WBBSE Chapter 2 Atmosphere Short Question And Answers

Question 1. What may happen due to the creation of the ozone hole?
Answer:

• Importance of the ozone layer: The ozone layer protects the earth like an umbrella from the harmful ultraviolet rays of the sun. It saves plant and animal life from decay and diseases.
• The consequence of the ozone hole: The creation of an ozone hole will allow the harmful ultraviolet rays of the sun to enter the earth’s atmosphere. This will cause several diseases like skin cancer, damage of the cornea of the eyes, infertility, skin diseases, death of fishes and other aquatic life, wilting of leaves of plants, etc.

Question 2. Write the effects of depletion of the ozone layer.
Answer:

The effects of depletion of the ozone layer:

The ozone layer is being gradually depleted by CFCs, nitrogen oxide, sulfate compounds, etc.

The effects of ozone layer depletion are—

• On climate: The depletion of the ozone layer allows the harmful ultraviolet rays of the sun to enter the earth’s atmosphere. This causes global warming, which further leads to the depletion of the ozone layer.
• On human beings: The depletion of the ozone layer causes skin cancer and other skin diseases, reduces fertility, damages the cornea of the eyes, etc.
• On ecosystem: The ecosystem is also hampered due to ozone layer depletion. Plants lose productive capacities. Many small animals may get extinct.

Question 3. Why do jet planes fly through the stratosphere?
Answer:

• The jet planes fly through the stratosphere because—
  
  The stratosphere is free of water vapor and weather phenomena like winds, thunderstorms, rainfall, etc. The very fine dust particles present here do not hamper the flying of planes.
• This layer is practically devoid of air and there is very little friction and no disturbances in the atmosphere.
• The presence of jet streams in the tropopause also helps in saving costly aviation fuel because jet streams propel jet planes to fly easily following them.

Question 4. How is the ozone layer contracting?
Answer:

The ozone layer contracting:

• The excessive emission of chlorofluorocarbons, nitrogen oxide, sulfur dioxide, and other greenhouse gases is harming the ozone layer. Big holes have been detected in this layer especially, over the Antarctic region.
• According to scientists, the creation of ozone holes may lead to diseases such as skin cancer, damage to the cornea of the eyes, etc. due to the ultraviolet rays reaching the earth’s surface

Question 5. Why are days very hot and nights very
Answer:

The days are very hot and the nights are very cold in hot desert regions because—

• The clear sky in hot desert regions allows solar radiation to reach the earth’s surface and heat it up fast. Thus, sands present in the desert regions get heated up fast and accordingly heat up the atmosphere. Thus, the temperature rises very high during the daytime.
• After the sun sets, the sands of the deserts radiate back heat very fast. Due to the clear sky, the heat is released into space very fast and the sand cools down. This makes the nights cold in the hot desert regions.

Question 6. Why are cloudless nights cooler than cloudy nights?
Answer:

• The cloud cover of the sky prevents the insolation to reach the earth’s surface during the daytime and terrestrial radiation of the solar energy into space in the afternoon. This makes the days comparatively cooler and the nights comparatively warmer in cloudy conditions.
• On the other hand, if the sky is clear and cloudless, the insolation heats up the atmosphere very much during the daytime and the energy is fully radiated back during the night. Thus, the days seem to be warmer and the nights seem to be cooler.

Question 7. Mention the factors that influence the heat budget of the earth.
Answer:

The amount of solar energy received by the earth, or the heat budget of the earth is maintained by the following factors—

1. Angle of incidence of sun’s rays: The lower latitudes receive perpendicular rays of the sun and the rays become inclined as the latitudes increase. Thus, the equatorial region and lower latitudes receive more heat than the higher latitudes and polar regions.

2. Distance between the earth and the sun: The earth moves around the sun in an elliptical orbit. Hence, sometimes the distance between the sun and the earth decreases and sometimes increases. This affects the amount of heat received by the earth’s surface.

3. Length of day and night: The regions which have longer daytime receive more solar energy than the regions which have longer nights.

Question 8. Mention the different methods of calculating and recording the temperature of a place.
Answer:

The different methods of calculating and recording the temperature of a place

Temperature is recorded by the thermometer. Generally, the Six’s maximum and the minimum thermometer are used to record the maximum and minimum temperatures of the day of a particular place.

This is also used to calculate the—

1. Average daily temperature = Highest temperature of the day + Lowest temperature of the day.
2. Average annual temperature = Total of the monthly average temperatures
3. Range of temperature = Highest temperature – The lowest temperature

Question 9. Why does Mt. Kilimanjaro remain snow-covered even though it is located on the equator? OR, Why does the capital of Ecuador, Quito have a subtropical highland climate?
Answer:

Mt. Kilimanjaro is located on the equator and is 5.9 km in altitude. The average temperature of the equatorial region is 27°C. By the lapse rate, the average temperature of the peak of Mt. Kilimanjaro is 27°C – (6.4°C x 5.9) = -10.76°C. Thus, Mt. Kilimanjaro remains snow-covered throughout the year.

• The capital of Ecuador, Quito is located in the equatorial region at 2.8 km above mean sea level. The average temperature of the equatorial region is 27°C.
• Thus, by the lapse rate, the average temperature of Quito is 27°C – (6.4°C x 2.8) = 9.08°C. Thus, Quito enjoys a sub-tropical highland climate.

