Interaction between the ocean and the atmosphere.

27. Circulation of air masses.

© Vladimir Kalanov,
"Knowledge is power".

moving air masses in the atmosphere is determined by the thermal regime and changes in air pressure. The totality of the 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 currents in cyclones and anticyclones, trade winds and monsoons.

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

It is not entirely clear how the wind speed changes over the continents at low altitudes (100–200 m). here the wind speeds reach their highest values ​​in the afternoon, and the lowest ones at night. It is best seen in summer.

Very strong winds, up to stormy ones, 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, a completely opposite picture is observed: a maximum speed at night and a minimum during the day. The same picture is observed both in summer and winter in temperate latitudes.

Gusty winds can bring a lot of trouble to pilots of airplanes and helicopters. Jets of air moving in different directions, in jolts, gusts, either weakening or intensifying, create a large obstacle to the movement of aircraft - a chatter appears - a dangerous violation of normal flight.

Winds blowing from the mountain ranges of the cold mainland in the direction warm sea, are called bora. It is a strong, cold, gusty wind that usually blows during the cold season.

Bora is known to many in the region of Novorossiysk, on the Black Sea. Here such natural conditions that the speed of the bora can reach 40 and even 60 m/s, while the air temperature drops to minus 20°C. Bora occurs most often between September and March, on average 45 days a year. Sometimes its consequences were as follows: the harbor froze, ships, buildings, the embankment were covered with ice, roofs were torn off houses, wagons overturned, ships were thrown ashore. Bora is also observed in other regions of Russia - on 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 appear in the atmosphere with fast spiraling air movement. These whirlwinds are called tornadoes (in America they are called tornadoes). Tornadoes are several tens of meters in diameter, sometimes up to 100–150 m. It is extremely difficult to measure the air velocity inside a tornado. According to the nature of the damage produced by the tornado, the estimated velocities may well be 50–100 m/s, and in especially strong eddies, up to 200–250 m/s with a large vertical velocity component. The pressure in the center of the ascending tornado column drops by several tens of millibars. Millibars for determining pressure are usually used in synoptic practice (along with millimeters of mercury). To convert bars (millibars) to mm. mercury column, there are special tables. In the SI system, atmospheric pressure is measured in hectopascals. 1hPa=10 2 Pa=1mb=10 -3 bar.

Tornadoes exist for a short time - from several minutes to several hours. But for this little time they manage to do a lot of trouble. When a tornado approaches (over land, tornadoes are sometimes called blood clots) to 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, windows and frames fly out, roofs are torn off, sometimes it cannot do without human victims. There are times when a tornado lifts people, animals, and various objects into the air and transports them to tens or even hundreds of meters. In their movement, tornadoes move several tens of kilometers above 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, more often they occur 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 geographical latitude and height above sea level. The density of air is the mass per unit of its volume. The density of moist and dry air differs markedly only at high temperature and high humidity. As the temperature decreases, the density increases; with height, the air density decreases more slowly than the pressure. Air density is usually not directly measured, but calculated from equations based on the measured values ​​of temperature and pressure. Indirectly, air density is measured by the deceleration of artificial Earth satellites, as well as from observations of the spreading of artificial clouds of sodium vapor created by meteorological 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 dependence. The equation expressing the law of change in pressure with height in an atmosphere at rest is called the basic equation of statics. It follows from it that with increasing altitude, the change in pressure is negative, and when ascending to the same height, the pressure drop is the greater, 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 the air. In addition to the force of the pressure gradient in the atmosphere, there are inertial forces (Coriolis force and centrifugal force), as well as the friction force. All air currents are considered relative to the Earth, which rotates around its axis.

The spatial distribution of atmospheric pressure is called the baric 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).
The surfaces are drawn through equal intervals of pressure p.

Isobaric surfaces cannot be parallel to each other and the earth's surface, because temperature and pressure are constantly changing in the horizontal direction. Therefore, isobaric surfaces have a diverse appearance - from shallow "hollows" bent downwards to stretched "hills" curved 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 built based on the results of observations at a certain point in time, are called synoptic maps. Isobar maps, compiled from long-term average 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 taken between isobars.

