SECTION 3 GEOGRAPHIC SHELL

Topic 2. Atmosphere

§ 36. Wind. Constant and variable winds

Remember

How do you watch the wind?

What winds prevail in your area?

Wind is the movement of air in a horizontal or close direction. In this case, air moves from an area of \u200b\u200bhigh atmospheric pressure to an area of \u200b\u200blow atmospheric pressure. The wind is characterized by speed, strength and direction. Wind speed is measured in meters per second (m / s) or kilometers per hour (km / h). To convert meters per second to kilometers per hour, you need to multiply the speed value in meters per second by 3.6.

Wind force is determined by the pressure of the moving air on objects. It is measured in kilograms per square meter (kg / m2). The strength of the wind depends on its speed. Thus, the wind at a speed of 100 km / h has a force 10 times greater than that at a speed of 10 km / h. The greater the difference in atmospheric pressure values, the stronger and faster the wind blows. The absence of any signs of wind is called calm.

Modern facts

Strongest winds. The "pole of the winds" on Earth is considered the outskirts of Antarctica, where winds blow for 340 days a year. The highest wind speed - 371 km / h - was registered in 1934 in the USA, on a mountain in the state of New Hampshire. In Ukraine, the strongest was the wind on Ai-Petri in the Crimea (its speed reached 180 km / h).

The direction of the wind is determined by the position of the side of the horizon from which it blows. In practice, the horizon is divided into eight directions to indicate the direction of the wind. Of these, four head ones - north (Mon), south (S), east (Cx) and west (W) and four intermediate ones - northeast (North-East), north-west (North-West), southeast ( Pd-Cx) and southwestern (Pd-Zx).

For example, when the wind blows from an area located between south and east, it is called southeast (Pd-Cx). The direction and speed of the wind is determined using a weather vane (Fig. 97). A visual representation of the directions of the winds that prevail in a given area is given by a special diagram - wind rose (Fig. 98). This is a graphical representation of the repeatability of wind directions. The length of its rays is proportional to the frequency of the winds in a given direction.

Fig. 97. Weather Vane

PRACTICAL WORK No. 8(continued)

Observing the weather: composing a wind rose

Using the data in the table, build a wind rose. To do this, first draw the coordinates, indicating four wind directions and four in between. At your chosen scale, set aside the number of lines corresponding to each direction. Connect the ends of the segments in series with each other. Paint over the resulting wind rose and indicate which direction of the wind prevailed. In figure 98, notice how the winds of different directions are indicated.

Fig. 98. Wind Rose

Constant and variable winds. There is not a single windless place on the globe. There are many different types of winds. There are winds that blow constantly, and there are those that change their direction during the day or year. Constant winds - trade winds - occur between the high tropical and equatorial low belts of atmospheric pressure in the Northern and Southern hemispheres of the Earth (Fig. 99). Due to the rotation of the globe, trade winds in the Northern Hemisphere move from northeast to southwest, and in the South - from southeast to northwest. The trade winds hardly change their direction throughout the year. their speed is on average 5-6 m / s, and the vertical thickness reaches 2-4 km and increases towards the equator.

In temperate latitudes, westerly winds blow. They are also permanent.

Fig. 99. Formation of trade winds

Fig. 100. Formation of day (a) and night (b) breezes

There are much more variable winds on the globe than constant ones. Distributed only in certain areas, they are called local.

Local winds blow over a relatively small area (from hundreds of meters to tens of kilometers) and significantly affect the weather in the area. An example of a local wind is a breeze. Translated from French, this word means "light breeze." Its speed is really insignificant - up to 4 m / s. The breeze blows at daily intervals on the coast of the seas, large lakes and some large rivers... This wind changes its direction twice a day, which is caused by uneven heating of the land surface and the reservoir. The daytime, or sea, breeze moves from the water surface to the land, and the night, or coastal, - from the cooled land coast to the reservoir (Fig. 100).

The breeze occurs mainly in summer, when the temperature difference between land and water reaches the greatest values. In Ukraine, breezes are observed on the coast of reservoirs, the Black and Azov seas.

