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Atmospheric phenomena like temperature, pressure, rain and wind are essential for the existence of life on the earth. Since the axis of the earth is tilted at an angle of 231/2°, solar energy received on the surface of the earth is not always uniform. Difference in temperature causes difference in pressure. This leads to change in the direction and velocity of winds. Winds that blow in different directions with different velocity considerably influence human life. The position of continents and oceans determine the nature of winds. Thus this unit discusses different atmospheric phenomena, the winds that cause due to these phenomena and the influence of these winds in human life.
→ Atmospheric pressure : The weight of atmospheric air.
→ Mercury barometer : The instrument used for the measurement of atmospheric pressure.
→ Hecto Pascal (hPa)/ millibar : The unit used for the measurement of atmospheric pressure.
→ The factors influencing atmospheric pressure : Temperature, altitude of a place, humidity.
→ Humidity: The quantity of water vapour present in the atmosphere.
→ Isobars: Imaginary lines drawn on maps joining places having the same atmospheric pressure.
→ Global pressure belts : Generally the earth experiences the same atmospheric pressure between certain latitudes. Those latitudinal zones are called global pressure belts.
→ Horse latitudes: The subtropical high pressure belt in the Atlantic ocean devoid of winds are known as horse latitudes.
→ Doldrum : The low pressure region about 5°N and 5°S of the equator characterised by feable wind is called doldrum.
Sslc Geography Chapter 2 Pdf
→ Wind : The horizontal movement of air from a high pressure zone to a low pressure zone is called wind.
→ The factors that influence the speed and direction of winds : Pressure gradient, Coriolis force and friction.
→ Coriolis force : Due to the force generated as a result of the rotation of the earth, any freely moving body on the earth’s surface gets deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
→ Ferrel’s Law : The law formulated by Admiral Ferrel on the deflection of winds under the influence of Coriolis force.
→ Planetary winds: The winds developed between global pressure belts and blow in the same direction throughout the year are called planetary winds.
→ Trade winds : The steady winds that blow continuously from subtropical high pressure belts to equatorial low pressure belt.
→ Westerlies: Winds that blow continuously from subtropical high pressure belts to subpolar low pressure belts.
→ Polar winds: Winds that blow from polar high pressure belts to subpolar low pressure belts.
→ Periodic winds : Winds that repeat at regular intervals of time and can be seasonal or diurnal.
→ Monsoon winds : Winds that change the direction with change in seasons.
→ Land breeze/ sea breeze : Winds that cause as a result of the unequal heating and cooling of land and sea and the resultant pressure change. Valley breeze : Winds that blow from valleys to the mountain tops during the day.
→ Mountain breeze: Winds that blow from the mountain tops to valleys during the night.
→ Local winds : Winds formed as a result of the local differences in atmospheric pressure.
→ Variable winds: Winds with entirely different characteristics formed during certain atmospheric situations.
→ Cyclones : A low atmospheric pressure at centre surrounded by high pressure regions with strong whirlwinds blowing.
→ Anticyclones : Phenomenon where strong whirl winds blow from high pressure centre to, the surrounding low pressure areas.
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Hss Live Guru 8th Hindi Kerala Syllabus प्रश्ना 1.
कहानी का कौन-सा प्रसंग शीर्षक को सार्थक बनाने में अधिक संगत है?
उत्तर:
कहानी का यह अंतिम प्रसंग शीर्षक को सार्थक बनाने में अधिक संगत है। यहाँ लेखक के पूछने पर अंधा व्यक्ति कहता है कि रात में लोग प्रकाश के बिना निकलते हैं। वे आकर हमसे टक्कर लेते हैं। उनसे बचने तथा उन्हें प्रकाश देने के लिए हम लालटेन लेकर चलते हैं। मतलब स्वयं अंधे होते हुए भी वे लालटेन से दूसरों को राह दिखाते हैं। यह प्रसंग ‘उजाला’ शीर्षक को सार्थक बनाने योग्य है।
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Answer the following. Score 1 each.
Choose the correct answer.
Sslc Social Science Important Questions Question 1.
The instrument used to measure atmospheric pressure.
Anemometer
Mercury barometer
Thermometer
Wind Vane
Answer:
Mercury barometer
Question 2.
The unit used to measure atmospheric pressure.
Millibar
Milligram
Millimeter
Celsius
Answer:
Millibar
Question 3.
The quantity of water vapour in atmospheric air.
Pressure gradient
Humidity
Dew
Density
Answer:
Humidity
Question 4.
The pressure belt where sun rays fall vertically throughout the year.
Subpolar low pressure belt
Subtropical high pressure belt
Equatorial low pressure belt
Polar high pressure belt
Answer:
Equatorial low pressure belt
Question 5.
The basis for the formation of global pressure belts
Temperature
Altitude
Rotation of the earth and the variations in the amount of solar energy
None of these
Answer:
Rotation of the earth and the variations in the amount of solar energy
Question 6.
Which of the following does not influence the speed and direction of winds’?