On maps of a limited area, the isobars may break off, but on a map of the entire globe, each isobar is, of course, 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 is meant a huge whirlwind in the lower layer of the atmosphere, having a reduced atmospheric pressure in the center and an upward movement of air masses. In a cyclone, pressure increases from the center to the periphery, and 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 look like swirling cloud spirals in temperate latitudes.

Anticyclone is an area of ​​high pressure. It occurs 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 appearance of powerful clouds and prolonged precipitation.

Thus, large-scale atmospheric circulation in temperate latitudes is constantly reduced 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 the polar latitudes. On the contrary, anticyclones that arise in the rear of cyclones in a cold air mass move to subtropical latitudes, transferring cold air there.

Over the European territory of Russia, an average of 75 cyclones occur annually. 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 pressure in the center of more than 1050 hPa. The average pressure in the Northern Hemisphere at sea level 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 of low pressure, called Icelandic And Aleutian depressions. depression, or pressure minima, are characterized by minimum pressure values ​​- on average, about 995 hPa.

In the same period of the year, high pressure areas appear 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 pressure is recorded 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 up and give way to anticyclones. The Asian and Canadian anticyclones arise due to the presence at these latitudes of the vast continents of Eurasia and North America. In these areas, anticyclones prevail over cyclones in winter.

In summer, over these continents, the scheme of the baric 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 above the uniform surface of the oceans, moving southeast, meet the ice of Antarctica and stagnate here, having low air pressure at their centers. In winter and summer, Antarctica is surrounded by a low pressure belt (985–990 hPa).

In subtropical latitudes, the circulation of the atmosphere is different over the oceans and in the areas where the continents and oceans meet. Above the Atlantic and Pacific oceans in the subtropics of both hemispheres there are areas of high pressure: these are the Azores and South Atlantic subtropical anticyclones (or baric 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 ° north and south latitude along the equator) during all year round low atmospheric pressure is maintained, and in tropical latitudes, in the band 30–40 ° N. and y.sh. - increased, as a result of which constant air flows are formed, 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 insignificant limits. These are the most stable winds on Earth. The force of the horizontal baric gradient directs air flows from areas of high pressure to areas of low pressure in the meridional direction, i.e. south and north. Note: The horizontal baric gradient is the pressure difference per unit distance along the normal to the isobar.

But the meridional direction of the trade winds changes under the action of two forces of inertia - the deflecting force of the Earth's rotation (Coriolis force) and centrifugal force, as well as under the action of the air friction force on the earth's surface. The Coriolis force acts on every body moving along the meridian. Let 1 kg of air in the Northern Hemisphere be located at latitude µ and starts moving at a speed V along the meridian to the north. This kilogram of air, like any body on Earth, has a linear speed of rotation U=ωr, Where ω is the angular velocity of the Earth's rotation, and r is the distance to the axis of rotation. According to the law of inertia, this kilogram of air will maintain linear velocity U, which he had at latitude µ . Moving north, it will find itself at higher latitudes, where the radius of rotation is smaller and the linear velocity of the Earth's rotation is lower. Thus, this body will outstrip the motionless 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 action 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 motion. The horizontal component of the Coriolis force acting on 1 kg of air is 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 values ​​of the horizontal baric 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 or close to the isobar.

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

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

In the equatorial zone, the linear velocity of the Earth's rotation is the highest, respectively, here the Coriolis force is the highest. Therefore, in the tropical zone of the Northern Hemisphere, the 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. The band of low pressure that surrounds the entire globe at the equator is called equatorial trough.

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

Ascending movements of humid tropical air lead to the formation of a powerful layer of cumulonimbus clouds 100–200 km long, from which tropical showers fall. Thus it turns out that the intratropical convergence zone becomes the place where the rains pour out from the steam collected by the trade winds over the oceans.

So simplified, schematically looks like a picture of the circulation of the atmosphere in the equatorial zone of the Earth.

