Why in temperate latitudes most often. School stage of the All-Russian Olympiad for schoolchildren in geography (3) - Document

Westerly winds of temperate latitudes are winds that occur due to different pressures in the atmosphere. Mostly they are formed on the border between land and oceans, seas. From the name, you can determine the areas where they can blow - in southern and northern latitudes.

Where can they form

Westerly winds of temperate latitudes are movements of air masses that have a band of action ranging from 35 degrees north to 65 degrees south latitude. These borders are located between the subtropical ridge and end with the polar front. The winds form massive cyclones and whirlwinds that cover entire continents.

Mid-latitude westerly winds are sources of extratropical cyclones that dampen the tropical winds they encounter. But the latter are again intensified due to the eddy form of the westerly winds and become even more destructive. Wind strength also changes with the seasons.

AT winter period the speed of the cyclones increases significantly. The westerly winds of temperate latitudes are the prevailing moving air masses southern hemisphere. This is due to the huge space covered by the water column. Passing through land, the winds lose their strength.

The climate of the planet

The westerly winds of the temperate latitudes of the Southern Hemisphere affect the climate of the entire Earth. The force of movement of air masses determines how much heat or humidity will be displaced due to the difference in pressure over land and sea, ocean. The summer period is less windy due to the decrease in the pressure difference over the poles.

The westerly winds of the temperate latitudes of the Southern Hemisphere affect the climate not only of the surrounding air. The direction of ocean currents, the density of vegetation and the population of the animal world on land and in water depend on the strength of the winds. The direction of warm and

The westerly winds of temperate latitudes never subside. In the zone of their action, increased activity of cyclones, but in the equatorial part of the planet they still do not dominate. Subtropical cyclones rise here.

Seasons

The westerly winds of the temperate latitudes of the Southern Hemisphere blow throughout the year in the northern band from 60 degrees south latitude. Their average wind speed was recorded, ranging from 7 to 13 m/s. Often, these winds increase suddenly and cause devastating hurricanes. It is during the winter period in the subtropics that it is unsafe. There are a huge number of typhoons, tsunamis.

Western winds of temperate latitudes bring moisture to the coasts and at the same time take a significant part of the heat from the land. When the air moves from the coast to the ocean with great force, cyclic swirls begin to form for many kilometers. In pictures from space, you can see white clouds swirling in a spiral over the Pacific Ocean, seas, and the Atlantic. There are other names for the westerly winds according to latitude: the howling fifties and the roaring forties.

How cyclones form

Air gusts predominate in the stratosphere, and pressure drops also form in the troposphere. Moreover, areas with high pressure always belong there. The pressure of air masses is much higher and it practically does not subside.

Due to the formation of air irregularities, westerly winds of temperate latitudes begin to form. The causes of occurrence are associated with the heat received from the sun. The cyclones themselves, which are visible from space as swirling clouds, appear due to physical phenomena from the rotation of the planet.

A regularity has been established, westerly winds are trying to shift to the eastern hemisphere, which contributes to the formation of an air flow going from west to east. Uneven bands of cyclones shift depending on the time of year.

Names of air mass flows

Each movement of the air mass has its own name:

• Winds moving from north to east are called trade winds.
• The movement of masses in higher layers from south to west is called antitrade winds or westerly winds.

Western winds are also called "west release" or "belt of westerly winds", you can often hear a different name - "brave news". The higher the layers of air masses, the stronger the gusts occur, and the more constant they are. The area of ​​action of the winds expands proportionally with the rise.

The study of the winds was useful to navigators. Following the laws of wind movement, with the help of a sailboat it is possible to overcome huge distances Pacific Ocean. The name "trade wind" comes from the Dutch language and translated into Russian means "permanent". In the Middle Ages, sailors adapted to catch constant winds and there were entire sea routes. One of these sailing trips has gained popularity: from Europe straight to the New World.

Getting on land, they bring rain, squalls of water fall in a short period of time. Everyone knows sudden torrential tropical rains. They are manifestations of the trade winds.

The southern and northern trade winds are separated from each other by a strip of the intratropical zone. The counter interaction of cyclones is excluded due to the rotation of the planet. At the same time, the constancy of the trade winds is ensured. After all, they do not stop all year, only the strength of the wind changes.

natural patterns

Trade winds are able to intensify due to the vertical movement of air masses. Temperature fluctuations on the surface contribute to the rapid sinking heavy air from the upper layers of the atmosphere. Due to it, horizontal gusts are mixed with suitable gusts. The increase is sudden and leads to acceleration of the wind along the water surface. The gust is so strong that it comes to land in the form of a typhoon in a few hours.

Often, natural disasters on tropical islands take vacationers by surprise. Predicting the development of strong trade winds is extremely difficult. The increase in wind speed occurs according to the Coriolis laws, or, more simply, air flows are combined along the circumference. Where and at what moment the next change in pressure will occur, only scientists who observe events directly in the area of ​​the formation of the cataclysm can say.

Varieties of air currents

The trade winds over the oceans are characterized by heavy rainfall. Winds take moisture from the surface of the water. There are similar movements of air masses over deserts. They never bring "good news" to its inhabitants. There never it's raining not a drop of moisture falls on the hot earth.

These winds are also called trade winds, but not sea winds, but desert winds. They are dry due to the peculiar movement of air. Layers in these areas from the lower layers cannot rise higher, releasing all the moisture on the coast. Dry tropical air continues to move towards the land, blowing non-stop throughout the year.

main area extratropical latitudes occupy moderate zones. It is in them that atmospheric processes take place, which play a leading role in the circulation of the atmosphere, the formation of the weather and climate of these and adjacent latitudes. Temperate latitudes are characterized by western transport of air throughout the entire thickness of the atmosphere, due to thermal and dynamic factors. The exception is the eastern margins of the continents, where the monsoon transport of air masses is developed.

In the lower troposphere, westerly winds from the outer polar peripheries of subtropical oceanic baric maxima form the basis of the westerly transport. The latter are, as it were, the "wind divisions" of the Earth, from which the winds flow both to the equator (trade winds) and to temperate latitudes. Westerly winds are best expressed and most stable in the southern hemisphere. There, south of the subtropical belt of high pressure, pronounced in winter, but remaining in the form of an almost continuous band even in summer, there is a permanent belt of low pressure around Antarctica. In the northern hemisphere, there is a significant heterogeneity of the underlying surface (continents and oceans), significant seasonal contrasts of all meteorological characteristics and their rapid variability in

meridional direction lead to great instability of atmospheric processes. That's why the westerly winds are here in pure form inherent in the oceans and the western halves of the continents and are revealed only from a statistical analysis of long-term data.

Cyclones and anticyclones. A characteristic feature of temperate latitudes is the diversity of air masses: arctic (Antarctic), polar (they are dominant), tropical, both marine and continental, shifting from west to east and transforming at the same time. Between different air masses, atmospheric fronts constantly arise and also change their position, on which unstable waves are formed, giving rise to cyclones and anticyclones of temperate latitudes - large-scale atmospheric eddies with different wind systems that complicate the western air transport. Their constant occurrence, development, eastward movement and destruction is the main feature of the atmospheric circulation of temperate and adjacent latitudes, which is called cyclonic activity.

Rice. 65. Scheme of development of a frontal cyclone (according to S. P. Khromov)

Cyclones of temperate latitudes are huge flat ascending air eddies with a system of winds blowing counterclockwise in the northern hemisphere, and clockwise in the southern hemisphere and converging to their center. At the earth's surface, they are characterized by reduced pressure.

Cyclones are flat eddies: their horizontal dimensions reach 1000–3000 km (in diameter), while their vertical ones range from 2 to 10 km. Pressure in cyclones ranges from 1000 to 950 mb, winds can reach speeds of 25 m/s or more.

In their development, cyclones go through several stages - from nucleation to filling. Cyclones owe their formation to wave perturbations of the atmosphere at the fronts under the conditions of a rotating Earth, as a result of which the Coriolis force plays a significant role in this process. At the interface between air masses of different temperatures, warm air begins to penetrate into the cold air region and deviate from the sublatitudinal direction to high latitudes. The imbalance forces the cold air in the rear of the wave to penetrate into low latitudes. A cyclonic air movement develops, and a cyclonic bend of the front appears - a huge wave that begins to move from west to east (Fig. 65).

