Local winds, the reasons for their formation. winds. Local winds Strong cold gusty local wind

Afghan- dry, baking local wind, with dust that blows in Central Asia. It blows from several days to several weeks. Early spring with showers. Very aggressive. Barguzin- a mighty Baikal wind blows in the central part of the lake from the Barguzin valley across and along Baikal. This wind blows evenly, with gradually increasing power. Usually precedes a steady sunny weather. Bizet- cold and dry north or northeast wind in the mountainous regions of France and Switzerland. Bora- a strong gusty cold wind blowing on the coast of the seas or large lakes from mountain ranges separating a very chilled and more warm surface at their feet. at a speed (up to 40-60 m/s) it rolls down from the mountain ranges to the still unfrozen sea or lake. A squally wind brings a severe cooling, Bora lasts from several days to a week. Coast Adriatic Sea, near Novorossiysk (northeast wind), on the western slope of the Urals. Breeze- local wind of low speed, changing direction twice a day. Occurs on the shores of the seas, lakes, sometimes big rivers. Therefore, the daytime breeze blows from the water area to the heated coast. Night (coastal) - from the chilled coast to warm water. Mountain valley winds are formed in mountainous areas and change their direction twice a day. The air is heated differently over the crests of mountain ranges, slopes and the bottom of the valley. During the day, the wind blows up the valley and slopes, and at night, on the contrary, from the mountains to the valley and down towards the plain. Speed ​​10 m/s. Zephyr- the wind that prevails in the eastern Mediterranean since spring. Here, although warm, it often brings rain and even storms with it, while in the western Mediterranean Zephyr is almost always light. Mistral- On the Mediterranean coast of France, a cold northwest wind, which forms like a Novorossiysk bora. Simoom- a sultry dry wind in the deserts of North Africa and the Arabian Peninsula. There is a sumum with strong heating of the earth and air in cyclones and mainly with western and southwestern winds. At the same time, the air temperature can rise up to +50°C, and relative humidity approaches 0%. The squall lasts from 20 minutes to 2-3 hours, sometimes with a thunderstorm. On Lake Baikal, bora has a local name - sarma. This wind is formed when the cold arctic air passes over the coastal mountain ranges. Sirocco- hot, dry, dusty south and southeast wind from the deserts of North Africa and the Arabian Peninsula, arising in front of the cyclone. Above mediterranean sea sirocco is slightly enriched with moisture, but still dries up the landscapes of the coastal regions of France, the Apennine and Balkan Peninsulas. Most often it blows in the spring for 2-3 days in a row, raising the temperature to 35°C. Crossing the mountains, on their leeward slopes it acquires the character of a foehn. Sukhovey- wind from high temperature and low relative humidity in the steppes, semi-deserts and deserts, is formed along the edges of anticyclones and lasts for several days, increasing evaporation, drying up the soil and plants. Dry winds are typical for the steppe regions of Russia and Ukraine, for Kazakhstan and the Caspian region. Föhn- dry, warm strong wind, blowing with high mountains into the valleys. Foehn is well expressed in the Alps, in the Caucasus, in the mountains of Central Asia. Khamsin- dry, exhaustingly hot wind of the southern directions in the northeast of Africa and in the countries of the Middle East. Temperature 40°C, blows sometimes 50 days a year, usually in March-May. Occurs in the front parts of cyclones moving from the deserts of North Africa. Chinook- southwestern föhn on the eastern slopes of the Rocky Mountains in Canada and the United States, as well as on adjacent parts of the prairies. Accompanied by a very rapid, sharp increase in air temperature Chinook is also called a humid southwest wind with Pacific Ocean on the west coast of the USA. The reason for their formation may be different temperature conditions on the shores of lakes or rivers, in mountains and valleys. Some of them are essentially air currents of the general circulation of the atmosphere, but in a certain area they have special properties. emergence local winds mainly due to the difference in temperature conditions over large reservoirs (breezes) or mountains, their spread relative to the general circulation flows and the location of mountain valleys (foehn, bora, mountain-valley), as well as changes in the general circulation of the atmosphere by local conditions (samoum, sirocco, khamsin). Some of them are essentially air currents of the general circulation of the atmosphere, but in a certain area they have special properties, and therefore they are referred to as local winds and given their own names.

1. Breeze.

2. Mountain-valley winds.

3. Glacial winds.

4. Föhn.

5. Bora.

6. Flurries.

7. Atmospheric vortices of small sizes.

Local wind - wind in a certain limited area, which has characteristic features explained by the geography of this area.