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

Monsoons, unlike jet streams, occur in certain areas of the Earth where twice a year the prevailing winds move in opposite directions, forming the summer and winter monsoons. The summer monsoon is the flow of air from the ocean to the mainland, while the winter monsoon is from the mainland to the ocean. Tropical and extratropical monsoons are known. In Northeast India and Africa, the winter tropical monsoons combine with the trade winds, while the summer southwest monsoons completely destroy the trade winds. The most powerful tropical monsoons are observed in the northern part of the Indian Ocean and in South Asia. Extratropical monsoons originate in powerful stable areas of high pressure arising 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, which lies at the latitude of Sochi due to the action of the extratropical monsoon, is colder than Arkhangelsk in winter, and in summer there are often fogs, precipitation, moist and cool air comes from the sea.

Many tropical countries in South Asia receive moisture brought in the form of heavy rains by the summer tropical monsoon.

Any winds are the result of the interaction of various physical factors that occur in the atmosphere over certain geographical areas. The local winds are breezes. They appear near the coastline of the seas and oceans and have a daily change of direction: during the day they blow from the sea to land, and at night from land to sea. This phenomenon is explained by the difference in temperatures over the sea and land at different times of the day. The heat capacity of land and sea is different. During the day in warm weather, the sun's rays heat the land faster than the sea, and the pressure over the land decreases. Air begins to move in the direction of lower pressure - blowing sea ​​breeze. In the evening, everything happens the other way around. The land and the air above it radiate heat faster than the sea, the pressure becomes higher than over the sea, and the air masses rush towards the sea - blowing coastal breeze. The breezes are especially distinct in calm sunny weather, when nothing interferes with them, i.e. other air currents are not superimposed, which easily drown out the breezes. The speed of the breeze 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 monsoons, only on a smaller scale - they have a daily cycle and change 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 coasts of the 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, which passes into the North Atlantic Current, and under the name of the North Cape Current reaches 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 coast of these countries due to the fact that there is very little plankton in warm water - the main food resource for fish. Rapid rise in temperature coastal waters causes the development of cumulonimbus clouds, from which heavy rains are shed.

The fishermen ironically called this warm current El Nino, which means "Christmas present" (from the Spanish el ninjo - baby, boy). But we want to emphasize not the emotional perception of the Chilean and Peruvian fishermen of this phenomenon, but its physical cause. The fact is that the increase in water temperature off the coast of South America is caused not only by a warm current. Changes in the general situation in the "ocean-atmosphere" system in the vast expanses of the Pacific Ocean are also introduced by the atmospheric process, called " Southern Oscillation". This process, interacting with currents, determines everything 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 with all the complexity, mobility and variability of air currents, there are still certain patterns, due to which in certain regions of the Earth, the main large-scale, as well as local processes of atmospheric circulation are repeated from year to year.

In conclusion of the chapter, we give some examples of the use of wind energy. People have been using wind energy since time immemorial, ever since they learned how to sail the sea. Then there were windmills, and later - wind engines - sources of electricity. Wind is an eternal source of energy, the reserves of which are incalculable. Unfortunately, the use of wind as a source of electricity is very difficult due to the variability of its speed and direction. However, with the help of wind turbines, it has become possible to use wind energy quite efficiently. The blades of a windmill make it almost always "keep its nose" in the wind. When the wind has sufficient strength, the current goes directly to consumers: for lighting, for refrigeration units, for various devices and for charging batteries. When the wind subsides, the batteries transfer the accumulated electricity to the grid.

At scientific stations in the Arctic and Antarctic, the electricity from wind turbines provides light and heat, ensures the operation of radio stations and other consumers of electricity. Of course, at each scientific 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 did not know anything about the existence of such a system. Knowledge about winds and currents has been accumulated over centuries and even millennia.

One of the 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 about the scale of the first of these expeditions has been preserved. It consisted of 62 ships with 27,800 participants. For sailing expeditions, the Chinese used their knowledge of the patterns of monsoon winds. From China, they went to sea in late November - early 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 was established, which became south in the South China Sea.

Let's take an example from a time closer to us. It will be 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 at some time in the past by immigrants from South America who crossed a significant part of the Pacific Ocean on their primitive watercraft. These boats 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.