Different values ​​of the baric step in cold and warm air determine already at the initial stage of cyclone development a low pressure in its warm part, due to which warm air begins to rise and slide along the front surface in the front part of the wave. This is the first stage in the development of a cyclone - wave stage.

If the length of the newly arisen wave is 1000 km or more, then it turns out to be unstable in space and continues its development; in this case, the cyclone moves to the east at a speed of up to 100 km per day. The pressure continues to decrease, the winds increase, and the wave amplitude continues to increase, and the decrease in pressure propagates upward to a height of 5–6 km. The second is coming stage– young cyclone, at which it is usually outlined on surface pressure maps by several isobars.

When warm air moves to high latitudes, a warm front forms; when cold air moves towards the tropics, a cold front forms. Both of these fronts are conjugated in the center of the cyclone and are parts of a single whole, emphasizing the wave disturbance of the atmosphere. On satellite images, the fronts in cyclones are expressed as a continuous wide band of cloudiness in the warm front zone in the front part of the cyclone and in the center and a narrower band in the cold front zone in the rear part of the cyclone.

In a young cyclone, various parts are distinguished: Front edge in front of a warm front warm sector between two fronts rear part- behind the cold front (Fig. 66). At the main polar fronts, the warm sector is formed from tropical air, while the rest of the cyclone is formed from polar air. On the Arctic (Antarctic) front, the warm sector of the cyclone is formed from the polar air, and the rest of the cyclone is formed from the Arctic (Antarctic) air.

The cold front always moves faster than the warm front, so the warm sector of the cyclone is gradually reduced. When a cold front catches up with a warm front and merges with it, an occlusion front is formed. At the same time, warm air is forced upward and twists in a counterclockwise spiral in the northern hemisphere and clockwise in the southern hemisphere. The cyclone reaches the third stage of its development - occlusion. At the same time, the pressure in the cyclone drops to 980–960 hPa, the closed circulation extends to heights of more than 5 km, and the diameter reaches 1.5–2 thousand km.

Then comes the fourth (final) stage of cyclone development - its filling. The occlusion front gradually erodes, the warm air is finally pushed upwards and, at the same time, cools adiabatically. Cloud systems of filling cyclones take the form of twisted spirals. Temperature contrasts in the cyclone disappear, it becomes cold over its entire area and volume, slows down its movement and finally fills up. The entire life of a cyclone from inception to filling lasts 5–7 days.

Rice. 66. Cyclone of moderate latitudes in plan and its profiles. The names of the clouds are indicated in table 2

Cyclones are associated with cloudy weather, cool summers and warm in winter, and precipitation.

The emergence and development of frontal anticyclones is also associated with the development of cyclonic activity. Anticyclones are descending atmospheric vortices, comparable in size to cyclones, with a surface area of ​​high pressure, with an anticyclonic wind system from the center to the periphery clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. The emergence and development of anticyclones is closely related to the development of cyclones - this is a single process of evolution of the frontal zone. In other words, cyclones and anticyclones are paragenetic (i.e., closely related) formations.

Anticyclones form in the rear of the cold front of a young cyclone in cold air and also go through a series of stages. First comes young low cold anticyclone, very mobile, moving after the cyclone. Then comes the stage of maximum development: in this case, the anticyclone becomes high and sedentary. An inversion layer is formed in it, above which the air is quite warm due to adiabatic heating as it sinks, and below it is colder due to effective radiation, especially in winter over land. At this stage, the anticyclone is called a blocking anticyclone, since it prevents the western transfer of air masses up to high altitudes. Finally comes final stage of destruction when the airflow stops. Although anticyclones form during frontal zones ah, the front does not pass through them, but borders them on three sides. Cloudless dry weather, hot in summer and frosty in winter, is associated with anticyclones.

Rice. 67. A series of cyclones on the climate front, which are at different stages of development. 1–4 - stages of development of cyclones

Cyclones and anticyclones arise over zones of temperature and pressure contrasts. Therefore, extratropical cyclonic activity on the globe is carried out mainly on the main arctic (antarctic) and polar fronts, and the most active places of cyclogenesis are the zones of air encounters over cold and warm ocean currents. In the northern hemisphere, these are the convergence zones of the Labrador and Gulf Stream, Kuril and Kuroshio currents. In the southern hemisphere, the main place of cyclogenesis is the "roaring" (40 - 50 °) latitudes, where warm and cold air masses meet, especially where warm currents flow along the western margins of the oceans during the westerly winds.

At the same time, in winter, when the contrasts of temperatures and other properties of various air masses are maximum, cyclonic activity also manifests itself in other places. In particular, active cyclogenesis occurs at this time over the North, Mediterranean and Black seas, on the intramass polar front between warm sea and cold continental polar air.

Cyclones and anticyclones arise on climatic fronts one after the other, i.e. sequentially in time. The most typical picture is when series of cyclonic eddies of different ages are successively located on the arctic or polar front, which are at different stages of their development - from the youngest on the western edges of the fronts to filling up on the eastern ones (Fig. 67). Anticyclones appear in the same way.

Both cyclones and anticyclones (more precisely, their centers) move in temperate latitudes in the direction of the general air transfer from west to east, i.e., the movement of cyclones and anticyclones means their movement as a single system (with winds in different parts these vortices can have different directions). However, when moving eastward, cyclones deviate towards high latitudes, while anticyclones deviate towards the tropics.

The translational movement of cyclones in the northern hemisphere to the northeast (see Fig. 67) is partly due to the fact that the winds in them, blowing counterclockwise, in the southern peripheries are enhanced by western transfer and, as it were, push the cyclones to the north (Fig. 68, a). In the southern hemisphere, cyclones move to the southeast. There is also an opinion that the deviation of cyclones to high latitudes is facilitated by the intrusion of warm air into warm sectors, respectively, from the south in the northern hemisphere and from the north in the southern hemisphere.

Developing and moving, cyclones eventually reach the final stages, overtake each other and become inactive. At the same time, cyclones form one common deep vast area of ​​low pressure in the subarctic latitudes, which is called central cyclone. In the northern hemisphere, they form in the north of the Atlantic and Pacific oceans, where climate maps show such centers of atmospheric action as the Icelandic and Aleutian lows. Active cyclonic activity in winter in temperate latitudes and on the Arctic front in the region of the Barents and Kara Seas forms a deep baric trough there, extending from the Icelandic low. A second similar hollow extends from it to the Baffin Sea. The axes of the troughs coincide with warm currents.

Cyclones that arise on the intramass polar front between the Atlantic sea and continental polar air are displaced through Central Europe to the East European Plain and further to the north of Western Siberia. The path of winter cyclones of the Mediterranean branch of the polar front lies through the Balkan Peninsula, Ukraine, the central regions of European Russia and further to the northeast. These cyclones are associated with thaws and large amounts of precipitation in winter. The degree of manifestation of cyclogenesis is partly influenced by the orographic features of the continents: for example, in North America, the Cordilleras serve as a kind of barrier on the way of the North Pacific cyclones to the east.

In the southern hemisphere, cyclones form a low-pressure belt around Antarctica with a chain of isolated baric minima within it.

Thus, the baric minima of subpolar latitudes, which are especially pronounced in winter over the oceans and coincide with areas of positive temperature anomalies, are formed and maintained by cyclones coming here.

The deviation of anticyclones from temperate latitudes to the tropics can be explained by the fact that the winds in them, blowing clockwise in the northern hemisphere and counterclockwise in the southern hemisphere, are intensified by western transport at their polar margins, which gives the movement of anticyclones a meridian component (see Fig. 68 , b). In the northern hemisphere, anticyclones move to the southeast, in the southern hemisphere - to the northeast. Closing anticyclones, invading from temperate to subtropical latitudes, constantly regenerate and support areas there. high blood pressure– oceanic subtropical baric maxima: North Atlantic, North Pacific, South Atlantic, South Pacific and South Indian. Thus, all centers of action of the atmosphere - permanent and seasonal baric minima and maxima - have a complex - both thermal and dynamic origin.

Due to the meridional component frontal cyclones and anticyclones are involved in interlatitudinal exchange air from subtropics to subpolar latitudes. In this exchange, an important role is played by winds inside cyclones and anticyclones. Along the rear western periphery of anticyclones and the front eastern periphery of cyclones, they carry warm air masses from low latitudes towards the poles. Along the rear western periphery of cyclones and the front eastern periphery of anticyclones, cold air masses invade up to the tropics.