He can be:

the result of the influence of (usually reinforcing) local topography or orography on currents of the general circulation of the atmosphere (foehn, bora, mistral, pass wind, canyon wind);

the manifestation of local circulation, independent of the general circulation of the atmosphere (breeze, mountain-valley wind);

manifestation of convection, sometimes vortex character ( dust storm, habub, etc.);

the course of the general circulation of the atmosphere with special properties for a given region: dryness, dustiness, low temperature at considerable speed (Afghan, sirocco, snowstorm, khamsin, simum). Winds of this category have numerous names in different regions of the Earth.

1. Breeze

Breeze(from the French brise- light wind) is a wind with a daily frequency along the shores of the seas and large lakes, as well as on some large rivers.

Breezes are formed due to the difference in temperature associated with the unequal specific heat capacity, thermal conductivity, and what about the different albedo of land and water.

They are related to the daily course of air temperature.

The daytime breeze blows from the sea (water surface) to the heated coast (Figure 78). It is also called marine. During the day, land, the specific heat of which is less than water, heats up more. The air above it also heats up more. Therefore, the isobaric surfaces above the land rise somewhat. Above the surface of the earth (at a certain height), the outflow of air begins towards the sea, and in the surface part - in the opposite direction. Because If the motion develops within a short time, then the Coriolis force cannot balance the baric gradient. The wind deviates from the geostrophic, i.e. blows not along the coastline, but crosses it. The sea breeze is stronger than the night coastal breeze, because. the difference between the temperature of the land and the water surface during the day is greater than at night.

The night breeze blows in the opposite direction to the day breeze. At night, land in coastal areas cools faster than water. At the same time, the air over land cools rapidly due to thermal conductivity and becomes denser. Isobaric surfaces over land descend. At altitudes, air transfer occurs, directed from the reservoir to the land. An area is created above the water surface reduced pressure. Then the air in the surface part begins to move from land to the reservoir.

The wind speed with breezes is 3–5 m/s, and more in the tropics. During the passage of cyclones, the breezes are masked by the general transport of air. In height, the breezes capture a layer of air up to 1–2 km (daytime more than nighttime). Deep into the sea or land, the breezes spread for tens of kilometers.

The sea breeze brings cooling and an increase in the relative humidity of the air (the temperature drops by 2–3°C (in West Africa by 10°C), humidity increases by an average of 10–20% (up to 40%).

1. Before flying and entering the air traffic services shift, analyze aerosynoptic materials, Special attention on AT-400, 300 and 200 hPa maps, atmospheric radio sounding data, maps of maximum winds (Fig. 11.9).

2. If during the flight a tail MT is observed, it is necessary to use it. In this case, it is recommended to fly in its central part and or on the right side.

4. It is possible to cross ST below the axis by 1.5…2.0 km or above the tropopause.

5. If you get into the turbulence zone associated with a passing ST, you need to change the level or deviate to the right (taking into account the temperature deviation from SA).

7. When an ST is detected, the aircraft commander is obliged to immediately inform the air traffic controller about its direction, speed and phenomena associated with it.

8. It is possible to detect ST in flight by cloud bands stretching along its direction,

and for the demolition of the aircraft, while:

If a strong left drift is observed and the air temperature a rises, then BC enters the ST from the left side;

If a strong right drift is observed and the air temperature drops, then the BC enters the ST from the right side;

If during level flight along the ST, the air temperature remains constant, and the ground speed increases (decreases), then the ST is tail (oncoming).

In some areas, under the influence of local physical and geographical conditions, air currents are formed that have a relatively small horizontal and vertical extent and differ in characteristic features. Such air currents are called local winds . They can arise due to uneven heating of the underlying surface (land, water, mountain slopes and valleys) or due to the peculiarities of air flow around orographic obstacles. Local winds include breezes, mountain-valley winds, glacial winds, bora, foehn, and others.

breezes- these are winds with daily periodicity, arising on the coasts of the seas, large lakes and wide rivers. The reason for their occurrence is uneven heating and cooling of land and sea during the day.

Daytime (sea) breeze blows from the cold water surface to the heated land, and night (coastal) breeze - from cooled land to a warmer water surface (Fig. 10.7).