Pressure gradient
Friction
Altitude
Coriolis force
Answer:
Altitude
Question 7.
Winds that blow from subtropical high pres-sure belts to equatorial low pressure belt.
Trade winds
Polar easterlies
Westerlies
Periodic winds
Answer:
Trade winds
Question 8.
Monsoon winds are
planetary winds
local winds
periodic winds
variable winds
Answer:
periodic winds
Question 9.
The wind known as ‘snow eater ’
Chinook
Loo
Harmattan
Foehn
Answer:
Chinook
Question 10.
The hot dry winds that blow towards the southern valleys of the Alps mountains
Mistral
Chinook
Foehn
Loo
Answer:
Foehn
Question 11.
A low atmospheric pressure at the centre surrounded by high pressure regions
Cyclone
Anticyclone
Trade wind
Periodic wind
Answer:
Cyclone
Answer in a sentence.
Question 1.
The winds that helped Vasco da Gama to travel from Malindi port to Calicut port.
Answer:
Southwest monsoon winds.
Question 2.
What is the basic reason for the formation of winds. ‘
Answer:
Pressure differences over different latitudinal zones at the global level.
Question 3.
What is atmospheric pressure?
Answer:
The weight of atmospheric air on the earth’s surface.
Question 4.
What is average weight exerted by air on the earth’s surface?
Answer:
1034 mg per cm2
Question 5.
What is the rate at which atmospheric pressure decreases as height increases’?
Answer:
At the rate of 1 millibar per an altitude of 10 m.
Question 6.
When we go to high altitude places like Ootty, we feel clogging of ear. Why?
Answer:
Question 7.
Which pressure belt was a nightmare to ancient mariners? Why?
Answer:
Question 8.
Equatorial low pressure belt with feeble winds is also known by another name. Which is that
Answer:
Question 9.
What is the reason for the low pressure experienced in the equatorial regions’?
Answer:
Since sun rays are always vertical here, air expands and rises vertically. This is the zone where the sun’s rays fall vertically throughout the year.
Question 10.
Which pressure belt is known as Horse latitude?
Answer:
Subtropical high-pressure belt.
Question 11.
Why is low pressure experienced in the subpolar regions’?
Answer:
Cold air is thrown up due to the rotation of the earth.
Sslc Social Chapter Wise Questions And Answers Question 12.
With the apparent movement of the sun, the shifting of pressure belt is more vivid in Northern Hemisphere. Why?
Answer:
Presence of continents/landmasses.
Question 13.
The westerlies are stronger in the Southern Hemisphere than in the Northern Hemisphere. Why?
Answer:
Presence of vast oceans in the Southern Hemi-sphere.
Question 14.
Polar winds are known as polar easterlies. Why?
Answer:
Due to Coriolis force, polar winds blow from the east in both the hemispheres.
Question 15.
Who was the first to observe the shift in the direction of monsoon winds?
Answer:
Hippalus, the Arab scholar.
Question 16.
Name the winds formed as a result of the defection of south-east trade winds due to Coriolis effect.
Answer:
Southwest monsoon winds.
Question 17.
Name the winds formed when northeast trade winds get strengthened.
Answer:
Northeast monsoon winds.
Answer the following. Score 2 each.
Question 1.
What are the factors influencing atmospheric pressure? How are they related to atmospheric pressure?
Answer:
The factors influencing atmospheric pressure are temperature, altitude and humidity.
Temperature, altitude and humidity are inversely proportional to atmospheric pressure. As temperature, altitude and humidity increase, pressure decreases. In other words, as temperature, altitude and humidity decrease, pressure increases.
Question 2.
The atmospheric pressure decreases with altitude. Why? Write the rate at which atmospheric pressure decreases.
Answer:
Question 3.
Mountaineers carry oxygen cylinders with them. Why?
Answer:
As height increases, the amount of air decreases. So required amount of air will not be available at high altitudes.
Question 4.
The weight exerted by air on earth’s surface is the atmospheric pressure, but atmospheric pressure is not experienced uniformly all over. Why?
Answer:
Temperature, altitude and humidity are the factors that influence pressure.
The variations in the distribution of temperature due to the spherical shape of the earth and the tilting of earth’s axis, difference in the altitude of regions and the variations in humidity influence pressure.
Question 5.
What is the relation between humidity and atmospheric pressure?
Answer:
The quantity of water vapour present in the atmosphere is called humidity. Humidity and atmospheric pressure are inversely proportional. Increase in the quantity of water vapour in a unit volume of air leads to decrease in atmospheric pressure.
Question 6.
Equatorial low pressure belt is also known as Doldrum. Why?
Answer:
Equatorial low pressure belt is situated between 5°N and 5°S. As the air in this zone ascends on a large scale due to high temperature, winds are very feeble here. So it is called Doldrum meaning the zone with no winds.
Question 7.
Though the air in subpolar regions is cold, low pressure is experienced here. Why?