Amazing phenomena

Wind from mountain peaks.

Interesting local winds are fioni, which do not have a specific periodicity. They are not permanent and last on average from one to two days.

Fyon is a strong, gusty, dry and warm wind blowing from mountain peaks to valleys. It occurs when the air passes over the crest of a mountain ridge and, dropping down the slope, quickly heats up (Fig. 101). In this case, the temperature can reach maximum values for a given time of year. So, with a strong fioni on the icy island of Greenland, the temperature rises by 20-25 ° C. Fyon causes snow to melt in the mountains in winter and droughts and fires in summer. In the mountainous regions of Ukraine, fioni that blow from the southeastern slopes of the Crimean mountains near Alushta can suddenly increase the temperature here to 28 ° C. Fioni in the Ukrainian Carpathians have a speed of up to 25 m / s.

Fig. 101. Formation of fions

Fig. 102. Moving Monsoons

Monsoons are also referred to as winds changing their direction. The word "monsoon" is translated from Arabic as "season". This name is not accidental, because the monsoon changes its direction twice a year: in winter it blows from land to ocean, and in summer, on the contrary, from ocean to land (Fig. 102). (Consider why the monsoon changes direction with the seasons.) Monsoon winds are most pronounced in the south and east of Asia, in the north of the Indian and in the west The Pacific... The Asian summer monsoon is especially powerful. It contains a large number of moisture and heat, heavy precipitation is associated with it.

Wind is the horizontal movement of air, resulting from the difference in atmospheric pressure.

The wind is characterized by speed, strength and direction.

Constant winds blow constantly, variable winds change their direction during the day or year.

Questions and tasks for self-examination

Build a wind rose from your observations. Explain which winds prevail in your area. Sketch the wind direction according to the following data: a) the pressure at point A is 760 mm Hg. Art., and in point B - 784 mm Hg. Art .; b) the pressure on the coast is 758 mm Hg. Art., and over the lake - 752 mm Hg. Art. When will the wind be stronger?

Choose from the listed winds the one that hardly changes its direction: a) trade wind; b) monsoon c) breeze.

What is the cause of the wind? What determines the strength and speed of the wind?

Wind formation

Although the air is invisible to the eye, we always feel its movement - the wind. The main cause of wind is the difference in atmospheric pressure over areas of the earth's surface. As soon as the pressure somewhere decreases or increases, the air will be directed from the place of higher pressure towards the lower one. And the balance of pressure is disturbed by unequal heating of different parts of the earth's surface, from which the air is heated in different ways.

Let's try to imagine how this happens using the example of the wind that occurs on the coast of the seas and is called breeze... Areas of the earth's surface - land and water - are heated differently. The dry land heats up faster. Therefore, the air above it will heat up faster. It rises up, the pressure decreases. At this time, the air above the sea is colder and, accordingly, the pressure is higher. Therefore, the air from the sea moves to land to a warm place. So the wind blew - day breeze... At night, everything happens the other way around: land cools faster than water. Above it, the cold air creates more pressure. And above water, it retains heat for a long time and cools slowly, the pressure will be lower. Cold air from land from the high pressure area moves towards the sea, where the pressure is lower. Arises night breeze.

Therefore, the difference in atmospheric pressure acts as a force, causing the horizontal movement of air from the high pressure area to the low pressure area. This is how the wind is born.

Determination of wind direction and speed

The direction of the wind is determined beyond the side of the horizon from which it blows. If, for example, the wind blows from the event, it is called western. This means that the air moves from west to east.

Wind speed depends on atmospheric pressure: the greater the difference in pressure between areas of the earth's surface, the stronger the wind. It is measured in meters per second. Near the earth's surface, winds often blow at a speed of 4-8 m / s. In ancient times, when there were no instruments yet, the speed and strength of the wind was determined by local criteria: at sea - by the effect of the wind on the water and the sails of ships, on land - along the tops of trees, the deflection of smoke from chimneys. On many grounds, a 12-point scale was developed. It allows you to determine the strength of the wind in points, and then its speed. If there is no wind, its strength and speed are equal to zero, then this is calm... The wind with a force of 1 point, barely swaying the leaves of the trees, is called quiet... Further on the scale: 4 points - moderate wind (5 m / s), 6 points - strong wind (10 m / s), 9 points - storm (18 m / s), 12 points - hurricane (Over 29 m / s). At meteorological stations, the strength and direction of the wind is determined using weather vane, and the speed is anemometer.