The sea breeze arises at about 9...11 am local time, spreads inland for 20...40 km, its vertical power reaches several hundred meters (sometimes up to 1000 m). Maximum speeds reach 4…6 m/s and are observed in the afternoon.

The coastal breeze is formed after sunset and during the night it penetrates deep into the sea for 8–10 km.

Rice. 10.7. Scheme of formation of breeze circulation

At moderate latitudes, breezes are observed in the warm half of the year; they are more clearly expressed in clear weather if there is no or weakened overall air transport. Above the breeze, there is a wind of the opposite direction of approximately the same vertical power, called anti-breeze .

Well-developed breezes are observed in the Black, Azov and Caspian seas, weaker - in the White Sea, Ladoga and Onega lakes. In tropical areas, breezes are observed all year round.

When flying in areas where breeze circulation is observed, it is necessary to take into account the change in wind directions near the ground and at the height of the circle in the morning and evening hours.

Mountain valley winds- like breezes, they have a daily periodicity and arise due to uneven heating and cooling of the slopes of mountains and valleys day and night (Fig. 10.8).

Rice. 10.8. Scheme of the formation of mountain-valley winds

During the day, the slopes of the mountains and the air adjacent to them heat up faster and stronger than the air removed from the slopes. As a result, lighter warm air rises up the slopes of the mountains. Such a wind is called valley .

At night, the mountain slopes and the air adjacent to them cool faster than the air away from the slopes. Therefore, colder air descends along the slopes. This is how it is formed mountain wind .

The speed of long winds usually does not exceed 3...6 m/s, and the speed of mountain winds

can reach 20 m/s or more. This can lead to strong turbulence and sharp drops of aircraft down.

Glacial winds blow over the glacier downstream of the glacier. They do not have a daily periodicity, because the glacier cools the air throughout the day. Over the glacier, as a rule, there is an inversion, therefore cold air blows (flows) down. Over the glaciers of the Caucasus, the speed of such winds reaches 5...7 m/s. Glacial winds in

are observed on a large scale in Antarctica. Here they are called katabatic winds . Due to the fact that the movement of air in this case is affected not only by the force of the horizontal baric gradient, but also by the force of gravity of the Earth, the speed of katabatic winds reaches 20 m/s and more.

Bora- this is a strong cold gusty wind that occurs when cold air is dumped from low coastal mountains on the coast and a fairly warm sea. The most famous Novorossiysk bora (an average of 46 days a year) is on the northeastern coast of the Black Sea (Fig. 10.9).

Rice. 10.9. Scheme of the Novorossiysk bora in the collapse stage

It is formed in those cases when a high region is established over the Krasnodar Territory of Russia, and above the Black Sea - low pressure. The cold air mass accumulates in front of the Markhotsky pass (height 450 m) and, reaching its top in front of Novorossiysk, collapses down. The wind speed reaches 40…60 m/s and more. Cold air, mixing with warm air near the sea surface, reaches a state of saturation. If at the same time the air temperature is below 0°C, favorable conditions are created for the formation of ice.

local winds type of pine forests in different geographical areas are called: Sarma - near the Olkhov gates on Baikal; Nord - in the Baku region; Mistral - on the Mediterranean coast of France (from Montpellier to Toulon); Northser - in the Gulf of Mexico (Mexico, Texas); Oroshi - on the ocean coast of Japan.

Föhn- this is a dry, warm, gusty wind that occurs when the air flows over large mountain ranges and spreads far into the plain. It can be observed at any time of the year and day. main reason its formation is the flow of air over the top of the mountain. Relatively warm air rises along the windward slope and cools down to the condensation level by 1°C for every 100 m, above the condensation level - by an average of 0.5°C for every 100 m. The rise of air will be accompanied by the condensation of water vapor, the formation clouds and precipitation (Fig. 10.10). Having reached the top of the mountain, the air will begin to cross over it and descend along the slope on the leeward side of the mountain. When descending, the air will heat up by 1° per 100 m, as a result of which the clouds are washed away from the leeward side, and the air in the valley comes dry and warm.

Rice. 10.10. Foehn formation scheme

Changes in temperature and humidity could be very rapid and abrupt:

1…2 hours the temperature can rise by 30…40°С. The duration of the foehn varies from several hours to 5 days or more. Foehn speed ranges from calm to 15...20 m/s, foehns with a speed of 30...40 m/s were noted.

When flying in areas where there is a hair dryer, suction may occur

aircraft to the mountain, sometimes there are sharp throws down.