So the cyclones and anticyclones themselves, along with the winds along their periphery, carry out the exchange of air masses in the meridional direction. But the zonal component still prevails, which is expressed in the movement of cyclones and anticyclones in temperate and adjacent latitudes from west to east.

Other - monsoonal– circulation occurs in extratropical (primarily in temperate and subtropical) latitudes on the eastern coasts of the continents. Here, a sharp change in the prevailing direction of winds in winter and summer to the opposite is clearly expressed, which is associated with different seasonal heating of land and ocean and rearrangement, following the temperature, of pressure and changes in the position of the centers of action of the atmosphere in these latitudes. Such winds are called monsoons of extratropical latitudes (see fig. 64). Consider them on the example of the northern hemisphere. In summer, circulation here is determined by northward-shifting subtropical oceanic maxima and baric minima over the continents. Along the western peripheries of the North Atlantic and North Pacific highs, relatively warm maritime tropical and polar air masses move from the south and southeast to the heated continents - Asia and North America. This movement is carried out in the form of a series of cyclones that originate at the contact of sea and continental air and follow the direction of air flows to the north and northwest. With cyclones, masses of marine tropical or polar (depending on the latitude of the place) air, saturated with moisture, come to the continents, which pour out in the form of abundant monsoon rains, especially on the eastern slopes of the mountains and their foothills.

In winter, the circulation of air masses in these regions is determined by seasonal continental Canadian and Asian highs and pronounced Icelandic and Aleutian lows over the oceans. Steady northwestern winds bring dry and cold continental polar air from the continents to their eastern coasts, often reducing the temperature in winter to negative

values ​​even on the Great Plain of China. Chinese meteorologists have found that between the zones of equatorial tropical monsoons (with a frequency of more than 60%) and extra-tropical monsoons (with a frequency of less than 40%) there is a narrow band without monsoons. This testifies to the different nature of these monsoonal fields.

In North America, on the eastern coasts of extratropical latitudes, the monsoon circulation is weakened and the monsoon climate is almost not expressed.

Atmospheric circulation in high latitudes is peculiar. Here its thermal component is manifested, which is expressed in the predominance of winds eastern directions. Particularly well expressed southeastern winds along the outskirts of Antarctica; there they are amplified by the runoff effect (cold air flowing down from a high ice sheet) and blow steadily at speeds up to 20 m/s. stable in the northern hemisphere northeastern winds are observed only along the southern margin of Greenland, where they blow from the Greenland High to the Icelandic Low. In the high latitudes of Asia and North America the monsoon trend was noted in the atmospheric circulation (the frequency of winds is less than 40%). In winter, cold and dry southerly winds blow from the Asian and Canadian highs. In summer, the direction of the winds is reversed - they blow from the cold Arctic Ocean to the warmed land in the direction of thermal depressions over Siberia and Northern Canada. However, these winds do not give a monsoonal climatic effect, in particular, abundance and seasonality in the amount of precipitation.

Extratropical monsoons occupy an important place in the system of the general circulation of the atmosphere and in their regions. sustainable development render big influence on the climate.

In temperate latitudes, as a rule, the main weather changes are preceded by a series of pressure drops with high pressure areas wedged between them. Pressure reduction has for yachtsmen great importance: with a sharp drop in pressure, the wind usually increases to a storm and even with a small pressure difference changes its direction.

High pressure areas, or anticyclones, are areas where cold, dense air sinks and becomes warmer. They are usually much more stable than low pressure areas (see p. 265) and bring with them long periods of warm, dry weather in summer. In such areas, small clouds form, usually quite high, but clouds can be low, especially over the sea. Winds blowing in areas of high pressure are rather weak. The course of high pressure weather elements can be affected by the relief of the coast, if the wind blows on a hilly coast, or by sea breezes, the strength and direction of which change during the day (see p. 273).

Low pressure (cyclones)

The previous figure showed how an area of ​​low pressure first arises, and then a real cyclone develops from a small wedge in the polar front. It is clear that the weather that the observer sees and feels depends on his position relative to the center of low pressure. The closer to the center, the more severe the weather is likely to be.

Consider a typical cyclone passing somewhat to the north of the observer. The first signs are a drop in pressure (which the yacht's barometer will record) and the appearance of a thin high cirrus cloud. The greater the speed of the cirrus cloud and its density, the lower the pressure and the more likely it is that a gale will blow. Such thin high clouds warn the yachtsman of an impending storm in 12-24 hours, depending on how fast the cyclone is moving.

The cirrus cloud gradually becomes thicker and turns into a cirrostratus cloud that covers the sky at high altitude. The Sun or Moon has a halo (bright circles), the pressure drops and the direction of the wind changes counterclockwise: so, the west wind will change to the southwest or south-southwest. With a strong pressure drop, cirrostratus clouds become thicker and quickly become altostratus, but with a moderate change in pressure, the clouds look more as in photo 3 (see p. 263).

Gradually the cloud becomes thicker and nimbostratus clouds form.

Visibility deteriorates, the base of the cloud drops lower and heavy rain begins. The pressure continues to drop and the wind may move further south or even move into the southeast quarter. As the warm front passes, the rain turns to drizzle or stops altogether. The pressure usually stabilizes and the wind changes its direction again closer to the west. A sailor far enough from the center of the cyclone can see the cloud disintegrate.

cold fronts

As a cold front (which follows warm air masses) approaches, the pressure may begin to drop again (since the area of ​​low pressure - the "trough" - often precedes the front) and the wind will again turn slightly to the south. However, there will be very little visible signs of an approaching cold front, since the yacht will still be in the warm air sector.

When a cold front does arrive, it can spread very quickly.

The additional energy from the cold front changes the direction of the wind as cold air rushes down under the warm, causing it to rise quickly. This causes heavy downpours and is accompanied by gusts of wind and squalls. Warm air convection causes large cumulus clouds- shower clouds (see Figure 4 on p. 262). A characteristic feature of cold front clouds is that they move in the opposite direction to warm front clouds, but it is quite difficult to recognize them, since the front itself usually passes twice as fast.

As the cold front passes, the direction of the wind usually changes clockwise, often towards the northwest, and the pressure begins to rise. The clouds are dissipating and visibility is rapidly improving. The passage of a cold front closer to night gives a picture similar to that shown in Figure 5 (see p. 263), which confirms the old proverb “If the sun is red in the evening, the sailor has nothing to fear.” A high cloud that disappears with the onset of night almost always portends a beautiful weather, while high clouds appearing at dawn from the east, causing the sky to turn "red in the morning", are usually the precursors of a warm front and the associated decrease in pressure - "If it's red in the morning, the sailor is not comfortable."

Depending on the location of the yacht in relation to the area of ​​low pressure, various options for changing the weather and wind strength are possible. If the cyclone is very active, the wind shifts and the pressure drop increases. The propagation speed of the low pressure area can reach 30 m/s. Clouds will outpace the warm front by 960 km and rainfall by 160 km.

A powerful cyclone can cause a storm in the sea with strong winds and large waves. Signs foreshadowing such a situation are a rapid drop in pressure (by barometer) and the approach of a thin high cloud. In addition, storm warnings are broadcast by radio, and most yachts in coastal waters can take shelter in the harbor before the storm hits. For more information on the different types of storms, see p. 274, and on weather forecasting, p. 277. If the captain's forecast turns out to be wrong and the yacht is taken by a storm, you will be forced to storm on the high seas.

Diagram (see above) of prevailing wind directions and major ocean currents	On the left is a more detailed diagram of the directions of winds and currents in the North Atlantic.	Arrows indicate wind direction - blue for January, orange for July. The prevailing wind directions are indicated by thicker arrows. Dark red arrows - directions of the main currents

Winds are the movement of air currents under the influence of temperature and pressure differences. Cold heavy air masses descend to the surface of the earth, form areas of high pressure, and rising warm light air masses form areas of low pressure. Air currents moving from an area of ​​high pressure to an area of ​​low pressure are called wind.