The strongest winds near the earth's surface blow in Antarctica: 87 m / s (individual gusts reached 90 m / s). The highest wind speed in Ukraine was recorded in Crimea at sorrow - 50 m / s.

Monsoon is a periodic wind carrying a large amount of moisture, blowing from land to ocean in winter, and from ocean to land in summer. Monsoons are observed mainly in tropical belt... Monsoons are seasonal winds that last several months of each year in tropical areas. This term originated in British India and surrounding countries as a name for seasonal winds that blow from the Indian Ocean and Arabian Sea to the northeast, bringing significant rainfall to the region. Their movement towards the poles is caused by the formation of low pressure areas as a result of the heating of tropical regions in the summer months, that is, Asia, Africa and North America from May to July and in Australia in December.

Trade winds are constant winds blowing with a fairly constant force of three to four points; their direction practically does not change, only slightly deviating. The trade winds are called the near-surface part of the Hadley cell - the predominant near-surface winds that blow in the tropical regions of the Earth in a westerly direction, approaching the equator, that is northeasterly winds in the Northern Hemisphere, and the southeastern in the Southern. The constant movement of trade winds leads to mixing of the Earth's air masses, which can manifest itself on a large scale: for example, the trade winds blowing over the Atlantic Ocean are capable of transporting dust from the African deserts to the West Indies and parts of North America.

Local winds:

Breeze is a warm wind blowing from shore to sea at night and from sea to shore during the day; in the first case it is called a coastal breeze, and in the second it is called a sea breeze. Marine and continental breezes are important effects of the formation of predominant winds in coastal areas. The sea (or a smaller body of water) heats up more slowly than land due to the greater heat capacity of water. Warmer (and therefore lighter) air rises above land, creating zones of reduced pressure. The result is a pressure drop between land and sea, which is usually 0.002 atm. This pressure drop causes the cool air above the sea to move towards land, creating a cool sea breeze on the coast. Due to the absence of stronger winds, the speed of the sea breeze is proportional to the temperature difference. If there is wind from the land side with a speed of more than 4 m / s, the sea breeze usually does not form.

At night, due to its lower heat capacity, the land cools faster than the sea, and the sea breeze stops. When the land temperature drops below the surface temperature of the reservoir, a reverse pressure drop occurs, causing (in the absence of strong wind from the sea) continental breeze that blows from land to sea.

Bora is a cold, sharp wind blowing from the mountains to the coast or valley.

Foeong is a strong warm and dry wind blowing from the mountains to the coast or valley.

Sirocco is the Italian name for a strong southerly or southwesterly wind that originates in the Sahara.

Variable and constant winds

Variable winds change their direction. These are the splashes already known to you (from the French "Breeze" - light wind). They change their direction twice a day (day and night). Splashes occur not only on the coasts of the seas, but also on the shores of large lakes and rivers. However, they cover only a narrow strip of the coast, penetrating into the depths of land or sea for several kilometers.

Monsoons are formed in the same way as breezes. But they change their direction twice a year for seasons (summer and winter). Translated from Arabic "monsoon" means "Season". In the summer, when the air above the ocean heats up slowly and the pressure above it is greater, the moist sea air penetrates onto the land. It is the summer monsoon that carries daily thunderstorms. And in winter, when high air pressure builds up over land, the winter monsoon begins to operate. It blows from land towards the ocean and brings cold, dry weather. So, the reason for the formation of monsoons is not daily, but seasonal fluctuations in air temperature and atmospheric pressure over the continent and the ocean. Monsoons penetrate land and ocean for hundreds and thousands of kilometers. They are especially common on the southeastern coast of Eurasia.