Answer:
Though the cold air in subpolar regions remain close to the earth, the air is thrown up due to earth’s rotation. As the amount of air decreases, low pressure is experienced in the subpolar regions.
Question 8.
How does pressure gradient influence the speed of wind?
Answer:
The pressure gradient is said to be steeper when the pressure difference is more. In such places the speed of wind will be high also.
Question 9.
What is Coriolis force?
Answer:
Due to the earth’s rotation, freely moving bodies on the earth’s surface get deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This is known as Coriolis force. This was detected by the French mathematician Gustav Coriolis.
Question 10.
What is Ferrel’s law?
Answer:
Admiral Ferrel, an American scientist found out that the winds in the Northern Hemisphere deflect towards their right and those in the Southern Hemisphere deflect towards the left due to the Coriolis effect Which increases from equator to the poles. The law put forward by him on the basis of this is known as Ferrel’s law.
Question 11.
How does friction influence the speed of winds?
Answer:
The speed of wind will be high over ocean surfaces and level lands as the friction is less.
The friction is more along difficult terrains and places with dense forest cover. The speed of wind will be less in those places.
Question 12.
Polar winds are called Polar easterly winds. Why?
Answer:
Polar winds are the cold winds that blow from polar high pressure belts to subpolar low pressure belts.
Due to Coriolis force, polar winds in both the hemispheres blow from the east.
Question 13.
When we travel up to Ooty or Kodaikanal, we experience clogging of ears and slight breathing difficulty. Why?
Answer:
It is because of low pressure in high altitude regions. Altitude of a place determines change in atmospheric pressure. Ooty and Kodaikanal are high-altitude regions. We experience discomfort while traveling up to high altitude regions because it takes some time for our body to adjust to the difference that happens to atmospheric pressure. Due to this we experience clogging of ears and slight breathing difficulty.
Question 14.
In what way would equatorial region and polar regions experience atmospheric pressure?
Answer:
Question 15.
Air in coastal regions would show a higher humidity in comparison with that of inland areas. What could be the reason?
Answer:
Nearness to water body is the main reason. Coastal regions have high humidity due to nearness to water body. Inland regions are away from water bodies and have less humidity.
10th Social Science Important Questions Question 16.
Identify the following winds from the given hints.
a. Blow from subtropical high pressure belts to equatorial low pressure belt.
b. Blow from subtropical high pressure belts to subpolar low pressure belts.
c. Blow from polar high pressure belts to subpolar low pressure belts.
d. Blow from sea to land during day time.
Answer:
a. Trade winds
b. Westerlies
c. Polar winds
d. Sea breeze
Question 17.
The following are the features of some local winds. Identify them.
a. Since this wind reduces the severity of the cold, it is helpful for wheat cultivation in the Canadian Shields.
b. Causes a rise in the summer temperature of North Indian plains.
c. As the air heats up due to pressure from the descent, it helps in reducing the severity of cold in that region.
d. Improves the climate of West Africa.
Answer:
a. Chinook
b. Loo
c. Foehn
d. Harmattan
Question 18.
Explain:
High pressure
Low pressure
Answer:
High pressure:
If the atmospheric pressure of an area is higher than that of the surrounding regions, it can be designated as high pressure.
Low pressure:
If the atmospheric pressure of an area is less than that of the surrounding regions, it can be designated as low pressure.
Question 19.
Identify the following local winds.
a. A dry wind which blows from Sahara desert towards the West Africa.
b. The wind that blows towards the southern valleys of the Alps.
Answer:
a. Harmattan
b. Foehn
Question 20.
Arrange the columns suitably.
| A | B |
| Sea breeze | Summer |
| Mountain breeze | Winter |
| South west monsoon wind | Day |
| North east monsoon wind | Night |
Answer:
| A | B |
| Sea breeze | Summer |
| Mountain breeze | Winter |
| South west monsoon wind | Day |
| North east monsoon wind | Night |
Question 21.
The equatorial low pressure region was a nightmare for the ancient mariners. Why?
Answer:
Question 22.
What are the variable winds? Give example.
Answer:
Winds with entirely different characteristics formed during certain atmospheric situations, e.g. Cyclones.
Answer the following. Score 3 each.
Question 1.
Choose the correct pair.
Factors Pressure
i. Temperature increases Increases
ii. Humidity decreases Decreases
iii. Altitude increases Increases
iv. Humidity increases Decreases
v. Temperature decreases Increases
vi. Altitude decreases Increases
A. i, ii, iii
B. ii, iv, v
C. i, ii, iii
D. iv, v, vi
Answer:
D. iv, v, vi
Question 2.
Temperature and pressure are inversely proportional. Explain.
Answer:
Air expands when it gets heated. The expanded air is less dense and hence it ascends. This results in lowering of atmospheric pressure.
The ascending air spreads to the sides and cools. On cooling, it becomes dense and descends. As a result, atmospheric pressure increases.
As temperature increases, pressure decreases and as temperature decreases, pressure increases.
Question 3.