Question 10. Why does the water of the Baltic Sea freeze but water around the British Isles does not freeze in spite of both lying along the same latitude?
Answer:

• The latitude at which the British Isles as well as the Baltic Sea lies, makes the region very cold. Thus, it is very natural for water to freeze.
• But the warm Gulf Stream passing along the coast of the British Isles keeps the water warm and prevents it from freezing during winter.
• On the other hand, the Baltic Sea is surrounded by land, and no warm current flows through it. Thus, the water becomes very cold and freezes during winter.

Question 11.  Why do landmasses get heated faster than water bodies?
Answer:

Landmasses get heated faster than water bodies because of the following reasons—

1. The heat received by water bodies is transferred to the depths by the convectional currents. No such convectional currents work on landmasses.
2. The absorption of solar energy is lower over water bodies than landmasses. Thus, landmasses get heated quicker than water bodies.
3. The amount of energy required to heat up per unit volume of water by 1°C is about three times the energy required to heat up per unit volume of landmasses by 1°C. Thus, if the same amount of energy is supplied, landmasses get heated faster than water bodies.
4. Water being transparent, solar energy penetrates up to 200m depth and distributes the heat. Land being opaque, heat gets concentrated on the surface only.

Question 12.  Discuss the causes of global warming.
Answer:

The major causes of global warming are—

1. Excessive use of fossil fuels: The excessive use of fossil fuels in vehicles, industries, and thermal power plants is increasing the level of carbon dioxide in the atmosphere. The gas absorbs much heat and Increases the temperature of the earth.

2. Emission of methane gas: Methane is a greenhouse gas emitted from wetlands, waterlogged rice fields, decaying organic matter, excreta of domestic animals, etc. This plays an important role in increasing the temperature of the earth.

3. Deforestation: Reckless cutting down of trees leads to deforestation. This is gradually increasing the percentage of carbon dioxide in the atmosphere, which is a greenhouse gas. The concentration of carbon dioxide in the atmosphere is increasing the earth’s temperature and causing global warming.

4. Emission of nitrous oxide: The use of nitrogen-rich fertilizers in agriculture, forest fires, etc. emits a huge quantity of nitrous oxide (N20), which leads to global warming.

5. CFC gases: The use of refrigerators, air; conditioners, electronic gadgets, body sprays, cosmetics, etc. increase the use of chlorofluorocarbons (CFCs) which is one of the major causes of global warming.

Question 13. What is El Nino? Discuss its influences.
Answer:

El Nino:

El Nino is a southward-moving warm current of the Pacific Ocean which flows along the western coasts of Peru and Ecuador. El Nino causes a considerable rise in the air temperature of the eastern Pacific Ocean.

Influences or effects:

1. El Nino causes heavy rainfall in the coastal areas of Peru and Ecuador that often leads to flooding.
2. Dry weather persists in the Amazon basin, Central America and Australia. This often causes forest fires.
3. According to climatologists, El Nino also influences the circulation of the monsoon winds. Hence, in the years when El Nino Occurs, India experiences droughts, The desert regions of Chile and Peru experience floods.
4. The warm effect of El Nino kills the coral polyps and other marine creatures.
5. El Nino results in a rise in general temperature and a decrease in rainfall in southeast Asia.

Question 14. What is La Nina? Discuss its influence.
Answer:

La Nina:

The opposite condition of El Nino is known as La Nina. During this time, the surface temperature of the Pacific Ocean in the coastal areas of Peru and Ecuador decreases by 49C or more.

Influence or effects:

1. La Nina causes heavy rainfall along the western coast of the Pacific Ocean.
2. The western coast of South America experiences droughts.
3. Dry weather persists in the USA.
4. Canada experiences chilling cold and heavy snowfall.

Question 15. Why does the atmosphere get heated?
Answer:

The chief source of heat in the atmosphere is the sun. Solar energy reaches the earth’s surface and heats it up. This heat is transmitted into the atmosphere by the processes of conduction, convection, and radiation. Apart from this, the absorption of the ultraviolet rays by the ozone layer in the Stratosphere also heats up the atmosphere considerably.

Question 16. Discuss the characteristics of air temperature as found in different regions of the earth.
Answer:

The characteristics of air temperature in different parts of the earth are as follows—

1. Air is warmest at the equator and coldest at the poles in both the northern and southern hemispheres.
2. The temperature in the equatorial region remains almost the same throughout the year.
3. Although the polar regions remain very cold throughout the year, differences in air temperature between summer and winter can be seen.
4. The revolution of the earth around the sun results in the highest temperature in the northern hemisphere in July and that in the southern hemisphere in January. Reverse conditions are found during winter.
5. Temperature decreases by 6.4°C for every 1000 m rise in altitude. This is known as the normal lapse rate.
6. Winds are warmer along coasts where warm ocean currents flow, and cooler along coasts where cold ocean currents flow.
7. If a warm wind blows over an area, the temperature increases and vice versa.

Question 17. How is air temperature measured?
Answer:

Air temperature measured:

Air temperature is measured by the thermometer in degrees Celsius (°C) and degrees Fahrenheit (°F). The Six’s maximum and the minimum thermometer are used to measure the maximum and minimum temperature of a day. This is used to calculate the diurnal range of temperature, monthly average temperature, monthly range of temperature, and annual range of temperature.

