What is Wind? [NCERT Geography Notes for UPSC, SSC, Railway Exams]
Posted on 19-03-2022
- As the temperature increases, air expands and its density decreases, and as the temperature decreases, air contracts, and its density increases.
- The rise in temperature produces low air pressure and the drop in temperature produces high pressure. If a region is hotter than its neighboring region, then due to the removal or rise of hot air, the air pressure there will be relatively less.
- As a result, the wind which blows from the neighboring region takes the place of the displaced or raised air, then it is called wind. The air moving in the horizontal direction is given the name 'wind'.
- The air moving in the vertical direction is called the wind current. Winds always move from high-pressure areas to a low-pressure area. The direction of low pressure is called the barometric slope. Wind speed and direction are estimated by this gradient.
Origin of wind
- Inequality of air pressure is the most important factor in the origin of wind. Uneven heating of the atmosphere is a major contributor to the inequality of air pressure. Uneven heating of the atmosphere is associated with solar radiation and terrestrial radiation.
- Hence, the motivating force for the origin of wind comes from the Sun and the Earth. The generation and direction-control of wind near the Earth's surface is the combined effect of the following factors.
- Due to the gradient of air pressure, the air is generally forced to move from a high-pressure area to low pressure area. The greater the slope, the greater the wind speed.
- The effect of rotation of the earth affects the direction of the wind along with generating the wind.
- The French physicist Coriolis (Gaspard de Coriolis, 1835) highlighted this and said that the wind deflects to its right in the northern hemisphere and to the left in the southern hemisphere.
- This deflection was proved by the American meteorologist William Ferrel, in 1856, hence, it is called 'Ferrel's law'.
- According to Ferrell's law, the divergence of wind in the northern hemisphere is clockwise, that is, clockwise. It is also called the deflection of wind.
- Winds move from high-pressure areas to low-pressure areas instead of moving vertically and deflected. Due to the slow turning speed towards the poles and fast turning towards the equator, any moving object is forced to turn and move.
- According to the law of Dutch meteorologist Baij Ballot (1857), if the wind blows from the back in the northern hemisphere, then high pressure will be on the right and low pressure on the left.
- The situation will be the opposite in the southern hemisphere. With the help of this law, the approximate direction of high pressure can be found immediately.
- Centripetal acceleration pulls the air on the rotating earth towards its center by the centripetal force. Due to this acceleration, the air makes a curve.
- Apart from the pressure gradient and the Coriolis force, it is the third force that is pulling air inward.
- The force of friction acts up to a height of 500-1000 meters above the ground where the air cannot move freely on the horizontal plane due to surface inequalities. Friction is created due to obstruction and the speed of air slows down.
- Due to the relatively less friction produced on the ocean water, the wind speed is accelerated. It is clear that the above factors affect their direction and speed, not the origin of wind. The wind is generated due to differences in air pressure.
Type of wind
- None of these conditions are met. The Earth is rotating and there is an uneven distribution of water and land on it. Therefore, different parts of it receive different amounts of insolation.
- These are the basic elements of horizontal movement of air and as far as permanent wind system is concerned, the last element is very important.
- Due to the latitudinal difference of air pressure over the entire globe, the winds which are prevalent, that is, they move permanently throughout the year, are called global winds, prevailing winds, or permanent winds.
- According to the season, the winds which change their direction are called periodical winds.
- The winds that develop due to the difference in daily temperature and air pressure are called local winds. They are given different names in different places.
Standing Wind / Global Wind
- Permanent wind refers to those winds whose direction is dependent on the arrangement of the pressure belt and which blow together throughout the year.
- The air pressure belts on the earth are almost permanent, so the wind moves from high pressure to low-pressure belts permanently.
- Due to getting maximum insolation here, the air gets heated and expands. The flow of air is vertical and the gradient of the barometer is negligible.
- Hence it is called the 'calm or doldrums' of the wind. However, this box does not remain silent everywhere.
- Its area comes under the influence of monsoon or commercial wind with the change of position at many places.
- Winds blowing permanently from high-pressure belts located near 30° latitudes to 10°-15° latitudes are called commercial winds (NE in the northern hemisphere and SW trade winds in the southern hemisphere).
- Once upon a time, these winds were a great help in commerce (by sea transport).
- These winds blow from the higher latitudes, so they remain somewhat cold but become hot and humid as they approach the equator. Their speed was not very fast.
The wind near the calm belts of ion lines
- When the air near the equator gets warm and rises, it cools there and becomes heavy and descends near 30° latitude. Here high pressure is created due to the air coming down from above.
- Surface winds remain calm (like a belt of equatorial calm winds, but the reason is different).