Write the three basic reasons for the forma¬tion of global pressure belts.
Answer:
Question 4.
Explain with examples that the peculiarities of the source regions influence the nature of wind.
Answer:
Question 5.
What are the factors that influence the speed and direction of winds?
Answer:
Question 6.
Why do trade winds blow from northeast and southeast directions?
Answer:
Trade winds blow from subtropical high pressure belts to equatorial low pressure belt.
Due to Coriolis force, these winds get deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. As a result, they blow towards west.
Thus trade winds blow from northeast in the Northern Hemisphere and southeast in Southern Hemisphere.
Question 7.
Westerlies are described as ‘Roaring Forties ‘Furious Fifties ’ and ‘Shrieking Sixties ’ in the Southern Hemisphere. Why?
Answer:
Question 8.
The diagrammatic representation of some winds is given. Identify and name the winds.
Answer:
B – Westerlies in Northern Hemisphere.
C – Trade winds in North-South Hemispheres.
Question 9.
The following are the characteristics of planetary winds. Identify to which wind they are related.
Hints: Trade winds, Westerlies, Polar winds Correct direction of planetary winds
| Characteristics | Planetary winds |
| a. Blow strongly in the Southern Hemisphere b. Have a role in determining the climate of North America c. Blow in the north east direction d. Also called easterly wind e. Wind direction from west f. Blow from subtropical high pressure belts to equatorial low pressure belt | ……………………………. ……………………………. ……………………………. ……………………………. ……………………………. |
Answer:
a. Westerlies
b.Polar winds
c. Trade winds
d. Polar winds
e. Westerlies
f. Trade winds
Question 10.
The following are the factors influencing pres-sure. How do they affect pressure?
Temperature
Altitude
Humidity
Answer:
| Factors | Increase | Decrease |
| Temperature | Pressure decreases | Pressure increases |
| Altitude | Pressure decreases | Pressure increases |
| Humidity | Pressure increases | Pressure decreases |
Question 11.
Write the factors for the occurrence of monsoon winds.
Answer:
Question 12.
Match the columns suitably.
| A | B |
| Trade winds in northern hemisphere | South east wind |
| Trade winds in southern hemisphere | Monsoon wind |
| Coriolis effect in northern hemisphere | North west wind |
| Westerlies in southern hemisphere | North east wind |
| Periodic wind | To the right |
| Coriolis effect in southern hemisphere | To the left |
Answer:
| A | B |
| Trade winds in northern hemisphere | North east wind |
| Trade winds in southern hemisphere | South east wind |
| Coriolis effect in northern hemisphere | To the right |
| Westerlies in southern hemisphere | North west wind |
| Periodic wind | Monsoon wind |
| Coriolis effect in southern hemisphere | To the left |
Question 13.
Find out an example for local wind in India. Write its features.
Answer:
Loo, a hot dry wind blowing in the North Indian plain
Features
Question 14.
Which are the Statements related to trade winds?
a. Blow from sub tropical high pressure belt to subpolar belts.
b. Blow from east direction to equatorial regions
c. Blow from east direction to subpolar belts
d. Blow towards equator in both hemispheres
e. Winds that converge at Intectropical zone.
i. a, b, c
ii. b, d, e
iii. b, c, e
iv. c, d, e
Answer:
ii. b, d, e
Question 15.
A. Mountain breeze
B. Valley breeze
Based on the features of the above winds answer the following questions,
a. Which wind blows during day time, A or B?
b. From where to where is the direction of wind during night time?
c. How is valley breeze formed?
Answer:
a. Valley Breeze occurs during day time, ie, B.
b. Mountain breeze formed during night blows towards the valley.
c. During the day time, the air in the valley gets heated up more than the air on the mountain top. As a result, the wind blows upslope from the valley. This is valley breeze.
Question 16.
i. The planetary winds that blow from subtropical high pressure belts to subpolar low pressure best are called westerlies. Why?
ii. These winds are stronger in the Southern Hemisphere. Why?
iii. By what other names are these winds known?
Answer:
i. The direction of these winds are mostly from the west.
ii. Due to the vast expanse of oceans in the South- em Hemisphere,
iii. Roaring Forties: along 40° latitudes
Furious Fifties: along 50° latitudes
Shrieking sixties: along 60° latitudes
Question 17.
Observe the pictures and answer the questions.
i. Which diagram represents low pressure region? Substantiate your answer.
ii. What is the name by which the smooth curved lines in the diagrams are known? What does it indicate?
Answer:
i. Diagram B represents low pressure region.
The value of isobars decreases towards the centre.
ii. Isobars These are imaginary lines joining places having equal atmospheric pressure.
Question 18.
Is the atmospheric pressure the same at all places given below? Write a note based on the factors influencing the atmospheric pressure.
Central Pacific region
Ootty
Polar region
Answer:
The factors influencing the atmospheric pressure are temperature, altitude and humidity. All these factors are inversely proportional to pressure.
Central Pacific region: As this is equatorial region, high temperature and high humidity are experienced. So low pressure is the result.