Unlike variables, constant winds blow in one direction throughout the year. Their formations are associated with high and low pressure belts on Earth.

Trade winds - Winds that blow throughout the year from high pressure belts near the 30th tropical latitudes of each hemisphere to the low pressure belt at the equator. Under the influence of the Earth's rotation around the axis, they are not directed directly to the equator, but deviate and blow from the northeast in the Northern Hemisphere and from the southeast in the South. The trade winds, characterized by uniform speed and surprising consistency, were the favorite winds of sailors.

From tropical high-pressure belts, winds blow not only to the equator, but also in the opposite direction - to latitudes 60 with low pressure. Under the influence of the deflecting force of the Earth's rotation with distance from tropical latitudes, they gradually deviate to the east. This is how air moves from west to east and these winds in temperate latitudes become western.

Windiness in the modern dictionary is synonymous with inconstancy, changeability. But the trade winds completely break this statement. Unlike breezes, seasonal monsoons and even more winds caused by weather cyclones, they are constant. How are trade winds formed and why do they blow in a strictly defined direction? Where did this word "trade wind" come from in our language? Are these winds really so constant and where are they localized? You will learn about this and much more in this article.

The meaning of the word "trade winds"

In the days of the sailing fleet, the wind was of paramount importance for navigation. When he always blew exactly in the same direction, one could hope for a successful outcome of the dangerous journey. And such a wind was dubbed by the Spanish sailors "viento de pasade" - favorable for movement. The Germans and Dutch included the word "pasade" in their nautical vocabulary of nautical terms (Passat and passaat). And in the era of Peter the Great, this name penetrated into the Russian language. Although trade winds are rare in our high latitudes. Their main "habitat" is between the two tropics (Cancer and Capricorn). Trade winds are observed and further from them - up to the thirtieth degree. At a considerable distance from the equator, these winds lose their strength and are observed only in large open spaces, over the oceans. There they blow with a force of 3-4 points. Off the coast, trade winds transform into monsoons. And even farther from the equator, they give way to winds generated by cyclonic activity.

How trade winds are formed

Let's do a little experiment. Apply a few drops to the ball. Now let's spin it like a whirligig. Take a closer look at the drops. Those of them, which are closer to the axis of rotation, remained motionless, and the whirligig located on the sides spread in the opposite direction. Now let's imagine that the ball is our planet. It spins from west to east. Opposite winds are formed from this movement. When a point is located close to the poles, it makes a smaller circle per day than that located at the equator. Therefore, the speed of its movement around the axis is slower. Air currents do not arise from friction with the atmosphere in such polar latitudes. It is now clear that the trade winds are the steady winds of the tropics. At the very equator, there is a so-called calm band.

Direction of trade winds

Drop by drop on the ball is easy to see that they spread in the opposite direction of rotation. This is called But to say that the trade winds are winds blowing from east to west would be wrong. In practice, the air masses deviate from their main vector to the south. The same thing happens, only in a mirror image, on the other side of the equator. That is, in the Southern Hemisphere, trade winds blow from the southeast to the northwest.

Why is the equator so attractive for air masses? In the tropics, as is known, a constant high pressure region is established. And the equator, on the contrary, is low. If we answer a child's question, where does the wind come from, then we will present a common natural history truth. Wind is the movement of air masses from high-pressure layers to lower-pressure layers. In science, the periphery of the tropics is called “Equine latitudes”. From there, the trade winds blow at a gallop into the "Calm strip" above the equator.

Constant wind speed

So, we understood the distribution area of \u200b\u200bthe trade winds. They are formed in both at a latitude of 25-30 ° and fade out near the calm zone somewhere around 6 degrees. The French consider the trade winds to be “vents alizes”, very comfortable to sail. Their speed is small, but constant (five to six meters per second, sometimes it reaches 15 m / s). However, the power of these air masses is so great that they form trade wind currents. Born in hot regions, these winds contribute to the development of deserts such as the Kalahari, Namib and Atacama.

Are they so permanent?