- The weather remains dry and cloudless. After entering this calm and uncertain windy part, traders in ancient times threw some horses from their ships into the ocean, so that there would be no difficulty in moving forward. For this reason, it got the name Horse Latitude.
Westerly or westerly wind or counter-trade wind
- Winds moving from the high-pressure belts of the ion lines (Cancer and Capricorn) to the poles (between 35°-40° latitudes to 60°-65° latitudes) are called westerly winds (or westerly winds). Their direction is south-west in the northern hemisphere and north-west in the southern hemisphere.
- Since they have an opposite direction to the trade wind, they are also called anti-trade winds. Unlike other permanent winds, these winds move from warm latitudes to colder latitudes. In these, the western-coastal regions receive rainfall throughout the year.
- Due to the movement of cyclone and anti-cyclone (anticyclone), there is a difference in their speed. They move faster in the Southern Hemisphere than in the Northern Hemisphere.
- They appear to be thundering near 40° south latitude (there is a lack of land and expansion of water, so movement is not hindered).
- Therefore, at these latitudes, they are called 'Roaring Fourties, 'Prachanda or Fierce Sixties'.
- Cold winds from the high-pressure area of the poles move around and reach the subpolar low-pressure belts. They are dry.
- Their direction is north-east in the northern hemisphere and south-east in the southern hemisphere.
- Where they meet the western winds, a cyclonic environment is present and the weather changes.
- Polar winds play an important role in generating temperate cyclones.
- Due to some special reasons, there is a disturbance in the order of permanent wind and special types of winds start blowing in a particular season.
- Such seasonal or seasonal winds have been named 'temporal winds'. Monsoon is such a wind that blows from one direction in winter and from another direction in summer. This was first told by the Arab geographer 'Alamsudi'.
- Terrestrial breeze and sea breeze (which move towards the sea during the day and land side at night) and also mountain breeze and valley breeze (which move from valley to mountain during the day and from mountain to the valley at night) i) is kept under the occasional wind.
- Monsoon originates near the Tropics of Cancer and Capricorn (in the region of trade wind).
- Its most famous region is South-East Asia, where there is a vast landmass on one side and an extensive water body (ocean) on the other.
- During the summer (June-July) the land area becomes hotter and becomes a low-pressure area. At this time, high pressure of air is found on its adjacent water body.
- As a result, the wind moves from the high-pressure area of the sea to the low-pressure area of the land and it takes the form of wind.
- Due to the high gradient of the barometer, its speed is very fast.
- Due to its movement from the sea, it also has enough moisture to make it rain.
- In winter, the landmass cools down and a high pressure area of air is formed there. Low pressure is found on the water body adjacent to it.
- So the wind starts moving towards the water in the land. Due to coming from the land, there is no moisture in the wind, but there is dryness.
- Frelon's theory is considered important in relation to the origin of the monsoon. According to him, it is a modification of the common prevailing wind system.
- It is superimposed on him and is not just a convective current. It is basically a northern extension of the south-westerly wind and equatorial low pressure.
- Frelon says that it is actually the west wind. Due to the northward shift of tropical high pressure in summer, the equatorial westerly winds embedded in the eastern winds also get influenced by it and move northwards.
- Thus, moving beyond the oceans, they start moving on the continents and the SW. Summer takes the form of a monsoon.
- In winter, the high-pressure belts of the ion lines and the thermal equator shift to the south, and the normal trade wind resumes. This is the winter monsoon.
- The areas under the influence of monsoon are- India, Bangladesh, Sri Lanka, Myanmar (Burma), S.E. Asia's Thailand, Vietnam, Kampunia, Philippines, China, Japan, Arabian Sea, S.E.C. North America and Northern Australia.
- Outside India, in the eastern countries of Asia (such as China, Japan), the winter monsoon is more stable and stronger than the summer monsoon. There the cold continental dry air mass and the warm oceanic wet air mass mix with each other to give rise to cyclones, which cause heavy rainfall.
- In East Asia, the winter monsoon winds coming from the polar region are extremely cold and cause snowfall, but this does not happen in South Asia, because the Himalayan mountain becomes a barrier in the middle.
Terrestrial and sea breeze
- These also arise as a result of uneven heating and cooling of land and water, but their effect is in the coastal parts (limited area), so some people keep them under local winds.
- During the day the landmass of the coast heats up faster than the water and conversely, it cools down very quickly after sunset.
- Thus, due to the warming of the land during the day, an area of low air pressure is formed and there is a cool slow breeze from the sea (which remains relatively cold, due to which the high-pressure area remains) which is called sea breeze.