Foehns can occur in all mountainous areas, they are especially frequent in the Alps,

Carpathians, in the Caucasus, in the mountains of Central Asia and the Far East.

By local winds called winds that have a local distribution. They arise in connection with geographical features territory: the presence of large reservoirs, the specific orography of the region, etc.

Local winds of various origins include breezes, mountain-valley winds, slope winds, glacial winds, foehn, and bora.

breezes(fr. brise- light wind) - winds along the shores of the seas, large lakes and rivers, twice a day changing direction to the opposite: the daytime breeze blows from the reservoir to the shore, the night breeze - from the coast to the reservoir. Breezes are caused by the diurnal variation of temperature and, accordingly, pressure over land and water. They capture a layer of air 1–2 km. Their speed is low - 3 - 5 m / s. A very strong daytime sea breeze is observed on the western desert coasts of the continents in tropical latitudes, washed by cold currents and cold water rising near the coast in the upwelling zone. There, it invades inland for tens of kilometers and produces a strong climatic effect: it reduces the temperature, especially in summer, by 5–7 ° C, and in West Africa by 10 ° C, increases the relative humidity of the air up to 85%, contributes to the formation of fogs and grew up

Phenomena similar to daytime sea breezes can be observed on the outskirts of large cities, where there is a circulation of colder air from the suburbs to the center, as there are "heat spots" over the cities throughout the year.

mountain-valley winds and slope winds in the mountains they have a daily periodicity: during the day the wind blows up the valley and along the mountain slopes, at night, on the contrary, cooled heavier air descends. The daily rise in air leads to the formation cumulus clouds over the slopes of the mountains, at night the cloudiness disappears due to lowering and adiabatic heating of the air.

Glacial (katabatic) winds - these are cold winds constantly blowing from mountain glaciers down slopes and valleys. They are caused by the cooling of the air above the ice. Their speed is 5–10 m/s, but along the edges of ice sheets on the coasts of Antarctica and Greenland it can increase up to 20 m/s. The power of the stock air currents is several tens or hundreds of meters. They are more intense at night, as they are amplified by the slope winds.

Rice. 69. Scheme of the formation of a hair dryer (according to I. I. Guralnik)

hair dryer- warm, dry gusty wind blowing from the mountains to the valleys or foothills. With a hair dryer, the temperature at the foot of the leeward side of the mountains can rise by tens of degrees in a few hours, and the relative humidity can drop to 10-20%. The duration of hair dryers is from several hours to several days. The hair dryer is formed due to the fact that when ascending the windward slope of the mountains, the air cools the lower part of the path to the level of condensation along the dry adiabatic gradient (1 ° / 100 m), and the upper part of the path - along the wet adiabatic (0.5 ° / 100 m). When lowering, the air heats up dry adiabatically and comes to the foot of the mountains or to the valley with a higher temperature. The absolute and relative humidity of the hair dryer, on the contrary, is reduced. Decrease absolute humidity air is due to the formation of clouds and orographic precipitation on the windward slopes of the mountains. The relative humidity in the hair dryer also decreases as the temperature rises and, accordingly, the maximum air humidity increases. The foehn effect is more significant at higher mountain heights and in the cold half of the year, when the initial relative air humidity is higher and therefore the level of condensation on the windward side of the ridge is lower (Fig. 69).

The climatic effect of the hair dryer is significant, especially if it is intense and prolonged. Abnormally elevated air temperature is observed in places of constant development of foehns. Hairdryer can lead to descent snow avalanches, to the rapid melting of snow in the mountains and to spills mountain rivers having glacial and snow feeding. In the spring, a hair dryer can cause premature flowering of garden plants or the death of inflorescences. In summer, it either accelerates the ripening of breads and fruits, or has a detrimental effect on them. As a result of the hair dryer, summer leaf fall often occurs. Fens are frequent in the Alps (Innsbruck - 75 days a year), in the Western Caucasus and Transcaucasia (Kutaisi - 114 days), in Altai (Lake Teletskoye - 150 days), on the southern slope of the Crimean Mountains, on the northern slope of the Kopetdag (local name for fen - Garmsil), on the eastern slope of the Rocky Mountains, on the eastern lee slope of the Sierra Nevada mountains, at the foot of which there is a hot, waterless depression of Death Valley, in the Mojave Desert and in many other mountains.