Question 18. What are the ‘thermal zones’ of the earth? Name the different thermal zones on earth.
Answer:

The earth can be divided into different circular belts or zones according to the level of temperature persisting in different parts of the earth. These zones are known as thermal zones of the earth.

Thermal zones: There are five thermal zones on the earth’s surface—

1. Torrid zone — (231/iN- 2334°S),
2. North Temperate zone — (23y2N -661/2°N),
3. South Temperate zone — (2334S -66/4°S),
4. North Frigid zone — (661/2°N-90°N),
5. South Frigid zone — (66/4°S-90°S)

Question 19. Discuss The Causes Of the Formation Of The Torrid Zone.
Answer: 

Location: The region lying between 231/2°N and 231/2°S latitudes across the equator is known as the Torrid zone.

Causes: The angle of incidence of sun’s rays varies between 43° and 90° in this region. Thus, the heat received here is maximum. The sun’s rays traverse a smaller distance in the atmosphere before reaching the earth’s surface. Thus, the loss of heat due to scattering, absorption, and reflection is less. The Torrid zone remains warm throughout the year, and the average temperature is around 27°C.

Question 20. What is the diurnal range of temperature of a place with a maximum temperature of 38°C and a minimum of 26°C?
Answer:

Diurnal Range of temperature = Maximum temperature – Minimum temperature = 38°C- 26°C = 12°C
Therefore, the diurnal range of temperature of the place is 12°C.

Question 21. Calculate the average temperature of Suri if the maximum temperature was 35X and the minimum was 2SX on 12th April 2018.
Answer:

Average temperature Maximum temperature + Minimum temperature/2
=35 +28/2 = 63/2
=31.5

Question 22. Calculate the average annual temperature of Maldah from the following table.

1. 

2. 

Answer: = Average annual temperature total of average monthly /12 = 2888.10/12 =24.01c

Question 23. Why are winter nights colder in Delhi than in Mumbai?
Answer:

The winter nights are colder in Delhi than in Mumbai because of the following reasons—

1. Mumbai is located on the coast of the Arabian Sea. Thus, it enjoys a moderate or maritime climate. Delhi is located far away from the influence of the sea. Thus, it experiences extreme or continental climates.

2. Mumbai is located at 19°04′ N latitude and Delhi is located at 28°42′ N latitude.

• Thus, Delhi is located comparatively northward of Mumbai. The angle of incidence of sun’s rays is slightly more inclined in Delhi than in Mumbai.
• Hence, Mumbai receives more heat than Delhi. During the night, the lesser amount of heat absorbed by Delhi is radiated back faster than that by Mumbai. Thus, nights are warmer in Mumbai than in Delhi.

Question 24. Why is London cooler than Kolkata?
Answer:

London is cooler than Kolkata for the following reasons—

• Kolkata is situated at 22°30′ N latitude and London is situated at 51°30′ N latitude. London because of its location far north of Kolkata receives the sun’s rays at a more inclined angle than Kolkata.
• Hence, the average temperature in London is lower than that of Kolkata. Thus, London is cooler than Kolkata.

Question 25.Why are places in higher altitudes cooler than that in lower altitudes?
Answer:

The causes of places at higher altitudes being cooler are as follows—

1. The amount of water vapor and dust particles in the air decreases with an increase in altitude. Thus, absorption and retention of heat are less.
2. The density of air in higher altitudes is less. The light winds radiate heat quickly and become cool.
3. Effects of conduction, convection, and radiation of heat in higher altitudes are quite less. The temperature remains low due to the normal lapse rate.

Question 26. Mention the main characteristics of the range of temperature.
Answer:

The main characteristics of the range of temperature are—

1. The range of temperature throughout the day, month, or year is lowest at the equator.
2. The range of temperature is highest in higher latitudes.
3. The range of temperature is greater over landmass than on water bodies.

Question 27. What do you mean by ‘Normal Lapse
Answer:

Normal Lapse:

• The earth’s surface gets heated first by the insolation.
• This energy is then transmitted to the atmosphere by the processes of conduction, convection, and radiation.
• Generally, temperature decreases by 6.4°C for every 1000 m or 1 km rise in altitude. This rate of decrease in temperature is known as the normal lapse rate.
• The higher altitudes remain cooler and the high mountains remain snow-capped due to the lapse rate of temperature.

Question 28. Explain the process of transfer of heat by conduction.
Answer:

The process of transfer of heat by conduction:

• Conduction is the mode of heat transfer from one part of a substance to another part within the substance itself or to a different substance that is placed in physical contact. In conduction, there is no noticeable movement of molecules.
• Energy is transferred by the movements of free electrons through vibrations between atoms and molecules.

Example: ln the atmosphere, the lower layers transfer heat to the upper layers by the method of conduction. This occurs best during the daytime.

Question 29. Explain the process of convection in the transfer of heat.
Answer:

The process of convection in the transfer of heat:

The air adjacent to the earth’s surface especially in the equatorial region gets most heated, becomes light and rises. Air from adjacent areas which is cooler and heavier rushes to fill up this vacuum created. This cyclical movement of warm air upward and cooler air downwards and sidewards to fill up the gap is known as convection.