- It does not run only after sunrise, but after some time (from about 9-10 am). Maximum 32 km towards sea breeze land. enters inside. Its effect is not seen at altitudes above 60 meters.
- At night, the land area of the beach discharges its heat more rapidly than the water, due to which high pressure is established there.
- Due to the heat in the sea, low pressure is found. As a result, a cool gentle breeze starts moving from land to sea, which is called terrestrial breeze.
- Sea and terrestrial breezes are experienced only when the sky is clear and there is no obstruction in the eclipse of insolation and dissipation of heat from the earth.
Mountain and valley breeze
- They are not related to the large center of air pressure. In the mountainous areas, during the day, the mountain tops and mountain slopes become hotter than the adjacent valley and generate low pressure, due to which the air of the valley rises there. This is called 'Valley-Sameer' or 'Ascending Wind'.
- On the contrary, due to the terrestrial radiation at night, the mountain tops cool down and due to the high pressure generated, the air from there moves towards the valley, which is called 'mountain breeze' or 'descending wind'.
- These breezes can arise in any mountainous region like the Himalayas, Alps, etc., but their development mainly takes place in the mountainous parts of the tropical region. Where cyclones do not occur.
- The mountain ranges from Samir to Pala in the valley. These create the condition of thermal inversion in the valley.
- Due to the local temperature difference of the surface in the path of the permanent wind, many types of local winds are generated, which have different names.
- Loo in North India, Sirocco originating from Northern Sahara to Europe, Khamsin in Midd, Simoon from Arabia, Brickfielder from New South Wales (Australia) brickfielders) and the Santa Ana in California is some examples of local dry winds.
- Similarly, fohn or foehn in southern Europe, bora, mistral, harmattan running from the Sahara in winter, blizzards in North America, Buran in Siberia, in Argentina The pampero and puna in the Andes are examples of some cold local winds.
- It is a hot and dry local wind of the Ganges-Indus plain that blows from west to east during summer.
- The temperature of the high-speed heat wave reaches 40°-50°C and people become affected by it. People prefer to stay indoors in the afternoon to avoid the scorching heat of the heatwave.
Fawn and chinook
- These are hot winds descending across the Alps and the Rockies, respectively. Descending from the mountain to the plain, they heat up due to pressure and raise the air temperature by 3 °C and 6 °C respectively.
- The Chinook's sphere of influence is much wider than that of the Fawn. Due to these two winds, snow starts melting in their area of effect, which facilitates agricultural work, so they are important from an economic point of view.
- Animals also get the facility to graze and the grapes start ripening soon. This warm air comes from the Sahara desert to the plains of Europe, but now observations have shown that it expands when it rises in the Southern Alps and cools and sheds its moisture in the form of rain or snow.
- When this wind crosses the mountain and descends towards the north, then the temperature starts rising again and it becomes hot.
Bora and Mistral
- These are cold and dry winds descending in the valleys of the mountainous region. The Bora runs north of the Adriatic Sea, northern Scandinavia, the northern coast of the Black Sea, and Japan in winter.
- Mistron is a fast-moving cold wind in the Rhone Valley of France that blows in the winter and brings the temperature below freezing point.
Harmattan and Sirocco
- These are the hot and dusty winds of the Sahara. When Harmattan reaches the coast of Guinea, it brings great relief to the people suffering from the humidity of the equatorial climate there.
- People consider it to be the healthiest air and call it 'doctor'. The synonym of doctor in the local language is 'Harmattan'.
- This air expands more in summer than in winter. The accompanying dust causes the entire atmosphere to become foggy or hazy.
- Sirocco runs from the Sahara to the Mediterranean. It becomes humid when it crosses the Mediterranean Sea.
- Continuous movement for a day or two causes great damage to the grapevines of Italy and Sicily because that is the time for them to flower.
Major local winds of the world
||Nature of wind
|Chinook (Snow eaters)
||Hot, dry wind
||The Rockies mountains
||Hot, dry wind
||Hot, dry wind
||Hot, moist wind
||Sahara to the Mediterranean Sea
||Hot, moist wind
||Sahara to the Iberian Peninsula
|Harmattan (Guinea Doctor)
||Hot, dry wind
||Cold, dry wind
||Blows from Hungary to North Italy
||The Alps and France
||Cold dry wind
||The western side of Andes Mountain
|Karaburun (black storm)
||Hot dusty wind
||Dust-laden dry wind
||Saharan Air Layer across the Canary Islands
||Moist wind in monsoon
High-level wind circulation
- High-level winds revolve around the whole earth by becoming east and west in a true sense. Over low latitudes, they move east and follow the thermal equator. Their speed is very fast which is called the jet stream.