Bora- a strong, cold, gusty wind blowing from the low mountains towards the relatively warm sea. Bora is fairly well studied in the region of Novorossiysk Bay on the Black Sea, where it occurs on average 46 days a year. Similar winds are observed on the Adriatic coast - in Yugoslavia and in Italy, near the city of Trieste, in the south of France (mistral), near Baku (north), on Lake Baikal (sarma) and in other places. Bora occurs in winter, from November to March, when it approaches low ridges along the coast from the land side. cold front. In the region of Novorossiysk, a strong cold wind rushes down from the mountain slope of the Varada ridge, through the Markhotsky pass, and acquires a speed of more than 20 m/s, causing destruction on land. On the surface of the water storm wind produces great excitement. At the same time, the air temperature drops sharply, often to sub-zero values. Water, falling on ships and coastal buildings, quickly freezes, covering them with an ice crust. A preventive measure to combat bora is the release of vessels into the open sea several tens of kilometers from the coast, where the wind subsides.

Depending on local conditions in some areas the globe special winds are formed. Like the constant winds, they are integral part general circulation of the atmosphere and determine the climate and weather in a given area. Local winds include a breeze that changes its direction twice a day, mountain-valley winds, bora, foehn, dry winds, simum and many others. The reason for their formation may be different temperature conditions on the shores of lakes or rivers, in mountains and valleys. Some of them are essentially air currents of the general circulation of the atmosphere, but in a certain area they have special properties, and therefore they are referred to as local winds and given their own names.

Mountain-valley winds are formed in mountainous regions and change their direction twice a day. The air is heated differently over the crests of mountain ranges, slopes and the bottom of the valley. During the day, the wind blows up the valley and slopes, and at night, on the contrary, from the mountains to the valley and down towards the plain. The speed of mountain-valley winds is low - about 10 m/s.

Bora (Italian bora from Greek boreas) is a strong gusty cold wind blowing from the mountains on the coast of the seas or large lakes. It is formed when low mountain ranges separate cold air over land from warm air above the water. This wind is most dangerous in frosty weather, when at high speed (up to 40-60 m/s) it rolls down from the mountain ranges to the still unfrozen sea or lake. Over a warm water surface, the temperature contrast between the flow of cold air and warm sea increases significantly, and the speed of the bora increases. A squally wind brings a severe cold snap, raises high waves, and splashes of water freeze on the hulls of ships. Sometimes a layer of ice up to 4 meters thick grows on the windward side of the ship, under the weight of which the ship can capsize and sink. Bora lasts from several days to a week.

On Lake Baikal, bora has a local name - sarma. This wind is formed when the cold arctic air passes over the coastal mountain ranges. It is named after the Sarma River, through the valley of which the cold wind from Yakutia breaks through to Baikal. In 1912, this icy wind tore a huge barge from the tugboat and threw it onto a rocky shore. More than 200 people died as a result.

On the Mediterranean coast of France, a cold northwest wind, which forms like the Novorossiysk bora, is called the mistral, and a similar wind on the coast of the Caspian Sea in the Baku region is called the nord.

Pampero is a cold southerly or southwesterly storm wind in Argentina and Uruguay associated with intrusions of Antarctic air.

Föhn is a warm strong wind blowing from high mountains to valleys. It is often formed in the Caucasus and in the mountains of Central Asia. Dry air rushes into the valley, and as it descends, its temperature rises as a result of adiabatic heating - by one degree for every 100 m of descent. The higher the height from which the hair dryer descends, the higher the temperature of the air brought by it rises. The speed of the hair dryer can reach 20-25 m/s. In winter and spring, it causes rapid snowmelt, an increase in the level of mountain rivers. In summer, its withering breath is detrimental to plants; sometimes in the Transcaucasus, a summer hair dryer causes the leaves on the trees to dry out and fall off.

Dry winds often blow in the steppes, deserts and semi-deserts in summer. These hot dry winds form along the edges of anticyclones and last for several days, increasing evaporation, drying up the soil and plants. Dry winds are typical for the steppe regions of Russia and Ukraine, for Kazakhstan and the Caspian region.

Samum - a sultry wind in the deserts of North Africa and the Arabian Peninsula - is formed when the air is strongly heated in cyclones. It carries hot sand and dust and is sometimes accompanied by a thunderstorm. The air temperature can rise up to +50°C. Usually, before the oncoming squall of the simum, the sands begin to “sing” - the sound of grains of sand rubbing against each other is heard.