Atmospheric Pressure and Winds - Questions & Answers

EXERCISES

I. Choose the correct option:

1. Assertion (A): Variations in pressure cause horizontal movements of air called winds.
Reason (R): Winds transport heat and moisture from one region to another and affect both temperature and humidity.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R does not explain A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer: (b) Both A and R are true but R does not explain A.

2. The decrease in the pressure per unit distance in the direction in which the pressure decreases most rapidly is called
(a) Pressure Gradient
(b) Distance Pressure
(c) Decreased Pressure
(d) Unit/Distance Gradient
Answer: (a) Pressure Gradient

3. What are also called the Horse Latitude?
(a) Equatorial Low Pressure Belts
(b) Sub-Tropical High Pressure Belts
(c) Circum-polar Low Pressure Belts
(d) Polar High Pressure Areas
Answer: (b) Sub-Tropical High Pressure Belts

4. Which pressure belt is also called Doldrums?
(a) Equatorial Low Pressure Belts
(b) Sub-Tropical High Pressure Belts
(c) Circum-polar Low Pressure Belts
(d) Polar High Pressure Areas
Answer: (a) Equatorial Low Pressure Belts

5. Which amongst the following is NOT a characteristic of Trade Winds?
(a) They have varying velocity and are irregular
(b) They are permanent or prevailing winds
(c) They are called North-East Trades in Northern Hemisphere
(d) They have fixed velocity and are regular
Answer: (a) They have varying velocity and are irregular

6. Alps : _________ :: Rockies : _________
(a) Chinook, Mistral
(b) Polar Easterlies, Foehn
(c) Foehn, Mistral
(d) Foehn, Chinook
Answer: (d) Foehn, Chinook

7. What is the tropical cyclone over land called?
(a) Tropical Cyclone
(b) Temperate Cyclone
(c) Tornado
(d) Mistral
Answer: (c) Tornado

8. Study the direction of wind in the picture. The anticyclone is occurring in the _________.
(a) Northern Hemisphere
(b) Southern Hemisphere
(c) Equatorial Region
(d) Polar Region
Answer: (a) Northern Hemisphere

9. The concentrated bands of rapid air movement at the tropopause:
(a) Jet Streams
(b) Tornado
(c) Mistral
(d) Wave Cyclones
Answer: (a) Jet Streams

10. Which of the following is true about Jet streams?
(a) Forecast weather
(b) Reduce flight time
(c) Increase precipitation
(d) All of the above.
Answer: (d) All of the above.

11. Calm region in the centre of the cyclone:
(a) focus
(b) eye
(c) core
(d) All of the above.
Answer: (b) eye

12. Which of the following is NOT a tropical cyclone?
(a) hurricane
(b) typhoons
(c) mistral
(d) willy-willies
Answer: (c) mistral

13. Your uncle was puzzled because his flight from Delhi to London was more than 9½ hours long but his return from London was about 8½ hours. As a student of geography how would you explain this to him?
(a) The pressure gradient supported the return flight.
(b) Flying along a jet stream reduces flight time.
(c) The Coriolis Force deflects air reducing flight time.
(d) None of the above.
Answer: (b) Flying along a jet stream reduces flight time.

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II. Short Answer Questions

1. Name the four main pressure belts of the earth.
Answer: The four main pressure belts are the Equatorial Low Pressure Belt, Sub-tropical High Pressure Belts, Circum-polar Low Pressure Belts, and Polar High Pressure Areas.

2. What is the Circum-polar Low Pressure Belt?
Answer: These are low pressure belts located between 60° and 70° latitudes in both hemispheres. They are formed because the earth's rotation pushes the bulk of the air away from this region towards the Equator, creating a low-pressure zone.

3. How does the Coriolis Force vary latitudinally?
Answer: The deflection caused by the Coriolis Force is the least at the Equator and greatest at the Poles.

4. Name the three chief types of winds.
Answer: The three chief types of winds are Permanent (or Prevailing/Planetary) Winds, Periodic Winds, and Local Winds.

5. What are periodic winds?
Answer: Periodic winds blow at regular intervals or in regular cycles. They result from localised differences in pressure and temperature, such as land and sea breezes and seasonal monsoons.

6. What are local winds? Name any two local winds.
Answer: Local winds are restricted to a certain place only. They blow in comparatively small areas and have special characteristics depending upon the area. Two examples are Loo and Mistral.

7. Name two types of variable winds. Why are they so called?
Answer: Two types of variable winds are Cyclones and Anticyclones. They are called variable winds because they do not blow in any definite direction and their direction varies with the movement of the pressure system.