Over the continents, trade winds collide with local winds, sometimes changing their speed and direction. For example, in the Indian Ocean, due to the special configuration of the coast South-East Asia and climatic characteristics, the trade winds turn into seasonal monsoons. As you know, they blow from the cool sea towards the heated land in summer, and vice versa in winter. However, the statement that the trade winds are tropical winds is not entirely true. In the Atlantic, for example, in the Northern Hemisphere, they blow in winter and spring within 5-27 ° N, and in summer and autumn 10-30 ° N. Back in the 18th century, he gave this strange phenomenon scientific explanation John Hadley, British astronomer. The strip of calm does not stand at the equator, but moves after the Sun. Thus, by the date when our star stands at its zenith over the Tropic of Cancer, the trade winds are shifting to the north, and in winter to the south. Constant winds are not the same in strength. The Southern Hemisphere trade winds are more powerful. He almost never encounters obstacles in the form of land. There it forms the so-called "roaring" forties.

Trade winds and tropical cyclones

To understand the mechanics of typhoon formation, you need to understand that two constant winds blow in each hemisphere of the Earth. Everything that we have described above refers to the so-called lower trade winds. But the air, as you know, cools when climbing to a height (on average, one degree every hundred meters ascending). Warm masses are lighter and rush upward. Cold air tends to sink. Thus, opposite trade winds arise in the upper atmosphere. blowing in the Northern Hemisphere from the southwest, and below the equator - from the northwest. inside the trade winds it sometimes changes the stable direction of two layers. A zigzag swirling of warm, moisture-saturated and cold air masses occurs. In some cases, tropical cyclones gain the strength of a hurricane. All the same directional vector inherent in the trade winds carries them to the west, where they unleash their destructive force on the coastal areas.

The air masses surrounding us are in continuous motion: up and down, horizontally. We call the horizontal movement of air the wind. Wind flows are formed according to their own specific laws. To characterize them, indicators such as speed, strength and direction are used.

The winds of different climatic regions have their own features and characteristics. The temperate latitudes of the Northern and Southern Hemispheres are blown by westerly winds.

Constants and variables

Wind direction is determined by high and low pressure areas. Air masses move from high pressure to low pressure areas. The direction of the wind also depends on the action of the earth's rotation: in the northern hemisphere, the currents are adjusted to the right, in the southern - to the left. Air flows can be both constant and variable.

Westerly winds of temperate latitudes, trade winds, northeast and southeast belong to the group of permanent ones. If the trade winds are called the winds of the tropics (30 o N - 30 o S), then westerly winds prevail in temperate latitudes from 30 o to 60 o in both hemispheres. In the Northern Hemisphere, these air currents deviate to the right.

In addition to constant ones, there are variable or seasonal winds - breezes and monsoons, as well as local ones, characteristic only for a particular region.

Current of the West Winds

Air, moving in a certain direction, has the ability to carry huge masses of water in the ocean, creating strong currents - rivers among the oceans. Currents generated by winds are called wind currents. In temperate latitudes, westerly winds and the rotation of the earth direct surface currents to the western shores of the continents. In the northern hemisphere, they move clockwise, in the southern hemisphere - counterclockwise. In the Southern Hemisphere, wind and earth rotation have created a strong current of the Westerly Winds along the coast of Antarctica. This is the most powerful oceanic current that encircles the entire earth from west to east in the region between 40 o and 50 o south latitude. This current serves as a barrier separating the southern waters of the Atlantic, Indian and Pacific oceans from the cold waters of the Antarctic.

Wind and climate

Westerly winds affect the climate of a large territory of the continent of Eurasia, especially on that part of it, which is located in the temperate zone. With the breath of Vesta, coolness in the heat of summer and thaw in winter comes to the continent. It is the winds from the west in collaboration with the warm ocean current that explains the fact that the climate of northwest Europe is much warmer than the same latitudes of North America. As we move inland to the east, the influence of the Atlantic decreases, but the climate becomes completely continental only beyond the Ural ridge.

