they move across our planet, creating a vicious circle. The speed of movement of these masses is directly related to solar radiation, interaction with the ocean and interaction of the atmosphere with the soil.

Atmospheric movements are caused by the instability of the distribution of solar heat throughout the planet. The alternation of opposite air masses - warm and cold - their constant abrupt movement up and down, forms various circulation systems.

The atmosphere receives heat in three ways - using solar radiation, through steam condensation and heat exchange with the earth's cover.

Humid air is also important for saturating the atmosphere with heat. The tropical Pacific Ocean plays a huge role in this process.

Air currents in the atmosphere

(Air flows in the Earth's atmosphere)

Air masses differ in their composition, depending on the place of origin. Air flows are divided into 2 main criteria - continental and sea. Continental ones are formed above the soil cover, so they are little moistened. Sea waters, on the contrary, are very wet.

The main air currents of the Earth are trade winds, cyclones and anticyclones.

Trade winds form in the tropics. Their movement is directed towards equatorial territories. This is due to pressure differences - at the equator it is low, and in the tropics it is high.

(Trade winds are shown in red on the diagram.)

Cyclone formation occurs above the surface warm waters. Air masses move from the center to the edges. Their influence is characterized by heavy rainfall and strong winds.

Tropical cyclones act over the oceans in equatorial areas. They form at any time of the year, causing hurricanes and storms.

Anticyclones form over continents where humidity is low, but there is a sufficient amount of solar energy. Air masses in these flows move from the edges to the central part, in which they heat up and gradually decrease. This is why cyclones bring clear and calm weather.

Monsoons are variable winds whose direction changes seasonally.

Secondary air masses such as typhoons, tornadoes, and tsunamis are also identified.

In the atmosphere, these are pressure differences in the layers of the atmosphere, of which there are several above the ground. Below you feel the greatest density and oxygen saturation. When a gaseous substance rises as a result of heating, a rarefaction occurs below, which tends to fill with adjacent layers. Thus, winds and hurricanes arise due to daytime and evening temperature changes.

Why is wind needed?

If there were no reason for the movement of air in the atmosphere, then the vital activity of any organism would cease. The wind helps plants and animals reproduce. He moves the clouds and is driving force in the water cycle on Earth. Thanks to climate change, the area is cleared of dirt and microorganisms.

A person can survive without food for about several weeks, without water for no more than 3 days, and without air for no more than 10 minutes. All life on Earth depends on oxygen, which moves along with the air masses. The continuity of this process is maintained by the sun. The change of day and night leads to temperature fluctuations on the surface of the planet.

There is always movement of air in the atmosphere, pressing on the surface of the Earth with a pressure of 1.033 g per millimeter. A person practically does not feel this mass, but when it moves horizontally, we perceive it as wind. In hot countries, the breeze is the only relief from the growing heat in the desert and steppes.

How is wind formed?

The main reason for air movement in the atmosphere is the displacement of layers under the influence of temperature. Physical process associated with the properties of gases: change their volume, expand when heated and contract when exposed to cold.

The main and additional reason for the movement of air in the atmosphere:

• Temperature changes under the influence of the sun are uneven. This is due to the shape of the planet (in the form of a sphere). Some parts of the Earth warm up less, others more. An atmospheric pressure difference is created.
• Volcanic eruptions sharply increase air temperatures.
• Heating of the atmosphere as a result of human activity: vapor emissions from cars and industry increase the temperature on the planet.
• Cooling oceans and seas at night cause air movement.
• Explosion atomic bomb leads to rarefaction in the atmosphere.

The mechanism of movement of gaseous layers on the planet

The reason for the movement of air in the atmosphere is uneven temperatures. The layers heated from the Earth's surface rise upward, where the density of the gaseous substance increases. A chaotic process of mass redistribution begins - the wind. Heat is gradually transferred to neighboring molecules, which also leads them into vibrational-translational motion.

The reason for the movement of air in the atmosphere is the relationship between temperature and pressure in gaseous substances. The wind continues until the initial state of the planet's layers is balanced. But such a condition will never be achieved due to the following factors:

• Rotational and translational motion of the Earth around the Sun.
• The inevitable unevenness of warmed areas of the planet.
• The activities of living beings directly affect the state of the entire ecosystem.

In order for the wind to completely disappear, it is necessary to stop the planet, remove all life from the surface and hide it in the shadow of the Sun. Such a state can occur with the complete destruction of the Earth, but scientists’ forecasts are so far comforting: this awaits humanity in millions of years.