8. Why are cyclones frequent in summer in the tropical region?
Answer: They are more frequent in summer because of the movement of the Doldrum belt away from the Equator. This leads to intense heating over the warm oceans, triggering the formation of low-pressure centers.

9. Mention any two differences between Tropical Cyclones and Temperate Cyclones.
Answer: 1. Tropical cyclones are produced mainly over the sea, while temperate cyclones are produced both on land and sea. 2. Tropical cyclones are limited to a small area, whereas temperate cyclones occupy areas measuring thousands of kilometres.

10. How are cyclones named differently in different parts of the world?
Answer: Cyclones are known as hurricanes in the Caribbean, typhoons in China and Japan, willy-willies in Australia, and tornadoes over land in North America.

11. What are two chief characteristics of anticyclones?
Answer: 1. They are centers of High Pressure surrounded by Low Pressure. 2. Winds blow gently outwards, moving clockwise in the Northern Hemisphere and anti-clockwise in the Southern Hemisphere, bringing fine and clear atmospheric conditions.

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III. Define the following terms:

(a) Pressure Gradient.
Answer: The decrease in pressure per unit distance in the direction in which the pressure decreases most rapidly.

(b) Winds.
Answer: Horizontal movement of the air from high pressure areas to low pressure areas is called wind.

(c) Coriolis force.
Answer: A force produced by the earth's rotation on its axis that deflects the actual direction of winds from a straight path.

(d) Altitude.
Answer: The height of a place above sea level. Atmospheric pressure and temperature both decrease with an increase in altitude.

(e) Monsoons.
Answer: Periodic seasonal winds primarily blowing in South East Asia and Northern Australia, developing due to differences in the heating conditions of continents and oceans.

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IV. Distinguish between the following:

1. Cyclones and Anticyclones.
Answer: A cyclone is an intense low-pressure depression with winds blowing inward, causing violent weather, strong winds, and heavy rainfall. An anticyclone is a high-pressure center with gentle winds blowing outward, associated with fine, clear, and calm weather.

2. Permanent and Periodic Winds.
Answer: Permanent winds blow throughout the year in a steady direction across latitudes in response to global pressure belts (e.g., Trade Winds). Periodic winds reverse their direction periodically with the season or time of day due to localized temperature and pressure differences (e.g., Monsoons).

3. Summer and Winter Monsoons.
Answer: Summer monsoons blow from the sea to the land (e.g., South-West Monsoon in India) and bring heavy rainfall. Winter monsoons blow from land to sea (e.g., North-East Winter Monsoon) bringing cold, dry weather and generally do not produce rain unless they cross oceans.

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V. Structured Questions

1. (a) What is meant by the term 'Atmospheric Pressure'?
Answer: Atmospheric Pressure refers to the force per unit area exerted against a surface by the weight of the air above that surface.

(b) Explain briefly the factors that affect Atmospheric Pressure.
Answer: The main factors are: 1. Altitude (pressure decreases as height increases because air becomes less dense), 2. Temperature (warm air expands and exerts less pressure, cold air contracts and exerts more), 3. Water Vapour (humid air is lighter than dry air, lowering pressure), and 4. Rotation of the earth (centrifugal forces push air from poles to equator, affecting pressure distribution).

(c) Give a geographical reason for each of the following:
(i) The Westerlies in the Southern Hemisphere blow with greater force than those in the Northern Hemisphere.
Answer: This is due to the absence of huge landmasses in the Southern Hemisphere, which allows the oceanic Westerlies to gather strength and blow forcefully without obstruction.

(ii) There is a seasonal shifting in pressure belts.
Answer: The earth is inclined 23½° towards the sun. Due to this inclination, the sun shines vertically over the Tropics at different times of the year, causing the pressure belts to shift 5° northwards in the Northern summer and 5° southwards in the Northern winter.

(iii) As we go higher, the atmospheric pressure decreases.
Answer: As altitude increases, the overlying layers of air are thinner, less dense, and have fewer gas molecules due to reduced pull of the earth's gravity, which lowers the air pressure.

(d) Draw a well labelled diagram showing the pressure and wind belts of the earth.
Answer: [Students are expected to draw a diagram mapping the Equatorial Low, Sub-tropical Highs, Circum-polar Lows, and Polar Highs, along with the directions of Trade Winds, Westerlies, and Polar Easterlies.]

2. (a) Briefly explain the three chief types of winds.
Answer: The three chief types are: 1. Permanent Winds that blow constantly throughout the year (Trade Winds, Westerlies, Polar Easterlies). 2. Periodic Winds that blow at regular intervals or reverse seasonally (Monsoons, Land/Sea Breezes). 3. Local Winds that are restricted to small specific geographic areas (Loo, Chinook).