In the Southern Hemisphere, violent winds from the west are not hindered by any obstacles in the form of continents and mountains, they are free and free: they storm, fight ships, rush eastward at great speed.

Who is friends with the wind

Indomitable Vesta are especially familiar to sailors on the Cape of Good Hope routes - New Zealand - Cape Horn. Having picked up a passing sailboat, they can accelerate it faster than a diesel boat. Sailors call the westerly winds gallant in the Northern Hemisphere and the roaring forties in the Southern.

The western winds also caused a lot of trouble for the first aviators. They were allowed to fly from America to Europe, as they were passing. The pilots passed the route without any problems. The situation with the flight from Europe to America was completely different. Of course, the wind is not a hindrance to modern supersonic liners, but in the 1920s and 1930s, it turned out to be a significant obstacle.

So the French pilots Ningesieres and Collie in 1919 made a historic flight across the Atlantic Ocean on the route Newfoundland - Azores - Iceland. But the same way in the opposite direction ended tragically. The pilots intended to repeat the famous route of Columbus by air, only 34 years later the wreckage of their plane was discovered on the US coast.

The tragedy is explained by the fact that strong winds significantly delayed the aircraft, and there was simply not enough fuel to reach its destination.

Counter Vesta were the first to win soviet pilots Gordienko and Kokkinaki in 1939, having successfully overcome the French route.

Wind is a horizontal and evenly moving stream of air relative to the earth's surface. There is a huge variety of local winds, which cannot be explained using the example of ordinary observations due to their inherent specific features characteristic of a particular region. So, talking about what winds there are on the coast, for example, allow such observations: at noon a breeze blows from the sea - cool, gentle, and at night the same wind moves from land towards the sea. In deserts and mountainous areas, mainly mountain or valley winds "live". However, there are types of winds that apply to the entire planet as a whole.

What are the winds

1. Monsoon is a periodic wind that carries a lot of moisture. In winter, the monsoon blows from land to the ocean, and in summer, from the ocean to land. Monsoons are mainly dominant in the tropical belt and are inherently seasonal winds lasting several months each year.
2. The trade winds are winds with a constant character, moving with a fairly stable force of three to four points. Trade winds move in almost the same direction, sometimes deviating slightly. Such dynamics of movement leads to a mixing of the planet's air masses, up to a global scale: for example, trade winds blowing over the Atlantic Ocean can transfer dust particles from African deserts to the West Indies and several North American regions.
3. Local winds:
   • Breeze is a warm breeze blowing from the coast to the sea at night (coastal breeze) and in the opposite direction during the day (sea breeze). The main generators of prevailing winds in the coastal areas are sea and continental breezes. Due to the fact that the sea (body of water) warms up more slowly than land due to the greater heat capacity of water, the more heated air above the land rises up, forming a zone of reduced pressure. This creates a difference in atmospheric pressure between the air streams and creates a cool sea breeze on the coast.

     At night, due to its lower heat capacity, the land cools faster and the sea breeze stops. At the moment when the land temperature is lower than the temperature on the surface of the reservoir, a reverse pressure drop forms, creating (if there is no strong wind from the sea) a continental breeze moving from land to the sea.

   • Bora is a cold, harsh wind moving from the mountains to the coast or valley.
   • Fyong is a dry, strong and warm wind that moves from the mountains to the valley or coast.
   • Sirocco is the name in Italian for the southwest or strong southerly wind that forms in the Sahara Desert.
4. Variable and constant winds.

   The nature of the movement of air masses also helps to understand what winds are. So, variable winds are able to change their direction. These include the breezes already discussed above (translated from French "Breeze" means light wind), since they change the direction of their movement twice a day (day and night).

   Monsoons are born just like breezes. They change their direction of movement twice a year seasonally (summer and winter). The Arabic name for the wind is "monsoon" in translation and means "season". When the summer monsoon forms, there are thunderstorms due to strong air saturation. sea \u200b\u200bwater, and in winter dry and cold air moves from land.

5. Also, the winds can be characterized as gusty and light, or give them a name based on the direction of their movement, for example: east, south-west, etc.