Strong sea wind

Stronger air movement in the atmosphere is observed on the coasts. This is due to uneven heating of the soil and water. Rivers, seas, lakes, and oceans heat up less. The soil heats up instantly, giving off heat to the gaseous substance above the surface.

The heated air rushes upward sharply, and the resulting vacuum tends to fill. And since the air density above the water is higher, it forms towards the coast. This effect is especially noticeable in hot countries. daytime. At night the whole process changes, air movement towards the sea is already observed - the night breeze.

In general, a breeze is a wind that changes direction twice in a day to opposite directions. Monsoons have similar properties, only they blow in the hot season from the sea, and in cold seasons - towards the land.

How is wind determined?

The main reason for air movement in the atmosphere is uneven distribution of heat. The rule is true in any situation in nature. Even a volcanic eruption first heats the gaseous layers, and only then the wind rises.

You can check all processes by installing weather vanes, or, more simply, flags sensitive to air flow. The flat shape of the freely rotating device prevents it from being across the wind. It tries to turn in the direction of movement of the gaseous substance.

Often the wind is felt by the body, in the clouds, in the smoke of a chimney. Its weak currents are difficult to notice; to do this, you need to wet your finger, it will freeze on the windward side. You can also use a light piece of cloth or a balloon filled with helium, so the flag is raised on the masts.

Wind power

Not only the reason for the movement of air is important, but also its strength, determined on a ten-point scale:

• 0 points - wind speed in absolute calm;
• up to 3 - weak or moderate flow up to 5 m/sec;
• from 4 to 6 - strong wind speed about 12 m/sec;
• from 7 to 9 points - speed up to 22 m/sec is announced;
• from 8 to 12 points and above - called a hurricane, it even blows off the roofs of houses and collapses buildings.

or a tornado?

The movement causes mixed air currents. The oncoming flow is not able to overcome the dense barrier and rushes upward, piercing the clouds. After passing through the clots of gaseous substances, the wind falls down.

Conditions often arise when flows swirl and are gradually strengthened by suitable winds. The tornado gains strength and the wind speed becomes such that a train can easily soar into the atmosphere. North America leads in the number of such events per year. Tornadoes cause millions of losses for the population, they take away a large number of lives.

Other options for wind formation

Strong winds can erase any formations, even mountains, from the surface. The only type of non-temperature cause of air mass movement is a blast wave. After the atomic charge is triggered, the speed of movement of the gaseous substance is such that it demolishes multi-ton structures like specks of dust.

A strong flow of atmospheric air occurs when large meteorites fall or faults in the earth's crust. Similar phenomena are observed during a tsunami after earthquakes. Melting polar ice leads to similar conditions in the atmosphere.

Condensation is a change in the state of a substance from gaseous to liquid or solid. But what is condensation in the mastaba of the planet?

At any given time, the atmosphere of planet Earth contains over 13 billion tons of moisture. This figure is practically constant, since losses due to precipitation are ultimately continuously replenished by evaporation.

The rate of moisture circulation in the atmosphere

The rate of moisture circulation in the atmosphere is estimated at a colossal figure - about 16 million tons per second or 505 billion tons per year. If all the water vapor in the atmosphere suddenly condensed and fell as precipitation, this water could cover the entire surface of the globe with a layer of about 2.5 centimeters, in other words, the atmosphere contains an amount of moisture equivalent to only 2.5 centimeters of rain.

How long does a vapor molecule stay in the atmosphere?

Since the average annual precipitation on Earth is 92 centimeters, it follows that moisture in the atmosphere is renewed 36 times, that is, 36 times the atmosphere is saturated with moisture and freed from it. This means that a molecule of water vapor stays in the atmosphere for an average of 10 days.

Path of the water molecule

Once evaporated, a molecule of water vapor usually drifts for hundreds and thousands of kilometers until it condenses and falls with precipitation on the Earth. Water, snow or hail at higher elevations Western Europe, travels approximately 3000 km from the North Atlantic. Several physical processes occur between liquid water turning into vapor and precipitation falling on Earth.

From the warm surface of the Atlantic, water molecules enter the warm wet air, which subsequently rises above the surrounding colder (more dense) and drier air.