- Earth's rotation is the main reason for its origin. Above the equator, maximum movement occurs in the atmosphere, due to which the rising air current goes up and spreads towards north and south.
- These air currents approach the latitudes of about 30° and become 'subtropical jet air currents'. Their speed ranges from 100 to 200 km. Happens hourly.
- Their belts are 100 to 200 km. wide and 2 to 3 km. are thick. Their position is 10 km from the ground. is at altitude.
- Apart from the subtropical jet air stream, other jet streams move away from the mid-latitudes towards the polar region. Its origin is due to temperature differences.
- It is closely related to the polar front. They are more variable. The direction of this subpolar jet air current is from west to east, that is, the wind blows from the west throughout the year. The wind speed is fastest near both the poles, due to which the condition of whirlpools arises there.
- Information about jet streams came during the Second World War when there was a suggestion to drop bombs by raising aircraft to the highest altitude. Full information regarding these jet streams has not yet been received, but research is going on.
- It is so certain that these jet streams are helpful in generating cyclones, anticyclones, and severe storms. Our pilots can save time and money by using these to fly.
- That large part of the air in the atmosphere is called air mass. Whose expansion is hundreds of thousands of square km. up to and in which the conditions of temperature and humidity are uniform horizontally at different altitudes.
evolution of air
- The development of an air mass occurs only when the air remains calm over a large area (continental or oceanic part) for a sufficiently long time so that the temperature and humidity conditions of the air and the conditions of the ground below can be established.
- This means that the different layers of the air, whose condition is the same everywhere, it is necessary to remain on the surface of the same condition for a long time.
- For the development of the air mass, it is also necessary to descend on a large scale from the top to the bottom of the air on its source area.
origin of air
- From the surface or the surface itself, the air sign possesses the properties of temperature and humidity. Such areas of the same position on the surface, where air signs arise, are called sources/origin zones/origin zones of air signs.
cold air mass and warm air mass
- If the air mass remains stationary in its source area for a long time, then it acquires the thermal and hygroscopic properties there.
- If it moves forward, then assumes the above conditions of the transmission zone, then it will be called Vayu Rashi.
- Conversely, if the temperature of the air mass is less than the temperature of that area, then that air mass is called cold or cold air mass.
- Conversely, if the temperature of the air mass is higher than the temperature of that area, then that air mass is called warm or hot air mass.
- They are marked with T or P on the seasons. (T for Tropical Air Masses and p for Polar Ones) The two types of landforms that originate from above are continental (c) and oceanic (m) (C for Continental and M for Oceanic or Maritime).
- If the polar air mass is generated over the ocean then it is marked as mP and if it is generated over the continent it is marked as cP.
- A third letter is added at the end to indicate whether the air is cooler (K) or warmer (W) than the surface passing through.
- Therefore, if a polar continental air mass is passing over a land that is warmer than it, then cPW has to be written to tell it.
- The air sign of the Arctic region is of the first type and that of the Sahara region is of the second type.
- Air masses are placed under these two classes on the basis of temperature-
- polar air and
- tropical air.
- Again these two are divided into two categories-
- Continental polar air mass and oceanic polar air mass
- continental tropical air mass and oceanic tropical air mass
- Humidity is high in the ocean air masses, which allows precipitation. Due to the dryness of the continental air masses, there is little rainfall.
- Two air masses that differ from each other in temperature and humidity cannot mix. They are separated from each other by a sloping boundary. Such a boundary is called a front.
- When two different air masses converge, a wide transitional zone is established between them.
- This is called the frontal zone or area of frontogenesis. There is no front line but a fairly wide area (from 5 to 80 km).
The polar atmosphere theory
- The front end of moving air is called the front. In the first quarter of the 20th century, Norwegian meteorologist V. Birkenes and his son Jacob Birkenes presented the polar theory of the origin of temperate cyclones.
- This principle proved useful for giving weather forecasts and for the interpretation and prediction of weather. According to this theory, the origin of a temperate cyclone occurs in the following six phases-
- In this state, the warm air mass and the cold air mass are located parallel to each other and the atmosphere is almost calm.
- This is called the initial stage of the cyclone. In this stage, the warm air mass starts rising and the cold air mass moves towards the warm air mass.
- This is called the youth stage of the cyclone. At this stage, the wind-weight lines of the cyclone start becoming circular.
- In this stage, the hot and cold air masses come closer to each other.
- In this stage, the hot and cold air signs mix.
- In this stage, the warm region disappears completely and the cyclone develops completely and starts moving forward.
Humidity and Precipitation
भ्रष्टाचार निवारण अधिनियम, 1988 क्या है?
What is Cyclone? and Anticyclone
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