The atmosphere gradually gets heated from below upwards by the physical movement of gas molecules from bottom to top. Convection is mostly seen in the equatorial region due to vertical rays of the sun falling on this region

Question 30. Name the factors responsible for differences in temperature in different parts of the earth.
Answer:

The main factors responsible for differences in temperature in different parts of the earth are—

1. Latitude,
2. Altitude,
3. Length of day and night,
4. Presence of mountains,
5. The slope of the land and
6. Distance from the sea.

Question 31. What do you mean by the greenhouse effect?
Answer:

Greenhouse effect:

The gradual increase of the earth’s temperature due to the presence of certain gases in the atmosphere is known as the greenhouse effect.

The carbon dioxide, methane, and chlorofluorocarbons present in the atmosphere create a transparent envelope in the atmosphere which prevents solar energy from radiating back to space. Thus, the temperature of the earth’s atmosphere gradually increases.

Question 32. Name some greenhouse gases.
Answer:

Some greenhouse gases present in the atmosphere are—

1. Carbon dioxide,
2. Methane,
3. Chlorofluorocarbons,
4. Carbon monoxide,
5. Nitrous oxide,
6. Water vapor, etc. Amongst these, carbon dioxide is the most important greenhouse gas.

Question 33. How does the difference in air pressure generate winds?
Answer:

• Winds are generated primarily due to differences in pressure conditions between two regions. If the ground gets heated too much, the adjacent air also gets heated. This air becomes lighter and tends to rise upward.
• Thus, a vacuum or low-pressure cell is created. Winds from the adjacent cooler regions rush towards this low-pressure region and try to bring a balance in the pressure conditions.
• Thus, winds blow from high-pressure regions to low-pressure regions.

Question 34. List the characteristics of tropical cyclones.
Answer:

The characteristics of tropical cyclones are—

1. The center of the cyclone, where the pressure remains the lowest is called the eye of the cyclone.
2. Generally, clear skies and calm conditions prevail in the eye region of the cyclone.
3. The eye of the cyclone is surrounded by cumulonimbus clouds.
4. Winds rush in from the region around the eye with great speed and cause thunderstorms and rainfall.
5. The cyclones move in an anticlockwise direction in the northern hemisphere and a clockwise direction in the southern hemisphere.

Question 35. Write a short ‘north westers’.
Answer:

‘North westers’

• North ‘westers or Kalbaishakhi is a tropical storm that occurs in India and Bangladesh. In India, the states of West Bengal, Odisha, Bihar, Jharkhand, and Assam come under the influence of northwestern in the summer season.
• This is a sudden wind that causes thunderstorms, rainfall, and sometimes hailstorms.

North westers Causes:

• During the summer season, the day-long heating of the Chotanagpur plateau heats up the adjacent air.
• Thus, warm air rises upwards and creates a low-pressure cell over the rocky plateau region.
• This low-pressure cell is the main cause of drawing winds from the surroundings and forming a tropical storm.
• Usually, the air comes from the north-western direction to fill up the low-pressure region, hence the name ‘northwestern’ (north + western).

North westers Effects:

• The day’s temperature may fall up to 10° C with little rainfall.
• However, rainfall is beneficial for tea, rice, and jute cultivation.

Question 36. What are the causes of planetary winds?
Answer:

The causes of planetary winds

• The general characteristic feature of wind is that it blows from the high-pressure region to the low-pressure region. There are seven fixed pressure belts found on the earth’s surface.
• These high-pressure and low-pressure belts lie and alternate with each other from the equator to the poles.
• As these pressure belts are fixed, certain fixed winds blow between the two adjacent high-pressure and low-pressure belts. These winds are called planetary winds.
• Planetary winds such as Trades, Westerlies, and Polar winds blow from sub-tropical high-pressure belts to equatorial and polar low-pressure belts over the earth’s surface throughout the year in fixed directions.

Question 37.  Why do the westerly winds blow with more speed in the southern hemisphere than in the northern hemisphere?
Answer:

The westerly winds blow between 35°and 60° latitudes in both the hemispheres.

• The presence of huge landmasses in the northern hemisphere reduces the speed of the winds blowing over them due to friction.
• But in the southern hemisphere, there are more water bodies or oceans than land.
• Hence, the degree of friction is very less, and winds can blow uninterruptedly with great speed over oceans.
• The speed of westerlies in the southern hemisphere is so great that they make roaring, screeching, and shrieking noises as they blow. 

Question 38. Discuss the role of the trade winds in the creation of deserts.
Answer:

The role of the trade winds in the creation of deserts

• The trade winds blow from the subtropical regions to the equatorial regions, i.e, from higher latitudes towards lower latitudes.
• As they blow from comparatively cooler regions to warmer regions, the wind gets warmer.
• The moisture-holding capacity of the wind increases and hence chances of rainfall is reduced.
• Thus, dry weather persists in the regions over which trade winds blow. The hot deserts of Sahara, Thar, Kalahari, Atacama, etc. lie in the path of trade winds.

Question 39. What are local winds? Give examples.
Answer:

Local winds

The winds that blow due to the influence of local geographical features and environmental conditions are called local winds.

Some of the local winds are-

Loo: This is a hot dry wind that blows over north-western India during the daytime.
Foehn: This is a warm dry wind that blows over the northern slopes of the Alps mountains in Europe through the Rhine river valley.

Question 40. What is loo’? When does this wind blow? Where in India is Loo found to blow?
Answer:

Loo

‘Loo’ is a strong, dusty, hot, dry wind. It blows during the summer season (very strong in April-May) in India.