Ooty: As situated above sea level, there is a ratification of air and so the pressure is low.
Polar region: Since the sunrays are slanting, low temperature and high pressure.
Question 19.
Write the reason. .
i. The atmospheric pressure is low in the coastal regions and high in the interior regions.
ii. Low pressure is experienced throughout the year in the equatorial regions.
iii. Compared to plains, there is a decrease in the atmospheric pressure in the mountains.
Answer:
i. Difference in humidity. Humidity is the amount of water present in the atmosphere. If the quantity of water vapour is more in a unit volume of air, the atmospheric pressure will be less. Coastal regions have high humidity due to the nearness to waterbodies. So the pressure is low. But the interior regions experience high pressure as they are away from water bodies.
ii. Due to temperature. Sunrays fall vertically throughout the year in the equatorial regions. As the temperature is high, the air expands and rises up on a massive scale. As a result, low pressure is experienced.
iii. Difference in altitude. As height increases, atmospheric pressure decreases. The amount of air is less in the mountainous regions. This results in low pressure.
Answer the following. Score 4 each.
In Search Of The Source Of Wind Important Questions Question 1.
Write a note on monsoon winds.
Or
Analyse the role of trade winds in the occurrence of south west monsoon winds and north east monsoon winds.
Answer:
Winds that change their direction according to change in season are called monsoon winds.
Monsoon winds are formed due to the apparent movement of the sun, Coriolis force and differences in heating.
Sun’s rays fall vertically to the north of the equator during certain months due to the tilt of the earth’s axis. This leads to an increase in temperature along the region through which Tropic of Cancer passes. The pressure belts
also shift slightly northwards in accordance with this.
The south east trade winds cross the equator and move towards the north. As the trade winds cross the equator, they get deflected and transform into south west monsoon winds under the influence of the Coriolis effect. The low pressure formed over the land due to the intense day temperature attracts these sea winds and further contributes to the formation of south west monsoon winds. As a result of the formation of high pressure zones over the Asian landmasses during winter and low pressure zones over the Indian Ocean, the north east trade winds get strengthened. These are the north east monsoon winds.
Question 2.
Write the difference between land breeze and sea breeze.
Answer:
During day time, the land gets heated up quickly. As a result, the air in contact with the land also gets heated. This leads to the formation of low pressure over the land which causes comparatively cooler air to blow from the sea. This is known as sea breeze.
As the land cools faster than the sea during the night, it would be high pressure over the land and low pressure over the sea. This results in the movement of air from the land to sea. This is the land breeze.
Question 3.
Based on the hints given, identify the pressure belts.
a. The zone where sun rays fall vertically throughout the year.
b. Also known as Horse latitude.
c. The zones where low pressure are formed due to the rotation of the earth even though the air masses here are very cold.
d. The zones that experience severe cold throughout the year.
Answer:
a. Equatorial low pressure belt
b. Subtropical high pressure belt
c. Subpolar low pressure belts
d. Polar high pressure belts
Question 4.
Based on the given hints, identify the basic reasons for the formation of the pressure belts.
Hints: Amount of solar energy, rotation of earth
| Pressure belts | Reasons for formation |
| Equatorial low pressure belt | a …………………………… |
| Subtropical high pressure belts | b …………………………… |
| Subpolar low pressure belts | c …………………………… |
| Polar high pressure belts | d …………………………… |
Answer:
a. Amount of solar energy
b. Rotation of earth
c. Rotation of earth
d. Amount of solar energy.
Question 5.
‘Global variation in the atmospheric pressure lead to the formation of winds ’. Explain this statement relating it with the formation of planetary winds.
Answer:
The horizontal movement of air form high pressure regions to low pressure regions is called wind. Steady winds blow from subtropical high pressure belts to equatorial low pressure belts (trade winds) and from subtropical high pressure belts to subpolar low pressure belts (westerlies).
Similarly, polar winds blow from polar high pressure belts to subpolar low pressure belts. Due to the variations in the distribution of solar energy received and the rotation of the earth, variations occur in the pressure belts formed. This is the reason for the formation of winds.
Question 6.
Write to which winds the following characteristics are related.
a. Blow from the east in both the hemispheres due to Coriolis force.
b. Blow strongly over the oceans of Southern Hemisphere.
c. Blow constantly towards equatorial low pressure belt.
d. Play a significant role in determining the climate of North America, North European countries and Russia.
Answer:
a. Polar winds
b. Westerlies
c. Trade winds
d. Polar winds
Question 7.
Match suitably.
| A | B |
| Winds change direction with change in season | Land breeze |
| Blow during night | South west monsoor winds |
| Blows upslopes from the valley during day. | Monsoon winds |
| Form as a result of deflection due to Coriolis force | Valley breeze |
Answer:
| A | B |
| Winds change direction with change in season | Monsoon winds |
| Blow during night | Land breeze |
| Blows upslopes from the valley during day. | Valley breeze |
| Form as a result of deflection due to Coriolis force | South west monsoor winds |
Question 8.