At low latitudes (between the equator and 30° N and S), the Earth receives significantly more solar heat than at high latitudes (60-90° N and S). Temperature fluctuations complicate the movement of air masses, areas of high and low pressure appear, which cause characteristic winds around the globe. Approximately at latitudes of 30° north and south of the equator and above the poles, huge anticyclones are constantly formed, and at 60° N. sh. and yu. sh. and at the equator - areas of low pressure. Therefore, from 30 ° N. sh. and yu. sh. air masses move towards the equator, creating trade winds. Winds blowing in the direction of areas of low pressure, i.e. 60 ° N. sh. and yu. sh., called moderate western. Air masses moving from areas of high pressure over the poles are cold and are known as polar easters.

The rotation of the Earth also affects the direction of the winds. Winds of meridional directions in the Northern Hemisphere deviate to the right, in the Southern Hemisphere - to the left, i.e. northern winds blow from the northwestern quarter, and southern winds from the southeastern quarter. In the places where the winds meet, mobile interfaces are formed, called fronts (see p. 268).

When the northeast and southeast trade winds meet, the so-called intertropical front arises. Since yachting is most widespread in temperate latitudes, yachtsmen must acquire knowledge of the meteorology of these latitudes.

Tropical meteorology (related to the intertropical front) has its own specifics. The meteorology of temperate latitudes is not applicable here. Although the formation of cyclones around the equator is similar, the direction of the winds does not always follow the rotation rules discussed earlier. Decisive importance belongs to local winds - the causes of frequent thunderstorms.

The figures show the prevailing wind directions over the oceans in January and July. Certain areas are well known in the Atlantic and Pacific Oceans where anticyclones are born, which are pronounced in northern waters and less definite in southern ones. In the Atlantic, these winds cause such currents as the Gulf Stream, the Canary and the North Trade Wind. A similar picture can be observed in the North Pacific Ocean, where similar winds create the Kuroshio and North Pacific currents. These currents, under the influence of the land areas flowing around them and the rotation of the Earth, change their direction clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

The figures show a diagram of the main directions of the winds. However, it must be refined depending on local pressure systems, coastal topography, and breezes that change their direction during the day.

weather systems

It was mentioned above that cyclones affect the weather. Now let's try to figure out how areas of high and low pressure change the prevailing wind directions. Mapped lines of equal pressure (isobars) form concentric figures around the centers of high and low pressure areas. Air masses tend to move directly from areas of high to areas of low pressure. However, due to the rotation of the Earth, air currents move tangentially to the isobars. In the Northern Hemisphere, winds deviate counterclockwise from an area of ​​low pressure and clockwise from an area of ​​high pressure. In the Southern Hemisphere, the movement is reversed.

There is a simple rule for determining the position of areas of high and low pressure. If you stand with your back to the wind in the Northern Hemisphere, the area of ​​low pressure will be on the left, and the area of ​​high pressure on the right, and vice versa - in the Southern Hemisphere.

However, this rule is valid at a height of 7 km above the earth's surface for the wind, which is called gradient. Near the surface, the direction and speed of the wind of interest to the yachtsman is distorted. Here, the direction of the wind deviates inward - towards the center of the cyclone, and with an anticyclone - outward - from its center. The deflection angle depends on the surface topography. Over the sea it is approximately 15°, and over land - 30°. In addition, gusts of wind with speed and direction are possible, which are typical for a height of 7 km.

local winds

The yachtsman must know not only the prevailing wind directions, but also, which is especially important for those who sail dinghies, the directions of local winds. Local winds also result from temperature differences. Air masses are heated directly from the surface over which they move, and not from the sun, as yachtsmen often believe. Depending on the speed and time of heating of various surfaces, the temperatures of the air masses above them will also be different, and this, in turn, determines the direction of the wind.

The most common local winds are sea breezes. The morning sun heats the earth, and the earth gives off heat to the air. Over the sea, the air masses are colder, since the water, absorbing the sun's rays, does not heat up as quickly as the land. When warm air masses rise over land, colder air from the sea rushes in to take their place. This wind is called the sea breeze. On a hot summer day, the sea breeze can blow many miles inland (until mid-afternoon). In the early morning, you can witness the calm, and later a breeze begins to blow - the wind towards the coast.

The opposite happens at night. At what rate the land heats up during the day, at the same rate it gives off heat at night. Usually the temperature of the Earth's surface drops below the temperature of the sea, and this leads to a light night (shore) breeze - a wind from the land, caused by the fact that the air masses over the land cool down and move towards the sea. If there are hills or mountains on the coast, the cold air rushes down under the influence of gravity, causing a strong wind blowing down the slope, which is called downslope. Sometimes the speed of this wind is such that its energy is enough for several miles from the coast. Most often, a downward wind blows at night at the same time as a light coastal breeze.

On domestic waterways- lakes or rivers - the same principles of the emergence and movement of winds apply. The air above the land heats up, rises, allowing the colder air above the water to move away from the river. When sailing on a dinghy, you can achieve good results, given the direction of these light winds.

A novice yachtsman will immediately notice that obstacles on the coast affect the speed of the wind. Obviously, a moored large vessel creates a dead zone on the leeward side. Moorings, boat storage sheds and warehouses also restrict air movement. Trees along the coast line can cut wind speed by almost half. Therefore, one must go either close to the trees, where the wind blows through them, or as far as possible from the trees, so that they do not affect the wind speed.

It must always be remembered that the wind speed on land and at sea is different. It decreases significantly on contact with the ground, and in a yacht club or anchorage, a strong wind can often seem like a light breeze. However, using the Beaufort scale, you can correctly determine the wind speed even on land. And, of course, the accumulated experience will help to approximately estimate the real strength of the wind in the sea.

Masses of warm air rise above the ground and colder air from the sea rushes in to take their place. This landward wind is known as the daytime (sea) breeze.	Cold air from the mountains descends along the slope and displaces the warm air rising over the sea. It is called the night (coastal) breeze (in some areas - bora)	On a river or lake, warm air rising above the shore is displaced by cold air from the surface of the water. These local winds can be used by dinghy sailors.

The main features of the Russian climate are determined by a number of geographical factors. Among the most important of them is solar radiation, which depends on geographic latitude. In general, Russia is located mainly in high and middle latitudes. That's why the climate in most of our country is harsh, with a clear change of seasons and a long winter.

The significant length of the country from north to south leads to climate change depending on the latitude of the place where solar heat is received - total solar radiation. In the Arctic, the annual amount of total solar radiation is 251.2 kJ/cm 2 per year, in the subarctic - about 293 kJ/cm 2 per year. In the temperate zone, due to its large extent from north to south, the total solar radiation varies from 293 kJ/cm 2 per year in the northern part to 544 kJ/cm 2 per year in the southern part. In the subtropics, the total solar radiation increases from 544 to 670 kJ/cm2 per year.

Throughout Russia, there is a very large difference in the seasonal supply of solar heat. It depends both on the change in the angle of incidence sun rays by seasons, and by the length of time of sunshine. The seasonality of all natural phenomena is associated with differences in the inflow of solar heat.

Oceans have a huge impact on the climate of Russia. The role of the Atlantic Ocean is the greatest, despite the fact that its waters do not directly wash the territory of the country anywhere. In temperate latitudes, in which most of our country is located, as is known, the western transfer of air masses dominates. In addition, in the west of Russia there is no high mountains that prevent air transfer. As a result, the influence of the Atlantic extends very far, up to the Verkhoyansk and Transbaikal ridges. Sea air masses of temperate latitudes spread with western transport. In winter, they cause a softening of frosts up to thaws in the western regions, bring snowfalls. In summer, the arrival of the Atlantic masses is accompanied by cooling and precipitation.

The climate-forming influence of the Arctic Ocean is very great. Over the arctic cold basin throughout the year there is an area of ​​increased atmospheric pressure. From here, the Arctic air, gradually transforming, spreads over the entire territory of Russia in summer. The slope of the largest plains of the country to the north contributes to the penetration of Arctic air far to the south. The impact of the Arctic air is especially pronounced on the territory of the East European Plain. In winter, the arctic air causes a sharp cooling here. Moving south, it warms up relatively and dries up. Frosty sunny days without snowfall. In summer, Arctic air initially causes cooling, and then it heats up and forms cloudless or partly cloudy weather. The arrival of arctic air on the territory of the European part of Russia in early spring is accompanied by a return of cold weather and is dangerous for many cultivated plants, as it causes frosts. Most often they are in May. Droughts in the Volga region and in the south of Western Siberia are associated with the invasion of the Arctic air.