Area: The Loo blows over the Indo-Gangetic Plain region of North India. Rajasthan, Uttar Pradesh, Delhi, and Madhya Pradesh mainly come under its influence.

Question 41. Explain the causes of winds.
Answer:

Causes of winds

• Winds blow from high-pressure regions to low-pressure regions. If the temperature of a place increases, the air becomes warm and tends to rise as it becomes light.
• Thus, a low pressure is created. Cooler winds from adjacent areas rush towards this low-pressure region to fill up the gap. Thus, the main cause of winds is a difference in air pressure.

Question 42. What do you mean by air pressure?
Answer:

Air pressure

Air pressure is an important element of weather and climate. Air has mass, and like any other material having mass, it is attracted by gravity.

Thus, the weight that a unit volume of air exerts on the earth’s surface is known as air pressure. Under normal conditions, air pressure is 1 kg per square centimeter.

Question 43. What are isobars?
Answer:

Isobars

• Isobars are imaginary lines drawn on weather maps joining places having the same pressure conditions.
• The air pressure decreases by 34 millibars with a 300 m rise in height above sea level.
• Thus, before drawing the isobars, the pressure conditions of the places concerned must be converted to pressure conditions at sea level height.

Question 44. Why do mountaineers use oxygen cylinders in high altitudes in the Himalayan region?
Answer:

• Air pressure remains high near the earth’s surface or the mean sea level and goes on the same decreasing with an increase in altitude as the air becomes thinner with the rise in altitude.
• The density of air decreases with decreasing air pressure. The amount of oxygen left in the upper air is not sufficient for normal breathing.
• Hence, mountaineers use oxygen cylinders when they go to higher altitudes or for climbing peaks

Question 45. Why have hot deserts been formed in the path of the trade winds?
Answer: The trade winds blow from the subtropical regions to the equatorial regions, i.e, from higher latitudes towards lower latitudes. As they blow from comparatively cooler regions to warmer regions, the wind gets warmer.

The wind’s moisture-holding capacity increases, reducing the chances of rainfall. Thus, dry weather persists in the regions over which trade winds blow. The hot deserts of the Sahara, Thar, Kalahari, Atacama, etc. lie in the path of trade winds.

Question 46. Why don’t we feel the pressure exerted by the earth’s atmosphere on us?
Answer:

• Air pressure is 76 cm of mercury column which is about 10,360 kg per square meter.
• The atmospheric pressure of the air around us is almost the same or similar to the pressure exerted by blood in our bodies.
• Thus, there is a balance between atmospheric pressure and body pressure.
• Hence, we do not feel the atmospheric pressure exerted by the column of air in the atmosphere around us.

Question 47. Why does air pressure decrease with an increase in altitude?
Answer:

The air pressure decreases with an increase in altitude because of the following reasons—

1. The density of air decreases with an increase in altitude. Air becomes thin, and light, and hence pressure decrease.
2. The number of air molecules or gaseous molecules present in higher altitudes is lesser than that present at lower altitudes.
3. Air pressure decreases by 1 cm of mercury column with every 110 cm rise in altitude. If the air pressure at sea level is considered 100%, it becomes about 1% at an altitude of 18 km.

Question 48. What is the unit for measuring air W pressure?
Answer:

The unit of ‘millibar’ is used to measure air pressure.

1 millibar is equivalent to 1000 dyne per sq. cm. Dyne is the unit of measuring force.
1 dyne is almost equal to 1 kg. Air pressure is measured with the help of a barometer. The mercury column in the barometer indicates the pressure conditions of the surrounding area.

Question 49. What is a jet stream?
Answer:

Jet stream

The thin stream of air blowing through the I upper atmosphere from the west to the east
at a very high speed (110-500 km/hr) is known as the jet stream. The tropical and sub-tropical jet streams influence the climate of India.

Question 50. What are trade winds?
Answer:

Trade winds

The planetary winds that blow from the subtropical high-pressure zones in the northern and southern hemispheres towards the equatorial low-pressure zone in a particular direction throughout the year, are called trade winds.

They are basically easterly winds, i.e., they blow from the northeast to the southwest in the northern hemisphere and from the southeast to the northwest in the southern hemisphere. In the early days, these winds helped in trading across the oceans by sailing ships. Hence, they are called the trade winds.

Question 51. What are anti-trade winds
Answer:

Anti-trade winds

The planetary winds that blow in the opposite direction of trade winds are called anti-trade winds. In both the northern and southern hemispheres, the winds blow towards the sub-polar low-pressure zone near the Arctic and Antarctic circles from the high-pressure zone near the tropics.

The direction of the wind in the northern hemisphere is from southwest to northeast, and that in the southern hemisphere is from northwest to southeast. Thus, these winds are also known as westerly winds

Question 52. Why are the westerlies more speedy in the southern hemisphere?
Answer:

• The amount of landmass is greater in the northern hemisphere than in the southern hemisphere. Thus wind gets obstructed in the northern hemisphere by the land and slows down due to friction.
• On the other hand, winds blow unhindered in the southern hemisphere over the oceans. Thus, wind speed is greater in the southern hemisphere than in the northern hemisphere.

Question 53. What are roaring forties?
Answer:

Roaring forties

In the southern hemisphere, the presence of landmarks is very less beyond the 40JS latitude. Thus, the westerly winds blow with extreme speed over the oceans due to very less friction with the water. These winds make much noise while blowing. Hence, the latitude adjacent to the 40°S latitude is referred to as the roaring forties.