Complete the table on local winds over the places through which they blow.
| Local winds | Region of blow |
| a. Loo b. Chinook c. Foehn d. Harmattan | ………………………… ………………………… ………………………… ………………………… |
Answer:
a. North Indian plains
b. Eastern slopes of the rocky mountain in North America
c. Southern val leys of the Alps mountain
d. Western Africa
Question 9.
South west monsoon winds are in fact the south east trade winds that blow in the southern hemisphere. Do you agree with this? Why?
Answer:
Sun’s rays fall vertically to the north of the equator during certain months due to the tilt of the earth’s axis. This leads to an increase in temperature along the region through which Tropic of Cancer passes. The pressure belts also shift slightly northwards in accordance with this.
The south east trade winds cross the equator and move towards the north. As the trade winds cross the equator, they get deflected and transform into south west monsoon winds under the influence of the Coriolis effect. The low pressure formed over the land due to the intense day temperature attracts these sea winds and further contributes to the formation of south west monsoon winds.
Question 10.
The given statements are related to two global pressure belts. Name them.
a. Extends up to about 5° N, 5° S of the equator.
b. Extends approximately over 30°N and 30°S.
c. Trade winds and westerlies blow from either side of this pressure belt.
d. Known as doldrum.
Answer:
a. Equatorial low pressure belt.
b. Subtropical high pressure belts.
c. Subtropical high pressure belts.
d. Equatorial low pressure belt.
Question 11.
Answer the questions based on the figure.
a. Globally, how many high pressure belts and low pressure belts are there?
b. What is the latitudinal extent of each pres-sure belt?
c. Equatorial regions experience low pressure throughout the year. Why?
Answer:
a. There are four high pressure belts and three low pressure belts globally.
b.
c. Equatorial regions experience high temperature throughout the year. Due to this, the air expands and rises vertically, resulting in low pressure.
Question 12.
Which are the pressure belts on either side of subtropical high pressure belts. Write notes on the winds formed from this pressure belt in the Northern Hemisphere. Which of these winds is most influenced by the Coriolis force?
Answer:
Trade winds
Westerlies
Question 13.
Observe the picture and answer the questions.
a. Which is the periodic wind marked in the picture?
b. In which season does it blow?
c. Why do these winds blow form Indian Ocean to Indian subcontinent?
d. In which direction do these winds blow? Why?
Answer:
a. Monsoon wind: South west monsoon wind.
b. During summer season of Northern Hemisphere.
c. Low pressure is formed over Indian subcontinent due to the intense day temperature. The Indian Ocean regions remain as high pressure during this time. So these winds blow from the Indian Ocean to Indian subcontinent.
d. South west monsoon winds blow from sea to land. The difference in pressure over land and sea is the reason.
Question 14.
Distinguish between mountain and valley breeze.
Answer:
Valley breeze: During day time, the air in the valley gets heated up more than the air on the mountain tops. As a result, the wind blows upslope from the valley. This is known as valley breeze.
Mountain breeze: During night, the air in the mountainous regions cools due to the intense cold conditions in that region. As cool air is denser, it blows towards the valley. This is known as mountain breeze.
Question 15.
Distinguish between cyclones and anticyclones.
Answer:
Cyclones are caused by the formation of low atmospheric pressure at the centre surrounded – by high pressure regions. Strong whirl winds blow towards such low pressure centres from the surrounding high pressure areas. Due to Coriolis effect, winds flow in the anticlockwise direction in the Northern Hemisphere and clockwise direction in the Southern Hemisphere.
Anticyclones are phenomenon where strong whirl winds blow form the high pressure centres to the surrounding low pressure areas. Due to Coriolis effect, the pattern of wind is anticlockwise in Southern Hemisphere and clockwise in Northern Hemisphere.
Answer the following. Score 5 or 6 each.
Question 1.
Observe the picture an answer the questions.
i. Which are the pressure belts indicated by the letters A. B, C and D in the picture?
ii. How are the pressure belts A and B formed? Hi. Which are the planetary winds formed in these pressure belts? Write their features also.
i. A: Equatorial low pressure belt
B: Subtropical high pressure belt
C: Subpolar low pressure belt
D: Polar high pressure belt
ii. Equatorial low pressure belt This is the zone where the sun’s rays fall vertically throughout the year. Hence the temperature will be high in this zone all through the year. The air expands due to sun’s heat and rises up on a massive scale. So low pressure is formed here.
Subtropical high pressure belt The hot air ascending from the equatorial low pressure belt cools gradually and subsides at the subtropical zone due to the rotation of the earth. This is the reason for the formation of high pressure in this zone.
iii. Trade winds: The winds blowing continuously from subtropical high pressure belt to equatorial low pressure belt. As the winds blow from north east in this zone, they are known as north east trade winds.
Westerlies: The winds blowing continuously from subtropical high pressure belt to subpolar low pressure belt. The direction of these winds is from south-west. These winds are mostly influenced by Coriolis force.