Peruvians have been using these rafts for thousands of years, even before the Inca Empire. Thor Heyerdahl in 1947 tied a raft of large balsa logs and named it "Kon-Tiki", which means the Sun-Tiki - the deity of the ancestors of the Polynesians. Taking five adventurers on board his raft, he set sail from Callao (Peru) to Polynesia. At the beginning of the voyage, the raft carried the Peruvian current and the southeast trade wind, and then the east trade wind of the Pacific Ocean set to work, which for almost three months without interruption blew regularly to the west, 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, Maya and other tribes of Central America was transferred from Ancient Egypt. This was possible, according to the scientist, because once in ancient times people sailed across the Atlantic Ocean on papyrus boats. The trade winds also helped Heyerdahl to prove the validity of this hypothesis.

Together with a group of like-minded satellites, he made two voyages on papyrus boats "Ra-1" and "Ra-2". The first boat ("Ra-1") fell apart before reaching the American coast for 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 "specialists upper class" - Indians from the Central Andes. Leaving the port of Safi (Morocco), the papyrus boat "Ra-2" after 56 days crossed the Atlantic Ocean and reached the island of Barbados (about 300-350 km from the coast of Venezuela), having overcome 6100 km of the way. At first, the northeast trade wind drove the boat, and starting from the middle of the ocean, 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 tied from bundles of papyrus, reeds, reeds or other aquatic plants is not suitable for swimming in the ocean. Such "shipbuilding material" should not be used, as it quickly gets wet and sinks into the water. Well, if there are still amateurs who are obsessed with the desire to swim across the ocean on some exotic watercraft, then let them keep in mind that a balsa wood raft is more reliable than a papyrus boat, and also that such a journey is always and in any case dangerous.

© Vladimir Kalanov,
"Knowledge is power"

The atmosphere is not uniform. In its composition, especially near the earth's surface, air masses can be distinguished.

Air masses are separate large volumes of air that have certain common properties(temperature, humidity, transparency, etc.) and moving as a whole. However, within this volume, the winds can be different. The properties of the air mass are determined by the region of its formation. It acquires them in the process of contact with the underlying surface, over which it forms or lingers. Air masses have different properties. For example, the air of the Arctic has low temperatures, while the air of the tropics has high temperatures in all seasons of the year, the air of the North Atlantic differs significantly from the air of the Eurasian continent. The horizontal dimensions of air masses are enormous, they are commensurate with the continents and oceans or their large parts. There are main (zonal) types of air masses formed in belts with different atmospheric pressure: arctic (antarctic), temperate (polar), tropical and equatorial. Zonal air masses are divided into maritime and continental - depending on the nature of the underlying surface in the area of ​​their formation.

Arctic air is formed over the Arctic Ocean, and in winter also over the north of Eurasia and North America. The air is characterized by low temperature, low moisture content, good visibility and stability. Its intrusions into temperate latitudes cause significant and sharp cooling and determine predominantly clear and slightly cloudy weather. Arctic air is divided into the following varieties.

Maritime Arctic air (mAv) - formed in the warmer, ice-free European Arctic with higher temperature and higher moisture content. Its incursions into the mainland in winter cause warming.

Continental arctic air (cAv) - formed over the Central and Eastern icy Arctic and north coast continents (winter). The air is very low temperatures, low moisture content. The invasion of the KAV on the mainland causes a strong cooling in clear weather and good visibility.

An analogue of the Arctic air in the Southern Hemisphere is the Antarctic air, but its influence extends mainly to the adjacent sea surfaces, less often to the southern tip of South America.

Moderate (polar) air. This is the air of temperate latitudes. It also has two subtypes. Continental temperate air (CW), which is formed over the vast surfaces of the continents. In winter it is very chilled and stable, the weather is usually clear with hard frosts. In summer, it gets very warm, ascending currents arise in it, clouds form, it often rains, thunderstorms are observed. Marine temperate air (MOA) is formed in the middle latitudes over the oceans, and is transported to the continents by westerly winds and cyclones. It is characterized by high humidity and moderate temperatures. In winter, MUW brings cloudy weather, heavy rainfall and higher temperatures (thaws). In summer it also brings a lot of cloudiness, rains; the temperature drops as it enters.