Question 54. What are planetary winds?
Answer:

Planetary winds

The winds that blow over the earth throughout the year from a fixed direction without much fluctuation, are called planetary winds. They can be classified into three types-

1. Trade winds,
2. Westerlies and
3. Polar winds.
4. The planetary winds develop due to the rotation of the earth and the existence of the pressure belts around the earth.

Question 55. What do you mean by monsoon winds?
Answer:

Monsoon winds

Monsoon winds are periodic winds generated in certain places due to differences in temperature and pressure conditions on land and water in different seasons of the year. Monsoon winds blow from opposite directions in different seasons of the year.

If the southwest monsoon blows over the Indian subcontinent from the southwest direction during summer. It blows from the reverse direction as the northeast monsoon wind during winter.

Question 56. What is a cyclone?
Answer:

Cyclone

• A cyclone is a sudden wind developed due to a sudden difference in pressure conditions in a region.
• If a low-pressure cell is created at any point due to excessive heating, winds from the adjacent high-pressure regions gush toward the low-pressure cell in circular motions with great speed.
• Cyclones can be highly devastating and may last from a few hours to a few days. They may cause heavy rainfall if they are generated near coastal areas.

Cyclones can be classified into two types—

1. Tropical cyclones and
2. Temperate cyclones.

Question 57. What do you mean by the eye of a cyclone?
Answer:

Eye of a cyclone

• The low-pressure cell at the center of a tropical cyclone is known as the eye of the cyclone. It can extend from 20-40 km in diameter.
• The weather conditions in the eye remain calm and cloudless even though severe storms and rainfall may occur in other parts of the cyclone.

Question 58. What is’Chinook7?
Answer:

‘Chinook7

• The ‘Chinook7 is a local wind blowing from the eastern slopes of the Rocky Mountains in North America towards the Prairie region at the foothills of the mountains.
• These are hot and dry winds that cause the snow of the Prairie region to melt. The word ‘Chinook7 means ‘snow eater.
• As this wind melts all the show, it has been so named. The snow melt water moistens the soil of the Prairie region and helps in the growth of vast grasslands.

Question 59. What is ‘Foehn7?
Answer:

Foehn7

‘Foehn7 is a local wind blowing from the Alps mountainous region towards the Rhine valley in Europe.

Effects: The hot and dry wind rises along the slope of the Alps mountains and starts cooling down. The water vapor present in the air condenses and causes rainfall and snowfall.

As the wind crosses the Alps mountains and moves down-slope towards the Rhine valley, it starts expanding. Thus, it becomes warm and dry.

Question 60. What is Sirocco?
Answer:

Sirocco

The hot, dry, dusty wind blowing locally over the Sahara desert is called Sirocco

Effects: The hot dry wind becomes humid as it moves towards the northeast and crosses the Mediterranean sea.
The Sirocco is harmful to the cultivation of olives in Italy and Sicily.

Question 61. What is a loop?
Answer:

Loo

The hot dry local wind blowing in northwestern India is called ‘Loo’. During summer, the land surface in north-western India gets extremely heated.

The air adjacent to this land also gets heated by radiation of this heat. During the afternoon, this heated air blows as very speedy wind parallel to the earth’s surface. The local people call this hot wind ‘Loo’.

Question 62. What is ‘Aandhi’?
Answer:

‘Aandhi’

The Aandhi is a violent, squally dust storm occurring in the summer season in northwestern states of India over Uttar Pradesh, Rajasthan, and Punjab. The wind blows at a very high speed, about 70-100 km per hour.

Question 63. The dust particles blown up by the wind reduce visibility to almost zero and makes
Answer: The surroundings are dark. Hence, it is named ‘Aandhi’ meaning darkness.

Effects: These dust storms may cause very little rainfall. Aandhi helps to reduce the air temperature and the weather feels pleasant after the storms stop blowing.

Question 64. What is a hurricane?
Answer:

Hurricane

The strong tropical cyclone that develops over the Caribbean sea and the islands of the West Indies is called a hurricane. The hurricane may have a diameter of 650 km and blow at an average speed of more than 140 km/hr.

The eye of the hurricane consists of a very deep low-pressure cell.

Question 65. What is a tornado?
Answer:

A violently rotating column of air extending from the base of a thunderstorm to the ground is called a tornado. Tornadoes are often associated with funnel-shaped clouds. In the USA, tornadoes are also known as twisters.

Characteristics:

1. The speed of these storms may reach up to 500 km/hr.
2. The center of the tornado maybe 100-500 m in diameter.
3. A number of tornadoes generated close to each other over a region are considered as the tornado family.

Question 66. What is Mistral wind?
Answer:

Mistral wind

The strong, cold dry north-westerly wind blowing from the Alps mountain region to the Rhone valley in France in Europe, is known as the Mistral wind. The Mistral wind can reach velocities of 130 km per hour.

Question 67. What is Bora wind?
Answer:

Bora wind

The very strong cold wind blowing over northern Italy and the eastern coast of the Adriatic sea in Europe during the winter, is known as Bora. These winds often reach a speed above 120 km/hour and create cloudless skies and cold weather conditions.