Polar winds: Winds blowing from polar high pressure belt to subpolar low pressure belt. These winds blow from the east due to the Coriolis force.
Question 2.
Planetary winds influence global climate.
i. Substantiate this statement based on the influence of trade winds in the formation of monsoon winds.
ii. Write the pressure belts of northern hemisphere and the winds blowing between them.
Answer:
i. The north east trade winds blowing in the northern hemisphere and the south east trade winds blowing in the southern hemisphere lead to the formation of monsoon winds. Monsoon winds are winds that change direction in accordance with season. Monsoon is the seasonal reversal of wind in a year.
The factors responsible for the formation of monsoon winds are the apparent movement of the sun, Coriolis force and difference in heating. During the summer in the Northern Hemisphere, high temperature is experienced along the region through which the Tropic of Cancer passes. The pressure belts shift slightly northwards. The south east trade winds also cross the equator and move towards the north.
As the trade winds cross the equator, they get deflected and transfer into south west monsoon winds under the influence of the Coriolis effect. The low pressure formed over the land due to the intense day temperature attracts these sea winds and further contributes to the formation of south west monsoon winds. As a result of the formation of high pressure zones over the Asian landmass during winter and low pressure zones over the Indian Ocean, the north east trade winds get strengthened. These are the north east monsoon winds.
ii. Global pressure belts in the northern hemisphere.
Question 3.
Variations in atmospheric pressure occur in accordance with the variations in temperature, altitude and humidity experienced in a region. Explain how atmospheric pressure is related to these factors.
Answer:
The weight exerted by air on the earth’s surface is called atmospheric pressure. The variations in the density of air bring about variations in weight of air and thereby variations in atmospheric pressure. Temperature, altitude and humidity are inversely proportional to atmospheric pressure.
Temperature and atmospheric pressure :
Air expands when gets heated up. The expanded air is less dense and hence it ascends. This leads to lowering of atmospheric pressure. The ascending air spreads to the sides and cools. It becomes dense and decends. This results in sinking of cold air. As a result, atmospheric pressure increases. Thus as temperature increases, pressure decreases and as temperature decreases, pressure increases. Thus temperature and atmospheric pressure are inversely proportional.
Altitude and atmospheric pressure: The atmospheric pressure decreases with altitude. The pressure decreases at the rate of 1 millibar per an altitude of 10 metres. The ratification of air with altitude is the reason for the decrease in atmospheric pressure.
Humidity and atmospheric pressure: The quantity of water present in atmospheric air is called humidity. Water vapour is lighter than air and hence it ascends. If the quantity of water vapour is more in a unit volume of air, then naturally the atmospheric pressure will be less. Thus humidity and atmospheric pressure are also inversely proportional.
Question 4.
Explain about Global pressure belts.
Answer:
The atmospheric pressure is uniform between certain latitudes. Based on that the earth’s surface is divided into different pressure belts. These are known as global pressure belts.
Equatorial low pressure belt: This pressure belt extends upto 5°N and 5°S of the equator. This is the zone where the sun’s rays fall vertically throughout the year. Hence the temperature will be high in this zone all through the year. The air expands due to sun’s heat and ascends on a massive scale. This is the reason for the formation of low pressure here. As the air in this zone ascends on a large scale, winds are feeble here. This pressure belt is also known as Doldrum, meaning the zone with no winds.
Subtropical high pressure belts: Subtropical high pressure belts extend about 30°N and 30°S. The hot air ascending from the equatorial low pressure belt cools gradually and subsides at the subtropical zone due to the rotation of the earth. This is the reason for the formation of high pressure belts all along this zone. These latitudes are also known as horse latitudes.
Subpolar low pressure belts: The pressure belts formed over 60°N and 60°S are the subpolar low pressure belts. As this zone is close to the poles, the air is colder here. Though the cold air remains closer to earth, the air is thrown up due to the rotation of the earth. As a result, low pressure is experienced all along the subpolar region.
olar high pressure belts: These zones experience severe cold throughout the year. As a result, the air remains chilled under the extreme cold that prevails over the poles. This contributes to the steady high pressure experienced here.
Question 5.
The factors that influence the speed and direction of winds are pressure gradient, Coriolis force and friction. Explain.
Answer:
The horizontal movement of air form high pressure zone to low pressure zone is called wind. The pressure belts shift according to the apparent movement of the sun. The nature of wind is influenced by variations in pressure, rotation of earth and the features of the region over which it blows.
Pressure gradient:The change in pressure with horizontal distance is termed as pressure gradient. The pressure gradient is said to be steeper when the pressure difference is more. In
such places, the speed of wind will also be more.
Coriolis force: French mathematician Coriolis observed that due to a force generated as a result of the earth’s rotation, freely moving bodies get deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This is known as Coriolis force. Admiral Ferrel, an American scientist noted that as winds are free movement of air, they get deflected. Coriolis force formed as a result of earth’s rotation, deflects the winds.