(b) Describe some of the important types of local winds.
Answer: Some important local winds are Loo (a hot, dry summer wind in northern India), Foehn (a warm, dry wind descending the Alps), Chinook (a warm, dry "snow eater" descending the Rockies), and Mistral (a bitterly cold wind blowing down from the Alps over France).

(c) Give a geographical reason for each of the following:
(i) The winds are directed to the right of their flow in the Northern Hemisphere.
Answer: This deflection is caused by the Coriolis Effect, a force generated by the rotation of the earth on its inclined axis.

(ii) Temperature and pressure are inversely related to one another.
Answer: When temperature increases, air gets heated, expands, becomes less dense, and thus exerts less pressure. Conversely, cold air compresses, becomes dense, and exerts higher pressure.

(iii) Humid air is lighter than dry air.
Answer: The molecular weight of water vapour is less than the average molecular weight of dry air. Thus, when water vapour mixes in the air, a volume of humid air weighs less than an equal volume of dry air.

(d) What is Coriolis Effect? How does it affect the planetary winds?
Answer: The Coriolis Effect is a force caused by the earth's rotation that deflects moving air. It prevents planetary winds from moving in a straight line, deflecting them to their right in the Northern Hemisphere and to their left in the Southern Hemisphere.

3. (a) Explain the weather conditions associated with tropical and temperate cyclones.
Answer: Tropical cyclones are associated with violent winds of great speed, dense clouds, and heavy rain, while the center (eye) remains perfectly calm. Temperate cyclones approach with a fall in temperature, shifts in wind, and a halo around the sun/moon, followed by a light drizzle that turns into a heavy downpour continuing for many days.

(b) What are the Jet Streams? What is the significance of the Jet Streams?
Answer: Jet streams are concentrated bands of rapid air movement found at the tropopause. They are significant because they steer global weather systems, helping meteorologists forecast weather events, and are utilized by commercial airlines to significantly reduce flight times and fuel consumption.

(c) Give a geographical reason for each of the following:
(i) Doldrums is a low pressure belt.
Answer: The intense heating from the vertical rays of the sun at the equator causes the air to constantly expand and rise as convection currents, resulting in a low pressure zone of total calm.

(ii) Equatorial regions have low atmospheric pressure throughout the year.
Answer: The equatorial region receives a great amount of direct heat from the sun throughout the year, meaning the air is perpetually warm, light, and rising.

(iii) Low atmospheric pressure prevails over the Circum-polar region.
Answer: The rotation of the earth generates centrifugal forces that push the bulk of the air at these latitudes (60° to 70°) outward towards the Equator, causing a low pressure belt to form.

(d) Draw a well labelled diagram showing a cyclone in the Northern Hemisphere.
Answer: [Students are expected to sketch a low-pressure core surrounded by high-pressure isobars, with inward-blowing winds deflecting to form an anti-clockwise spiral.]

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VI. Thinking Skills

1. State two situations when you physically felt the effect of the atmospheric pressure. Give reasons to support your answer.
Answer: 1. Feeling breathless while traveling in high mountains, because high altitudes have lower atmospheric pressure and thinner air with less available oxygen. 2. Experiencing a "popping" sensation in the ears while on a flight or quickly driving up a hill, which occurs as the body adjusts to the rapid drop in outside atmospheric pressure.

2. You must have read in newspapers or seen on TV channels, the news of cyclonic storms like Amphan, Nisarga, Fani, Yaas, Tauktae, Gulab, etc. affecting different parts of the country. Find out the origin and effects of at least three of these cyclonic storms.
Answer: 1. Amphan (2020) originated in the Bay of Bengal and caused violent winds and severe infrastructural damage in West Bengal and Odisha. 2. Tauktae (2021) originated in the Arabian Sea and brought heavy rainfall and extensive destruction along the western coast of India, notably Gujarat and Maharashtra. 3. Fani (2019) developed in the Bay of Bengal and struck the Odisha coast as an extremely severe cyclonic storm, causing massive power outages and property damage.

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VII. Project Work

In 2019, the Arabian Sea recorded the formation of four cyclones, Vayu, Hikka, Kyarr and Maha — a phenomenon after more than a century. Formation of cyclonic storms is normal in the Arabian Sea but rare if it develops in October-November. Usually the Bay of Bengal sees cyclones during this period. Prepare a project report tracing cyclonic storms that occurred along the eastern coast as well as the western coast of India over last ten years.
Answer: [This is a practical assignment. Students will gather data and compile a report listing the major tropical cyclones over the last ten years, marking their origin (Bay of Bengal vs. Arabian Sea), plotting their storm tracks on a map of India, and summarizing their impacts on life and property along the affected coastal states.]