The Pacific Ocean has some influence on the climate of Russia. Despite its enormous size, its impact is limited to a relatively narrow strip of land along the Far Eastern seas. This is due to the fact that the ocean is located to the east of our country, over which the western transfer of air masses dominates in temperate latitudes. High mountains along the coasts also prevent Pacific air masses from penetrating deep into the country - site. In winter, an area of ​​high atmospheric pressure (Asian High) forms over the cold surface of the continent, from where the air rushes towards the relatively heated ocean (winter monsoon). The influence of the air masses of the Pacific Ocean is clearly visible only in summer. At this time, there is a high pressure area over the ocean, and low pressure over land. As a result, there is a movement of sea air masses to land in the form of a summer monsoon.

Among the climate-forming factors is the nature of the underlying surface. In the conditions of our country, these are, first of all, features of the relief. In winter, other differences in the nature of the underlying surface are offset by snow cover. The relief also affects the climate throughout the year.

The most important climate-forming properties of the relief are flatness of the territory. On the plains of the European part and Western Siberia, the air of the Atlantic penetrates far to the east. Moving away from the ocean, the air gradually transforms and turns into continental. Thus, the continentality of the climate gradually increases from west to east. The low Ural Mountains are not an obstacle to the spread of Atlantic air from the west.

The adjacent plains of Western Siberia contribute to the penetration of arctic air masses far to the south. The high mountains of the south of our country - the Caucasus, Kopetdag, Tien Shan and Pamir prevent further movement of air masses to the south from the north. Thanks to their protection, along the southern borders of the Caspian there are territories with a subtropical climate.

In the temperate zone, within which most of the territory of Russia is located, the seasons are clearly expressed. The most severe season in most of our country is winter. In temperate and high latitudes, the radiation balance at this time of the year is negative. Only in the extreme south does it have a positive meaning.

The earth's surface becomes very cold in winter and cools the lower layers of air. This process is especially intensive over the regions of Eastern Siberia, remote from the oceans. In the north-east of Siberia, in the intermountain basins, the average January temperatures drop below -40 ° C, in the Oymyakon region to -48 -50 ° C. An area of ​​high pressure is formed here, which extends to the whole of Siberia and gives two spurs. One spur grows to the northeast to Chukotka, and the second - to the southwest through the south of Western Siberia and the Volga Upland to the lower reaches of the Dniester.

In the interior regions of Siberia, within the area of ​​high pressure, descending air currents dominate in winter. Therefore, windless, slightly cloudy frosty weather is established. Calmness and great dryness of the air make it easier to endure frosts and adapt to them.

In winter, air pressure over Russia is increased, and over the surrounding seas and oceans it is reduced. Therefore, the spreading of air from the territory of the country towards the oceans dominates, with the exception of the European part of the country. On the coasts of the Pacific seas, northwestern winds (winter monsoon) dominate in winter, which carry cold, dry air from continental Siberia. In this regard, in almost all regions of the Far East, winters are cold and snowy. In Vladivostok, which is located at the latitude of Sochi, the average January temperature is -12°C, and in Sochi +6°C. Over the coasts of Kamchatka and Sakhalin Island, where continental and maritime air masses collide, frontal processes occur, which are often accompanied by heavy winds and heavy snowfalls.

On the coasts of the seas of the Arctic Ocean, southwestern and southern winds dominate in winter, which carry continental air of temperate latitudes to the north, flowing from the Asian High. Along the margins of the northern seas, it meets the arctic air, as a result of which the arctic front arises. This front is most pronounced over the Sea of ​​Okhotsk and the Barents Sea, where it causes frequent and severe storms and fogs.

Over the plains Central Asia and the south of the European part of the country, northeast winds dominate. They are caused by the outflow of air masses to the south from the spur of the high pressure area. Since the air moves from the northeast, it brings cooling and relative dryness to the southern regions of the country, so little snow falls here, and in harsh winters the Sea of ​​Azov and the northern parts of the Caspian and Black Seas freeze.

In central and northern parts The East European Plain north of the high pressure spur is dominated by western air currents from the Atlantic Ocean. These air masses always bring moisture in the form of snow or rain. But their temperatures are different. If the southwestern winds bring thaws in winter, the northwestern winds bring relatively cold air from the regions of the North Atlantic and Scandinavia.

Over most of the European Plain, a large number of cyclones move during the winter. They arise along the polar front passing to the west of our country over the North Sea. From here, cyclones move east, passing over Western and Eastern Europe. Space and ground control over their movement makes it possible to predict the weather on the territory of the European part of the country.

During the interaction of continental and sea air masses of temperate latitudes, a polar front often forms in the central part of the East European Plain. In the rear of the cyclones crossing the plain from west to east, cold arctic air masses flow southward. Thus, over the territory of the East European Plain there is an intense interaction between the Atlantic and Arctic air masses, sea and continental air of temperate latitudes. Therefore, the weather here is most often unstable and very contrasty, with frequent changes of cold and thaw. Within a few hours, the air temperature in winter can change from a few degrees of heat to 21-24 degrees of frost, and the rain can be replaced by snow. Such a change is accompanied by thaws and ice, which have an extremely unfavorable effect on the economic activity of people - site. Transport suffers from ice; thaws can lead to the death of winter crops. The alternation of frosts and thaws leads to the destruction of roads and various structures. Intense cyclonic activity also leads to dissimilarity of winter weather in different years.

Warm Atlantic air masses, moving to the east, gradually cool down. Therefore, the isotherms over the European territory of Russia have a meridional direction. Above Eastern Siberia isotherms have a closed annular character, reflecting the continentality of the climate of this territory. The Pacific Ocean has a less warming effect on the continent compared to the Atlantic. Therefore, on the coast of the Pacific Ocean, isotherms are located meridional only within a narrow strip. Over the southern regions of the country, the isotherms extend latitudinally in accordance with the direction of change in the value of total solar radiation and the radiation balance.

In most parts of Russia, precipitation falls in winter in the form of snow. In the North Caucasus, the thickness of the snow cover usually does not exceed 10 cm; in the Kaliningrad region, in the Volga region - up to 10-30 cm. In the north of the European Plain, north-east of Western Siberia, on Sakhalin - 80-90 cm, and on the eastern coast of Kamchatka, the thickness of the snow cover reaches 120-160 cm. The duration of the snow cover is also very different - from several days in a number of regions of the Caspian Sea to 260 days in Taimyr.

Snow is of great importance for natural processes and economic activities in our country.. It creates moisture reserves that are used by plants in spring and early summer. Thanks to the snow in the European part of the country, it is possible to grow winter crops. In spring, most rivers experience floods due to snowmelt.

In summer, the radiation balance is positive throughout Russia. The continent heats up more than the oceans, and an area of ​​low pressure is established above it. At the same time, areas of increased pressure are growing over the oceans: the North Atlantic (Azores) and North Pacific (Hawaiian) maxima. Increased pressure continues to exist over the Arctic Ocean (Arctic High). From these highs, air currents rush to the continent. The flow of sea air is most clearly expressed on Far East, where the southeasterly air transport is established in summer - the summer monsoon. Here the colder and therefore heavier sea air interacts with the continental air. As a result, frontal processes arise, with the passage of which heavy showers (monsoon rains) are associated on Sakhalin, Kamchatka, in the Khabarovsk and Primorsky Territories. Quite often, powerful cyclones come here in the form of typhoons that occur on tropical fronts outside our country. Monsoon rains are accompanied by flooding on the rivers. Floods are often catastrophic, especially in the basins of the Amur and Ussuri rivers, on Sakhalin Island.

In the north of Russia, Arctic air masses rush south towards warmer land. Over the northern seas, they meet with the air of temperate latitudes. The result is an arctic front. It is especially pronounced over the Barents Sea, since the most contrasting air masses interact over this relatively warm basin. The passage of the Arctic front over the northern seas is accompanied by storms and fogs.

Air from the north moves far to the south over the plains of Western Siberia. To the south of Central Asia, over the territory of Pakistan and Afghanistan, there is a center of low pressure (South Asian low), to which the northern air currents rush. Moving to the south, the arctic air warms up, dries up and gradually transforms into the continental air of temperate latitudes. Over the plains of Central Asia, it is very dry and forms a desert climate.