Friction: Friction is something that prevents the free movement of wind. The speed of wind will be high over ocean surface and level lands as the friction is less. On the other hand friction is more along difficult terrains and places with dense forest cover. So the speed of wind will be less in those places.
Question 6.
Explain about the planetary winds.
OR
Global pressure belts pave the way for the formation of planetary winds. Explain the inter-relationship between the two.
Answer:
Pressure differences exist globally between different latitudinal zones. These pressure difference lead to the formation of winds. The winds developed between global pressure belts are called planetary winds. There are three types of planetary winds.
1.Trade winds: Trade winds are the winds blowing from subtropical high pressure belts to equatorial low pressure belt. These winds blow as north east winds in Northern Hemisphere and south east winds in Southern Hemisphere. The zone where trade winds from both the Hemispheres converge is known as Inter Tropical Convergence Zone.
2. Westerlies: The winds blowing from the subtropical high pressure belts in both the hemisphere towards the subpolar low pressure belts are called Westerlies. As they blow from the west, they are called westerlies. In the Northern Hemisphere, they blow from the south western direction to the north eastern direction. But in the Southern Hemisphere, they blow from the north western direction to the south eastern direction. Due to the presence of vast oceans in Southern Hemisphere, the westerlies are very strong here. Here they are known by different names like Roaring Forties, Furious Fifties and Shrieking Sixties.
3. Polar easterlies: Polar regions are centres of high pressure. The polar winds are cold winds that blow from polar high pressure belts to subpolar low pressure belts. Due to Coriolis force, these winds blow from the east in both the hemispheres. Hence they are called Polar easterlies. Polar winds play a significant role in determining the climate of North America, North European countries and Russia.
Question 7.
Write a note on the periodic winds.
Answer:
Periodic winds are winds that repeat at regular intervals of time and can be seasonal or diurnal.
There are three types of periodic winds.
Monsoon winds: Monsoon winds are those that undergo seasonal reversal of direction. The term monsoon has derived from the Arabic word “Mausim” meaning season. Monsoon is a phenomenon in which reversal of direction
of winds occur in a year. The main factors responsible for the formation of monsoon winds are the apparent movement of the sun, Coriolis force and differences in heating.
Sun’s rays fall vertically to the north of the equator during certain months due to the tilt of the earth’s axis. This leads to an increase in temperature along the region through which Tropic of Cancer passes. The pressure belts also shift slightly northwards in accordance with this. The south east trade winds cross the equator and move towards the north. As the trade winds cross the equator, they get deflected and transform into south west monsoon winds under the influence of the Coriolis effect. The low pressure formed over the land due to the intense day temperature attracts these sea winds and further contributes to the formation of south west monsoon winds.
As a result of the formation of high pres¬sure zones over the Asian landmasses during winter and low pressure zones over the Indian Ocean, the north east trade winds get strength¬ened. These are the north east monsoon winds.
Land breeze and sea breeze: During day time, the land gets heated up quickly. As a result, the air in contact with the land also gets heated. This leads to the formation of low pressure over the land which causes compara-tively cooler air to blow from the sea. This is known as sea breeze.
As the land cools faster than the sea during the night, it would be high pressure over the land and low pressure over the sea. This results in the movement of air from the land to sea. This is the land breeze.
Mountain breeze and valley breeze :
Mountain breeze and valley breeze are winds experienced in mountainous regions. During the day, the air in the valley gets heated up more than the air on the mountain tops. As a result, the wind blows upslope form the valley. This is called valley breeze.
During the night, the air in the mountainous regions cools due to the intense cold conditions in that region. As cool air is denser, it blows towards the valley. This is called mountain breeze.
Wind Flow Direction In Kerala Question 8.
Write a note on local winds.
Answer:
Local winds are those that are formed as a result of the local differences in atmospheric pressure. Their effects are limited to a comparatively smaller locality and are weak. These are known by different names in different parts of the world.
Loo: Hot, dry winds that blow in the afternoons in the North Indian plains in summer are called Loo. These winds blowing from Rajasthan desert cause a rise in the summer temperature of North Indian plains.
Chinook: The hot and dry winds that blow down the eastern slopes of the Rocky mountain chains of North America are called Chinook. As a result of these winds, the snow along the eastern slopes of the Rockies melts away. So they are known as “Snow eater”. As they lessen the intensity of cold, suitable for the cultivation of wheat in the Canadian lowlands.
Foehn: The hot dry winds that blow towards the southern valleys of the Alps mountains are called Foehn. As the air heats up due to pressure from the descend, it helps in reducing the severity of cold in that region.
Harmattan: Hot dry wind that blows from the Sahara desert to West Africa. This wind improves the humid and sultry conditions of West Africa significantly.
Mangoshowers: Winds that blow in South India during summer and bring rainfall in Kerala and coastal Karnataka. It acquires the name owing to the fall of ripe mangoes on its arrival.
Kerala Syllabus 10th Standard Social Science Important Questions