Question 68. What do you mean by weather and climate?
Answer:

Weather:

• The condition of temperature, air pressure, humidity, cloudiness, rainfall, snowfall, etc. of a certain place at a certain time is known as weather.
• The weather may persist for a few moments, a few hours, or a few days.

Climate:

• The average weather conditions persisting over an area for at least 35 years is known as the climate.
• In other words, the climate is the average of weather conditions over a long period of time.

Question 69. Why are easterly winds also called Trade winds?
Answer:

• In earlier days, ships used to sail across the oceans in the direction of the easterly winds for trade and commerce between the countries lying in the tropical region.
• As the winds helped in trade by helping the ships to move faster along the direction of the winds, they came to be known as Trade winds.

Question 70. What are anticyclones?
Answer:

Anticyclones

• Anticyclones are the opposite conditions of cyclones. In the Temperate and Frigid zones, over a small area of land, air may suddenly get cold and heavy and start moving downwards.
• This creates a deep high-pressure cell over the area. In such a condition, the winds start gushing out of the high-pressure region towards the adjacent low-pressure regions in circular motions.
• This is known as an anticyclone. Anticyclones rotate in a clockwise direction in the northern hemisphere and an anticlockwise direction in the southern hemisphere.

Question 71. What is the Buys Ballot’s Law?
Answer:

Buys Ballot’s Law

The Buys Ballot’s Law was proposed by the eminent scientist Buys Ballot during the 19th century. According to the law, if one stands with his back facing the wind direction in the northern hemisphere, air pressure felt on the left side is less than the pressure on the right side. The reverse condition is experienced in the southern hemisphere.

Question 72. What are the water column and sand column?
Answer:

• Water column: When a severe storm passes over an ocean, the cyclonic winds attract the ocean water and pull it upwards. Thus, the water rises like a pillar over the ocean. This is known as the water column.
• Sand column: When a cyclone blows over a desert region, it may attract the sand particles from the desert surface and draw them upwards, thus forming a big pillar of sand. This is known as the sand pillar.

Question 73. What is Sea breeze?
Answer:

Sea breeze

• The sea breeze is an example of periodic wind. In coastal regions during the daytime, the land gets heated and causes the air to get heated accordingly.
• This warm air becomes lighter and rises upward, thus creating a partial vacuum over land. The cool winds from the sea rush towards the land to fill up this vacuum.
• This is known as the ‘Sea breeze’. The maximum speed of the sea breeze occurs during the afternoon when the difference in temperature between land and sea is at its highest. [Winds blow from the sea to land].

Question 74. What is a land breeze?
Answer:

Land breeze

• Land breeze is an example of periodic winds in coastal regions. At night, the sea is warmer than the land. Thus, the air over the sea becomes warmer than the land.
• This warm air becomes lighter and rises upwards, creating a vacuum over the sea.
• Cool winds from the land then rush towards the sea to fill up the partial vacuum. This is known as a land breeze. The maximum speed of the land breeze occurs in the early morning [Winds blow from the land to the sea].

Question 75. What are geostrophic winds?
Answer:

Geostrophic winds

The thin streams of wind generated in the upper part of the atmosphere at 6-8 km altitude, parallel to the isobars are called geostrophic winds. Such winds are produced when the pressure gradient force and Coriolis force come into balance and the condition is called geostrophic balance.

Question 76. What do you mean by absolute humidity and relative humidity?
Answer:

Absolute humidity: The total amount of water vapor present in a unit volume of air at a particular temperature is known as absolute humidity. This is expressed in gm/kg.

Relative humidity: The ratio between the absolute humidity to the total amount of humidity that the volume of air can hold at that particular temperature, is known as relative humidity. This is represented in percentage (%).

Relative humidity = Absolute humidity at a particular temperature/Total humidity that the particular temperature 100

Question 77. How is Cyclonic rainfall caused?
Answer:

The rainfall caused by the formation of cyclones is known as cyclonic rainfall. If a low-pressure cell is created over land, winds from the surrounding high-pressure regions gush in circular motions toward the low-pressure cell to fill up the region. If the winds are moisture laden, they cause rainfall.

Processes:

1. In tropical regions, if a low-pressure cell is created, winds from high-pressure regions gush in and start rising upwards with great speed. These winds get cooled as they rise, and the water vapor condenses and causes torrential rainfall.
2.  In temperate regions, the cold winds and hot winds meet with each other along a margin known as the front. The hot winds lying below tend to rise upward while the heavy cold winds tend to move downwards. Thus, the water vapor present in hot winds comes in contact with the cold winds and condenses. This causes rainfall.

Question 78. Why does convectional rainfall occur in the equatorial region?
Answer:

In equatorial regions, the land gets highly heated and heats the air adjacent to it. Excessive evaporation occurs due to heat. The moisture-laden warm air tends to rise upward, where it meets cold air and starts condensing.

As the amount of water vapor is very high in the air, the air gets saturated very fast. During the afternoon, when the heat of the earth’s surface reduces considerably, the air cannot hold back the moisture, and drop it as rainfall. This phenomenon goes and repeats in a cyclical manner due to convection currents of air. Thus, convectional rainfall occurs in the equatorial region.

Question 79. Where is the monsoon climate seen in the world?
Answer:

The region lying between 10° and 25° latitudes in both the northern and southern hemispheres experiences a monsoon climate. The countries where monsoon climate is found are-

1. Asia: India, Bangladesh, Laos, Myanmar, Pakistan, Cambodia, Thailand, Vietnam, etc.
2. Africa: Liberia, Western Madagascar.
3. Australia: Northern part of Australia.
4. North America: South-eastern part of USA.