If strong turbulent mixing of air masses is observed, then a layer of mixing and clouds will appear in the atmosphere at the boundary of two air masses. About 5% of their volume is moisture. Air saturated with steam is always lighter, firstly, because it is heated and comes from a warm surface, and secondly, because 1 cubic meter of pure steam is about 2/5 lighter than 1 cubic meter of clean dry air at the same temperature and pressure. It follows that moist air is lighter than dry air, and warm and humid air even more so. As we will see later, this is very important fact for weather change processes.

Movement of air masses

Air can rise for two reasons: either because it becomes lighter as a result of heating and humidification, or because forces act on it, causing it to rise above some obstacles, such as over masses of colder and denser air or over hills and mountains.

Cooling

Rising air entering layers with less atmospheric pressure, is forced to expand and cool at the same time. Expansion requires the expenditure of kinetic energy, which is taken from the thermal and potential energy of atmospheric air, and this process inevitably leads to a decrease in temperature. The cooling rate of a rising portion of air often changes if this portion is mixed with surrounding air.

Dry adiabatic gradient

Dry air, in which there is no condensation or evaporation, and no mixing, and does not receive energy in any other form, cools or warms by a constant amount (1 ° C every 100 meters) as it rises or falls. This quantity is called the dry adiabatic gradient. But if the rising air mass is moist and condensation occurs in it, then latent heat of condensation is released and the temperature of the steam-saturated air drops much more slowly.

Moist adiabatic gradient

This amount of temperature change is called the moist-adiabatic gradient. It is not constant, but changes with changes in the amount of latent heat released, in other words, it depends on the amount of condensed steam. The amount of steam depends on how much the air temperature drops. In the lower layers of the atmosphere, where the air is warm and humidity is high, the moist-adiabatic gradient is slightly more than half the dry-adiabatic gradient. But the moist-adiabatic gradient gradually increases with height and by a very high altitude in the troposphere is almost equal to the dry adiabatic gradient.

The buoyancy of moving air is determined by the relationship between its temperature and the temperature of the surrounding air. Typically, in the real atmosphere, air temperature falls unevenly with height (this change is simply called a gradient).

If the air mass is warmer and therefore less dense than the surrounding air (and the moisture content is constant), then it rises upward in the same way as a child's ball immersed in a tank. Conversely, when the moving air is colder than the surrounding air, its density is higher and it sinks. If the air has the same temperature as neighboring masses, then their density is equal and the mass remains motionless or moves only with the surrounding air.

Thus, there are two processes in the atmosphere, one of which promotes the development of vertical air movement, and the other slows it down.

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Air masses- these are the moving parts of the troposphere, differing from each other in their properties - temperature, transparency. These properties of air masses depend on the territory over which they are formed under the condition of a long stay. Depending on the formation, there are 4 main types of air masses: (), tropical and. Each of these four types is formed over an area of ​​land and sea. Since land and sea heat up to different degrees, subtypes can form in each of these types - continental and marine air masses.

Arctic (Antarctic) air forms over the icy surface of polar latitudes; characterized low temperatures, low moisture content, while the Arctic sea air is more humid than continental air. Invading low latitudes, Arctic air significantly lowers temperatures. The flat terrain facilitates its penetration far into the interior of the continent. A similar phenomenon can be observed. As it moves south, the Arctic air warms up and contributes to the formation of dry winds, which cause frequent winds in the area.

Moderate air masses form in temperate latitudes. Continental temperate air masses are greatly cooled in winter. They have a low moisture content. With the invasion of continental air masses, clear frosty weather sets in. In summer, continental air is dry and very hot. Marine air masses of temperate latitudes are humid, moderate; In winter they bring thaws, in summer they bring cloudy weather and colder temperatures.

Tropical air masses all year round are formed in the tropics. Typically, their marine variety is characterized by high humidity and temperature, while the continental variety is dusty, dry, and even more so. high temperature.

Equatorial air masses are formed in the equatorial zone. around its axis contributes to the movement of air masses either to the Northern Hemisphere or to the Southern Hemisphere. These air masses are characterized by high temperature and high humidity, and there is no clear division for them into marine air masses and continental ones.

The resulting air masses inevitably begin to move. The reason for this is the uneven heating of the earth's surface and, as a consequence, the difference. If there were no movement of air masses, then at the equator the average annual temperature would be 13° higher, and at latitudes 70° - 23° lower than at present.

Invading areas with different surface thermal properties, air masses are gradually transformed. For example, temperate sea air, entering land and moving inland, gradually heats up and dries out, turning into continental air. The transformation of air masses is especially characteristic of temperate latitudes, into which warm and dry air from the latitudes and cold and dry air from the subpolar ones invade from time to time.