To the west of Russia, the Azores High grows over the Atlantic Ocean in summer, the spur of which runs over the East European Plain through southern Ukraine and the southern Volga region to the Ural River. To the south of it, the outflowing air masses warm up and dry out. Therefore, in the Sea of ​​\u200b\u200bAzov, and especially in the Caspian Sea, it is very hot and dry in summer. Irrigation is necessary to obtain sustainable crop yields here.

The flow of sea air from the Atlantic in the central regions of the European Plain interacts with continental air. As a result, a polar front is formed in the space from the middle reaches of the Dniester to the middle reaches of the Volga. All this is accompanied by intensive passage of cyclones. Therefore, in most of the European territory of Russia, the weather in summer, as well as in winter, differs from other territories of the country by great instability. In summer, heavy rains and cold spells often occur. Thus, the average monthly July temperature in Moscow is about +18°С, however, in some years it dropped to +5...+10°С or rose to +30...+34°С. To the east of the Volga, and especially beyond the Urals, the influence of maritime air masses is sharply reduced, and here the weather is usually dry and hot in summer.

In contrast to the winter season, summer isotherms stretch almost throughout Russia from west to east. This is due to the fact that in summer solar radiation is very high and it plays a major role in determining the temperature regime.

The summer season has the maximum amount of precipitation. This is due to high temperatures and therefore the maximum humidity of the local air, from which precipitation falls when it interacts with relatively cold air masses coming from the oceans. Precipitation of convective origin is added to them. The greatest amount of precipitation falls in the extreme western and eastern regions of Russia. With the distance from the oceans to the interior of the country, the amount of precipitation decreases, reaching its minimum (less than 50 mm). On the windward slopes of the mountains, the amount of precipitation increases significantly. Especially a lot of them falls on the western slopes of the Caucasus Mountains (over 2000 mm).

Extratropical monsoons are common in areas of the eastern coasts of the continents in temperate latitudes. During the summer monsoon, winds blow from the ocean to the mainland, in winter - from the mainland to the ocean, which is due to the difference in heating and cooling of the continents and oceans during the year and the distribution of air pressure associated with this. An area of ​​low pressure is established over land in summer, and an area of ​​high pressure is established over the oceans; on the contrary, over the oceans: high pressure prevails in summer, low pressure prevails in winter, which determines the direction of the winds of the summer and winter monsoons. Extratropical monsoons are well pronounced in the Far East of Russia, in China, Japan In these areas, the winter northwest monsoon is formed under the influence of the Asian anticyclone, which contributes to the removal of cold dry air from Siberia to the eastern coast of the Asian continent.Therefore, in Vladivostok, located at the latitude of Sochi, it is colder in winter than in Arkhangelsk. The monsoon brings here from the ocean and the Sea of ​​Japan moist cool air with a lot of precipitation and frequent fogs.

An important factor in the interlatitudinal energy exchange is tropical cyclones, which differ from extratropical cyclones in their smaller size (usually 400-600 km across, rarely up to 1000 km), large air pressure drops between the periphery and the center and, consequently, large horizontal pressure gradients, large wind speeds (25-30 m/s, speeds of 50-100 m/s were noted), heavy rainfall with heavy thunderstorms. Essentially, the entire tropical cyclone is a continuous thundercloud. Only in the very center of it is an area with a diameter of several tens of kilometers, in which clear, calm weather is the “eye of the storm”.

Cyclones originate in the tropical zone over the oceans at latitudes from 0 to 20° in both hemispheres. The conditions for their formation are a high temperature on the ocean surface (not lower than 27 °C) and high air humidity, which provides a large air instability energy necessary for the development of a cyclone.

Tropical cyclones that occur in eastern Asia are called typhoons, in the Indian Ocean - orcans, in the Atlantic Ocean - hurricanes.

On fig. 2.9 shows the path of movement of tropical cyclones. Originating in the tropics, cyclones move northwest to high latitudes at a speed of 10-15 km/h. Moving to temperate latitudes, they change their direction of movement to the northeast, while their speed increases. When they make landfall, tropical cyclones quickly fade, but at the same time they have time to bring huge destruction associated with strong winds and floods. When moving to higher latitudes over water, the cyclone acquires the properties of an extratropical cyclone and also fades. Sometimes Pacific typhoons reach Kamchatka.

On the globe, on average, from 80 to 120 tropical cyclones occur per year.

An important component of the general circulation of the atmosphere are jet streams, which are relatively narrow air flows with an almost horizontal axis, characterized by large horizontal and vertical wind shears (velocity gradients, i.e. changes in speed per unit distance).

The length of the jet streams is thousands of kilometers (sometimes encircling the globe), the width is several hundred, and the thickness is several kilometers.

The lower speed limit for the jet stream is 30 m/s, maximum speeds along the axis can reach 50 and 100 m/s, and velocities of 200 m/s (720 km/h) have been observed.

Jet streams are tropospheric and stratospheric. Tropospheric, in turn, are subdivided into jet streams of temperate latitudes, subtropical and equatorial.

Jet streams of temperate latitudes are formed in the area of ​​high-altitude frontal zones, which are a transitional layer between warm and cold air with large temperature and pressure gradients, and also cause high geostrophic wind speeds. They are located at an altitude of 8-10 km in winter and 9-12 km in summer. In the zone of tropospheric jet streams, the tropopause abruptly increases from high to low latitudes.

Tropospheric jet streams, being an integral part of the western transport, have a direction from west to east.

Stratospheric jet streams are observed at altitudes of 25-30 km with wind speeds up to 200 km/h. From season to season (summer-winter) they reverse direction. There are stratospheric jet streams at altitudes up to 60 km.

Jet currents carry various impurities around the globe: decay products of radioactive substances, dust particles, volcanic ash. They are of particular importance for aviation.

All considered types of atmospheric circulation that are part of the general circulation (trade winds, tropical and extratropical monsoons, westerly and eastern winds, tropical cyclones, extratropical cyclones and anticyclones, jet streams) ensure the exchange of air masses between oceans and continents, between high and low latitudes, the transfer of moisture from the oceans to the continents.

Intrazonal exchange occurs mainly due to air flows at heights along the parallels (quasi-geostrophic wind), interlatitudinal exchange - due to the meridional component in the surface layer, and in temperate latitudes - mainly due to cyclones and anticyclones.

Cyclonic activity is also the cause of interdiurnal weather variability.

local winds. Local wind is the wind in a certain limited area, which has characteristic features associated with the geography of the area. It can be: a manifestation of local circulation, independent of the general circulation of the atmosphere (breezes, mountain-valley winds); the result of the influence of local topography on the currents of the general circulation of the atmosphere (foehn, bora, etc.); manifestation of convection, sometimes vortex character ( dust storm); the course of the general circulation with such special properties for the given region as dryness, dustiness, low temperature, etc. (Afghan, Khamsin).

Breezes. Breezes are called winds that occur near coastline seas and other large bodies of water and having a distinct diurnal change of direction. During the day, the wind blows from the sea to the land - this is a sea breeze, and at night from land to sea - a coastal breeze (Fig. 2.10). The reason for the breeze is the difference in air temperature over the sea and over land, as a result of which a closed thermal circulation occurs. Sea breezes are usually stronger than land breezes. This is due to the fact that the temperature difference between the sea and land during the day is greater than at night. That is why sea breezes penetrate deep into the land for tens of kilometers and have a speed of 4-6 m/s, and coastal breezes at a speed of 3-4 m/s penetrate deep into the sea for 8-10 km.

Breeze circulation is more pronounced in tropical regions, especially on the coasts of the seas bordering deserts.

Slope winds, like mountain-valley winds, are observed in many mountainous areas; they blow along the slopes upward during the day and downward at night (Fig. 2.11). Like breezes, they have a daily periodicity. During the day, air adjacent to the slope of a mountain or valley heats up more than air at the same height, but far from the slope. Warm air rises up the slope and sucks in air from the valley, and air from the free atmosphere descends to replace it. Circulation is formed. At night, when the slopes cool, reverse circulation occurs.