Temperate air penetrates into the polar, as well as subtropical and tropical latitudes.

Tropical air is formed in tropical and subtropical latitudes, and in summer - in continental regions in the south of temperate latitudes. There are two subtypes of tropical air. Continental tropical air (cT) is formed over land, characterized by high temperatures, dryness and dustiness. Marine tropical air (mTw) is formed over tropical areas (tropical ocean zones), characterized by high temperature and humidity.

Tropical air penetrates into temperate and equatorial latitudes.

Equatorial air is formed in the equatorial zone from tropical air brought by the trade winds. It is characterized by high temperatures and high humidity throughout the year. In addition, these qualities are preserved both over land and over the sea, therefore, equatorial air is not divided into marine and continental subtypes.

Air masses are in constant motion. Moreover, if the air masses move to higher latitudes or to a colder surface, they are called warm, since they bring warming. Air masses moving to lower latitudes or to a warmer surface are called cold air masses. They bring coldness.

Moving to other geographical areas, air masses gradually change their properties, primarily temperature and humidity, i.e. move into other types of air masses. The process of transformation of air masses from one type to another under the influence of local conditions is called transformation. For example, tropical air, penetrating towards the equator and into temperate latitudes, is transformed into equatorial and temperate air, respectively. Marine temperate air, once in the depths of the continents, cools in winter, and heats up in summer and always dries up, turning into temperate continental air.

All air masses are interconnected in the process of their constant movement, in the process general circulation troposphere.

In the atmosphere, these are pressure drops in the layers of the atmosphere, of which there are several above the earth. At the bottom, the greatest density and saturation with oxygen is felt. When a gaseous substance rises as a result of heating, a rarefaction occurs below, which tends to be filled with neighboring layers. So winds and hurricanes arise due to daytime and evening temperature changes.

Why is wind needed?

If there was 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. It moves clouds and is the 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 moving along with air masses. The continuity of this process is supported by the sun. The change of day and night leads to fluctuations in temperature on the surface of the planet.

In the atmosphere, there is always a movement of air 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 the movement of air in the atmosphere is the displacement of layers under the influence of temperature. The physical process is associated with the properties of gases: change their volume, expand when heated and contract when 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. A difference in atmospheric pressure is created.
• Volcanic eruptions dramatically increase the air temperature.
• Heating of the atmosphere as a result of human activity: fumes from cars and industry increase the temperature on the planet.
• Cooled oceans and seas cause air to move at night.
• The explosion of an atomic bomb causes a 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 the uneven temperature. The layers heated from the surface of the Earth rise upwards, where the density of the gaseous substance increases. A chaotic process of redistribution of masses begins - the wind. Heat is gradually given off to neighboring molecules, which also leads them into oscillatory-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.
• Inevitable unevenness of the heated parts 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 from the Sun. Such a state can occur with the complete death of the Earth, but the forecasts of scientists are still comforting: this is expected by humanity in millions of years.

strong sea wind

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

The heated air rushes up sharply, and the resulting rarefaction tends to fill up. And since the air density above the water is higher, it is formed towards the coast. This effect is especially well felt in hot countries during the daytime. At night, the whole process changes, there is already a movement of air towards the sea - a night breeze.

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

How is wind determined?

The main reason for the movement of air in the atmosphere is the uneven distribution of heat. The rule is true in all situations 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 that are sensitive to air flow. The flat shape of a freely rotating device does not allow it to be across the wind. It tries to turn in the direction of movement of the gaseous substance.

Often the wind is felt by the body, through the clouds, through the smoke. chimney. It is difficult to notice its weak flows, for this you need to wet your finger, it will freeze from 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 / s;
• from 4 to 6 - strong wind speed of about 12 m / s;
• from 7 to 9 points - speed up to 22 m / s is announced;
• from 8 to 12 points and above - is called a hurricane, even demolishes roofs from houses, buildings collapse.

or tornado?

The movement causes mixed currents of air. The oncoming flow is not able to overcome the dense barrier and rushes up, penetrating the clouds. Having passed clots of gaseous substances, the wind falls down.