Mountain-valley winds arise in large deep valleys overlooking the plains. During the day the wind blows up the valley, and at night from the mountains - down to the plain. At a certain height, the wind reverses direction. The vertical length of mountain-valley winds ranges from tens to several hundred meters.

Glacial winds blow along the direction of the glaciers. These winds arise when the air adjacent to the surface of the glacier cools and during the day remain colder than the air above the narrowing slopes. These winds reach their greatest strength during the day, when there is a great contrast between air temperatures above the glacier and in the free atmosphere. The height of the layer of glacial winds is from tens to hundreds of meters.

The most clearly considered winds of thermal origin are manifested in anticyclones, when they are not affected by large-scale atmospheric disturbances.

Local winds can also arise due to mechanical perturbations of air currents by the terrain. These winds include foehn and bora.

Föhn is a dry and hot wind blowing from high mountains into a valley or sea. This wind occurs if the path of the air flow meets across the located mountain range. Let there be a mountain range 3 km high on the path of the air flow and the air temperature at its foot on the windward side is 20 ° C (Fig. 2.12). Assume that the level of condensation is at an altitude of 1.3 km. The surface flow, having encountered an obstacle, will begin to rise along the slope of the ridge and cool adiabatically until it reaches the level of condensation; its cooling will occur according to the dry adiabatic law with a vertical temperature gradient of 1 °C per 100 m of ascent. As it rises further above the condensation level, water vapor will begin to condense, forming clouds with precipitation. The drop in air temperature from the condensation level to maximum height rise (up to 3 km) will occur according to the humid-adiabatic law with a temperature gradient of 0.5 ° C per 100 m of altitude.

Under the influence of dynamic pressure, part of the air, having reached the top of the ridge, will then begin to descend to the lee foot of the ridge and heat up. Heating will occur according to the dry adiabatic law with a temperature gradient of 1 °C per 100 m of altitude, as a result of which the air temperature will rise at the foot of the ridge to 28.5 °C.

An increase in temperature is accompanied by a decrease relative humidity air. Changes in temperature and air humidity with a hair dryer can be quick and abrupt: in 1-2 hours the temperature can rise by 30-40 °C. The duration of the hair dryer ranges from several hours to 5 days or more. The wind speed with a foehn ranges from small values ​​up to 15-20 m/s, and sometimes reaches 30-40 m/s.

Hair dryers are observed in all mountain systems peace. In winter, the foehn can lead to snowfalls in the mountains, in spring and summer - to the rapid melting of snow in the mountains and spills mountain rivers. In summer, due to high dryness and temperature, it can have a detrimental effect on vegetation.

Dry wind - wind at temperatures above 25 ° C (often up to 35-40 ° C), relative air humidity less than 30%, a large saturation deficit, having speeds above 5 m / s (often up to 20 m / s), is observed in summer in the steppe , forest-steppe zones of the European territory of Russia, especially in Caspian lowland, as well as in Kazakhstan and Central Asia.

Dry winds are formed as a result of the transformation of air masses, most often of arctic origin. Arctic air invades from the north along the east
periphery of the anticyclone, having low temperature and absolute humidity. Moving over the continent to low latitudes, it warms up strongly and becomes even drier. Continuing its path along the southern and southwestern periphery of the anticyclone, the Arctic air enters the above areas already hot and dry. The formation of dry winds is also influenced by the downward movement of air in the central part of the anticyclone, which contributes to the heating of the air and a decrease in its humidity.

In the southeast of the European part of Russia, dry winds can be observed from April to September, especially often in the Caspian lowland. In the Saratov-Astrakhan region during this period there are 40-80 days with dry winds, and in the Central Asian deserts - up to 180 days.

Dry wind - one of the most unfavorable for agriculture meteorological phenomena. High temperature, low humidity and significant wind speed lead to intensive evaporation of moisture from the soil, transpiration by plants and, as a result, to drought. Under such conditions, plants dry out even with a sufficient supply of moisture in the soil, since their root system does not have time to supply enough water to the ground part.

Hot winds, similar to dry winds, are observed in tropical and subtropical regions and have local names.

Samum is a local wind in the deserts of Arabia and North Africa, which has the character of a squall with a strong sandy; storm, often with a thunderstorm.

Khamsin - a dry and hot wind of southern directions in northeast Africa, especially frequent in the spring months, carries dust and sand in large quantities, greatly reducing visibility.

Sirocco is the Italian name for warm and humid winds, in Arabia and Palestine and Mesopotamia, winds of this type are very dry and carry clouds of sandy dust.

Bora - strong, cold and gusty wind blowing from low mountain ranges to the side warm sea. It is formed mainly in the cold season, when a high-pressure area is established over a cold continent, and a low-pressure area is established over a warm reservoir. At the same time, cold air begins to move towards the sea. If a mountain range is encountered on its way, then the air tends to cross it at the lowest height, so it most often moves through the passes. In this case, the air flow narrows, which leads to an increase in its speed. In view of the relatively low height of the pass, the adiabatic heating of the descending air during the bora is insignificant.

Bora has long been known in the region of the Novorossiysk Bay and on the Adriatic coast. For a year in Novorossiysk there are 46 days with bora. Wind speed up to 60 m/s, air temperature decrease - by 25°С and more. The Novorossiysk bora dies out in the sea already a few kilometers from the coast. The duration of the bora is 1-3 days. Bora is also found on Novaya Zemlya in the Arctic. In France, the local name for bora is mistral. ^

In Greenland and especially in Antarctica, katabatic winds are observed - this is the movement of cooled air under the action of force, gravity along a rather long gentle slope.

In Antarctica, a high ice plateau contributes to the formation of a powerful anticyclone over the ice dome and the flow of chilled air. The katabatic winds are especially strong in those parts of Antarctica where the ice slope is rather steep or where there are glacial valleys coinciding with the direction of the runoff. Wind speed increases towards the coast and near the coast reaches 20 m/s, speeds of 45 m/s with gusts up to 90 m/s were noted.

Squalls are sharp short-term increases in wind in limited areas. In most cases, squalls are formed during the passage of cumulonimbus clouds of local convection or a cold front. Wind speed of 20 m/s or more.

Under conditions of great instability of atmospheric stratification, in addition to thunderstorm squalls, special vortices with a vertical axis can also arise. These are very small dusty whirlwinds, which in many cases arise above overheated soil in deserts (but not only in deserts), especially at the boundaries * where the properties of the underlying surface change dramatically. In the Sahara Desert, on an area of ​​10 sq. km, up to 100 such eddies are sometimes observed per day.

A tornado is a vortex with a vertical axis that occurs during a squall or thunderstorm and has a very high rotation speed. Connecting the cloud to the ground or water, it moves at a considerable speed and has great destructive power. A tornado over land is called a thrombus, in America it is called a tornado. The diameter of a tornado over water is about 100 m, over land - up to 1000 m. The height is about 1 km. By the nature of the destruction, it was possible to establish that the speed of air movement in these vortices is 50–100 m/s, and in especially intense tornadoes it reaches 250 m/s, and there is a large vertical component of the velocity equal to 70–90 m/s. There is very low pressure inside the vortex.

5. OCEANIC CURRENTS

Of particular importance for climate formation is the interaction between the ocean and the atmosphere, which manifests itself in the exchange of heat, moisture, and momentum. The ocean is a huge accumulator of solar heat and moisture. Thanks to him, sharp fluctuations in temperature are smoothed out on Earth and remote areas of land are moistened.

Oceanic circulation, which occurs mainly under the influence of atmospheric circulation, plays an important role in interlatitudinal heat transfer. It has been established that about half of the total advective heat transfer from low latitudes to high latitudes and from high latitudes to low latitudes is carried out by ocean currents, and the remaining half - through atmospheric circulation.

Ocean currents primarily affect air temperature, its distribution and temperature stratification of air masses. Cold currents increase the stability of the atmosphere and thereby weaken the vertical exchange of air and water vapor. Therefore, the frequency of fogs increases, cloudiness and precipitation decrease, which contributes to the maintenance of coastal deserts.

Warm currents, on the contrary, contribute to the development of thermal convection in the atmosphere and, consequently, air humidification to significant heights. Especially great is the instability of air over warm currents in winter time, which often leads to winter thunderstorms even in areas as far north as the coast of Norway. Zones of increased precipitation are usually confined to warm currents. The scheme of currents of the World Ocean is shown in fig. 2.13.

Currents in the latitudinal direction are neutral, since they do not participate in the interlatitudinal heat transfer (these include the northern trade wind, southern trade wind, equatorial countercurrent, etc.).

Currents from the tropical belt to the south or north are warm, and currents directed from high latitudes to low latitudes are cold. For example, through the strait between Florida and Cuba, a powerful warm Florida current emerges from the Gulf of Mexico, which gives rise to the Gulf Stream system with temperatures above 28 ° C. The greatest width of this stream is 120 km, depth - 2 km, length - 10 thousand km, water flow is 9-10 10 m 3 /h. This stream carries 22 times more water than all rivers the globe.

Crossing the Atlantic Ocean, the Gulf Stream heads northeast and splits into several streams. It brings a huge amount of heat to the shores of Western Europe, where, washing the coast of Norway, it penetrates into the Barents Sea to Svalbard, significantly warming the western sector of the Arctic.

A large cold current from the Baffin Sea - the Labrador Sea - heads south, when it meets the Gulf Stream, the Subpolar Hydrological Front is formed. This is where cyclones often originate.

In the southern hemisphere, in the zone of western transport, a powerful current of western winds operates. From the high latitudes of the southern hemisphere, the cold Peruvian Current passes along the western coasts of South America, and the cold California Current flows along the western coasts of North America. Large oceanic circulations also exist in other areas of the World Ocean.

Cold currents coming from high latitudes contribute to the cooling of the tropics. Warm currents from tropical regions warm the high latitudes. Ocean currents, arising under the influence of atmospheric circulation, affect atmospheric circulation.

For recent decades Of great practical and scientific interest to climatologists is the El Niño phenomenon, which is expressed in an anomalous increase in the temperature of the surface waters of the Pacific Ocean off the western coast South America during the summer months. The reason for this phenomenon is not fully understood, but it has been established that an increase in the intensity of El Niño is noted in years of weakening trade winds and changes in other air currents.

The intensity of El Niño manifests itself with some periodicity. So, in 1982, the anomaly of the surface temperature of the Pacific Ocean spread over vast areas and amounted to 6 C.

During the El Niño years, west coast South America has experienced catastrophic downpours - even in areas where there has been no rain for many years before, such as the Atacama Desert.

El Niño, being a product of disturbances in the general circulation of the atmosphere, itself has an impact on cyclonic activity in global areas, causing abnormal weather phenomena, floods in some areas and droughts in others, as well as the formation of tornadoes and tornadoes.

The arrival of El Niño pushes the cold Peruvian Current away from the coasts of Peru and Chile, preventing the rise of deep cold waters. The influx of warm waters into this area with a low oxygen content has a detrimental effect on vegetable world and living organisms, which adversely affects the economies of coastal countries for which fishing is important.

Thus, ocean currents are a powerful climate-forming factor that influences the climate of vast areas through atmospheric circulation.

6. THE ROLE OF RELIEF IN THE FORMATION OF CLIMATE

The relief has a great influence on the climate, especially large landforms - mountains. In the mountains, a special type of climate is created, called the mountain climate.

In mountains with height, due to a decrease in the air mass located above and an increase in its transparency, the influx of solar radiation increases. The proportion of short-wave radiation is greatly increased. However, the increase in solar radiation does not compensate for the heat loss as a result of intense effective radiation. For this reason, and also under the influence of adiabatic cooling, the air temperature decreases with height. However, with the formation of temperature inversions in winter, the air temperature can increase to a certain height. The occurrence of such inversions is promoted by hollows, where cold air rolls down. So, in Verkhoyansk (altitude 120 m) the average February temperature is -46.8 °C, and in Semenovsky Rudnik, located in the Verkhoyansk ridge at an altitude of 1020 m, the temperature is -30.5 °C.

The daily and annual amplitudes of air temperature decrease with height. There is a delay in the onset of annual maximum and minimum temperatures in comparison with the lowlands.

Absolute humidity decreases with height, relative - changes little.

The least cloudiness in the mountains is observed in winter. This is explained by the fact that in winter the level of condensation is lower than in summer, and, accordingly, clouds are located lower, exposing mountain ranges. The amount of clouds is greater on the windward slopes, and less on the leeward slopes.

There is more precipitation in the mountains, but this increase occurs only up to a certain height, depending on geographical conditions, the time of year. So, in the Central Caucasus, the amount of precipitation increases to a height of 3000 m, and then begins to decrease. Precipitation falls more on the slopes facing the damp winds.

In high mountains, at a certain height, there is a snow line, above which snow lies all year round.

The height of the snow line depends on the geographic latitude, the exposure of the slopes, and the continentality of the climate. In polar countries, it is low; as you move south, the snow line rises and in tropical latitudes reaches a height of 4500-5000 m.

Mountains have a great influence on the wind: they delay air masses and change the direction of their movement. In addition, local winds are created in the mountainous area in the form of foehn, bora, mountain-valley and glacial winds.

Atmospheric fronts are also influenced by mountains. When approaching a mountain range, the front slows down its movement. If the ridge is high enough, then the front goes around it from the sides. If cold air flows over a high mountain range, then warm, dry weather sets in on the leeward side due to the adiabatic heating of the air as it descends (foehn effect). If the ridge is low, then the lowering of cold air causes the phenomenon of bora. If a warm front approaches a mountain range, it is strongly deformed and its profile is restored only at a distance of 200-300 km from the range.

Mountain ranges have a great influence not only on the climate of the area where they are located, but also on the climate of the areas adjacent to them. Detaining air masses, especially cold ones, mountain ranges can be a boundary separating regions with different climatic conditions. Thus, under the influence of the Caucasus Range, the warm climate of Transcaucasia differs from the harsh climate of Ciscaucasia. Even low elevations (for example, Central Russian, Volga, etc.) can influence the climate in flat terrain.

Mountainous regions are characterized by a large unevenness (spotting) of the spatial distribution of climatic characteristics.

Altitudinal climatic zonality takes place in the mountains. This phenomenon consists in the fact that in the mountains the change in meteorological elements with height creates a rapid change in the entire complex of climatic conditions. Formed located one above the other climatic

sky zones (or belts) with corresponding changes in vegetation. This change in altitude climatic zones resembles a change in climatic zones in the latitudinal direction, with the only difference being that for changes that occur in the horizontal direction over thousands of kilometers, in the mountains only a change in altitude is needed by kilometers. At the same time, the vegetation in the mountains is replaced in the following order: first they go deciduous forests(in dry climates they do not start from the foot, but from a certain height), then follow coniferous forests and shrubs, alpine vegetation of grasses and creeping shrubs; further, behind the snow line, there is a zone of snow and ice.

7. CLASSIFICATION OF CLIMATES

On the surface of the globe, there is big variety climates. There are various classifications that bring the climates of the globe into a certain system and give the boundaries of the distribution of certain types of climate. The latter is of great practical value, since the economic activity of man, the vital activity of animals and plant organisms is associated with climate.

LANDSCAPE-BOTANICAL CLASSIFICATION OF CLIMATES L.S. BERGA

The landscape-botanical classification of climates developed by L.S. Berg. The classification covers land. In accordance with this classification, climates are distinguished: eternal frost; tundra; taiga; deciduous forests, temperate zone; monsoon climate of temperate latitudes; steppes; Mediterranean; subtropical forests; extratropical deserts; subtropical deserts; savannah; humid tropical forest.

The climate of eternal frost is created in the Arctic (glacial plateaus of Greenland, Franz Josef Land, part of Novaya Zemlya, Severnaya Zemlya), in Antarctica. The annual radiation balance is negative. The warmest is the Atlantic-European part of the Arctic. The average January temperature in Svalbard is -13.5 °C, the average July temperature is from 2 to 10 °C. The climate of the Asian sector of the Arctic is more continental. The average temperature in January is below -30 °С, in July 2-8 °С. The most severe climatic conditions in Greenland. The thickness of the ice in the central part of the island is 3400 m. The temperature in January is 49 °С, in July -13 °С, the minimum temperatures can drop to -64 °С. The climate of Antarctica is more severe than the Arctic.

Average temperatures in July-August on the coast are from -15 to -25 °С, in inland areas -50 -5 - -70 °С and lower. In summer, on the coast -5 °С (in the depth -28 -35 °С). siege