Often there are conditions when there is a twisting of flows, gradually intensifying by suitable winds. The tornado is gaining strength and the wind speed is such that a train can easily soar into the atmosphere. North America is the leader in the number of such events per year. Tornadoes cause millions of losses for the population, they carry away a large number of lives.

Other wind generation options

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

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

Condensation is the 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 the planet Earth contains over 13 billion tons of moisture. This figure is almost constant, as losses due to precipitation are eventually continuously replaced by evaporation.

Moisture cycle rate in the atmosphere

The rate of circulation of moisture in the atmosphere is estimated at a colossal figure - about 16 million tons per second or 505 billion tons per year. If suddenly all the water vapor in the atmosphere condensed and fell out as precipitation, then this water could cover the entire surface the globe 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 on Earth an average of 92 centimeters falls per year, therefore, 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 water vapor molecule stays in the atmosphere for an average of 10 days.

Water molecule path

Once evaporated, a water vapor molecule usually drifts hundreds and thousands of kilometers until it condenses and falls to the Earth with precipitation. Water falling as rain, snow, or hail at higher elevations Western Europe, overcomes approximately 3000 km from the North Atlantic. Between the transformation of liquid water into steam and the precipitation on Earth, several physical processes take place.

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 in this case a strong turbulent mixing of air masses is observed, then a layer of mixing and clouds will appear in the atmosphere at the border of two air masses. About 5% of their volume is moisture. Steam-saturated air 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 is 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 moisture, or because forces act on it, causing it to rise above some obstacles, such as masses of colder and denser air, or over hills and mountains.

Cooling

Rising air, having fallen into layers with lower atmospheric pressure, is forced to expand and at the same time cool. 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 the surrounding air.

Dry adiabatic gradient

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

Wet adiabatic gradient

This amount of temperature change is called the wet-adiabatic gradient. It is not constant, but changes with 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 wet-adiabatic gradient is slightly more than half of the dry-adiabatic gradient. But the wet-adiabatic gradient gradually increases with height and at a very high altitude in the troposphere is almost equal to the dry-adiabatic gradient.

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

If the mass of air is warmer and therefore less dense than the surrounding air (and the moisture content is constant), then it rises 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 the neighboring masses, then their density is equal and the mass remains stationary or moves only together 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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Ever since I was a child, I have been fascinated by the invisible movements around us: a gentle breeze swirling autumn leaves in a cramped courtyard, or a powerful winter cyclone. It turns out that these processes have quite understandable physical laws.

What forces cause air masses to move

Warm air is lighter than cold air - this simple principle can explain the movement of air on the planet. It all starts at the equator. Here, the sun's rays fall on the Earth's surface at a right angle, and a small particle of equatorial air gets a little more heat than neighboring ones. This warm particle becomes lighter than the neighboring ones, which means it starts to float up until it loses all the heat and starts to sink again. But downward movement is already taking place in the thirtieth latitudes of the Northern or Southern Hemisphere.

If there were no additional forces, the air would move from the equator to the poles. But there is not one, but several forces at once that make air masses move:

• The power of buoyancy. When warm air rises and cold air stays down.
• Coriolis force. I'll tell you about it a little lower.
• The relief of the planet. Combinations of seas and oceans, mountains and plains.

The deflecting force of the Earth's rotation

It would be easier for meteorologists if our planet did not rotate. But she's spinning! This generates the deflecting force of the Earth's rotation or the Coriolis force. Due to the motion of the planet, that very “light” particle of air is not only displaced, say, to the north, but also shifts to the right. Or it is forced out to the south and deviates to the left.

This is how they are born constant winds western or eastern directions. You may have heard of the flow West Winds or the Roaring Forties? These constant movements of air arose precisely because of the Coriolis force.

Seas and oceans, mountains and plains

The relief brings the final confusion. The distribution of land and ocean changes the classical circulation. So, in the Southern Hemisphere, there is much less land than in the Northern, and nothing prevents the air from moving over the water surface in the direction it needs, there are no mountains or large cities, while the Himalayas radically change the air circulation in their area.