Question 80. List the characteristic features of monsoon climate.
Answer:

The characteristic features of monsoon climate are —

1. Four prominent seasons are experienced in this climate namely, summer, rainy autumn, and winter.
2. The temperature remains around 27-32°C in
3. The annual range of temperature is seasonal

Question 81. List the characteristics and features of a hot desert climate
Answer:

The characteristic features of a hot desert climate are—

1. The temperature rises as high as 40- 45°C in summer.
2. Winter temperatures occur between 15 and 21°C.
3. The diurnal range of temperature is very high.
4. Rainfall is very scanty in desert regions. Annual rainfall is about 10-15 cm.
5. In certain deserts, rainfall occurs at an interval of 2-4 years.

Question 82. Mention the areas of the world experiencing Mediterranean climate.
Answer: Mediterranean climate is found between 30 and 40° latitudes in both the northern and southern hemispheres.

The regions experiencing such climate are-

1. Europe: Portugal, Spain, Italy, Greece.
2. Asia: Western Turkey, Lebanon, Israel, Syria.
3. Africa: Egypt, Libya, Morocco, northern Algeria, Cape Town of southern Africa.
4. North America: Southern California.
5. South America: Chile.
6. Oceania: Southern and south-western coast of Australia.

Question 83. What are the characteristics of the Mediterranean climate?
Answer:

The characteristics of the Mediterranean climate are—

1. The temperature remains moderate throughout the year. The average temperature is around 20-27°C.
2. During winter temperature may drop to 5-10°C.
3. The average annual range of temperature is 15-17°C.
4. The summers are dry and the sky remains clear.
5. Rainfall occurs during winters due to the influence of the moist westerly winds causing cyclones. The average annual rainfall is 37-65 cm.

Question 84. Discuss the role of humidity in the air.
Answer:

The humidity influences the weather and climate of a region to a great extent.

The role of humidity in the air is—

1. Water vapor is the cause of any kind of condensation and precipitation.
2. Water vapor controls the temperature in the atmosphere.
3. The rate of evaporation remains very less if the presence of humidity in the air is high. If the presence of humidity is less, the rate of evaporation becomes high

Question 85.  Why is rainfall not produced by all the clouds?
Answer:

A cloud is created by condensation of water vapor on dust particles, sea salt nude, etc. in the upper atmosphere, and the accumulation of tiny droplets of water thus formed.

All clouds do not cause rainfall because of the following reasons—

1. The average diameter of water droplets forming the clouds is about 0.01 min. Unless they are at least 0.05 mm, they cannot fall down as rain. Even while falling down as rain, if the water droplets encounter a warm layer, they again evaporate back.
2. The tiny droplets of water must accumulate and join with each other to grow in size and fall as rain.
3. Condensation does not occur unless the relative humidity reaches 100%, hence no rainfall occurs

Question 86. Write down the characteristics of convectional rainfall.
Answer:

The characteristics of convectional rainfall are enough heat to cause evaporation, the air remains filled with a huge quantity of water-

1. Location: This type of rainfall occurs between 5 and 10° latitudes on either side of the equator

2. Time: This rainfall occurs the over the world. The equatorial region receives almost vertical rays of the sun, while the poles receive inclined rays. Thus, heat is maximum at the equator and goes on decreasing toward the poles. This leads to the year in the equatorial region, and at the beginning of summer in the temperate region.

3. Amount: On average, about 200-300 cm of rainfall occurs in the equatorial region

4. Name: Convectional rainfall occurs during the afternoon in the equatorial region every day. Hence, it is called the 4 o’clock rain.

5. Cloud: The rainfall is caused by cumulonimbus clouds.

6. Thunder: This type of rainfall causes thunder and lightning. E.g.—Java island has a record of 322 days of lightning in a particular year.

7. Nature of rainfall: Heavy downpour occurs for a short duration. After the rainfall, the sky becomes clear and bright.

Question 87. Identify the climate and the hemisphere of the region from the given temperature-rainfall diagram

Answer: The temperature-rainfall diagram shows—

1. The temperature curve is not very high.
2. The range of temperature is low.
3. The temperature graph remains the same throughout the year.
4. Temperature lies between 26 and 28°C.
5. Rainfall occurs throughout the year.

Conclusion: The diagram represents the equatorial climate. The temperature remains the same almost throughout the year. The little increase in temperature during the months of May and June shows that this is a diagram of the northern hemisphere.

Question 88. Identify the climate from the given temperature-rainfall diagram. Which hemisphere is depicted here?

Answer:

The temperature-rainfall diagram shows that:

1. May is the hottest month and January-February is the coolest month.
2. Most of the rainfall occurs during June, July, and August. A little rainfall occurs in winter.

Conclusion: The diagram depicts the tropical monsoon climate. May-June is very hot compared to other months. This depicts that this is a diagram of the northern hemisphere.

Question 89. Find out the climate depicted in the temperature-rainfall diagram. Detect the hemisphere being shown

Answer: The temperature-rainfall diagram shows that—

1. The temperature remains below the freezing point for the entire year except during June and September.
2. The temperature in January is -23°C.
3. The convex shape of the curve depicts that this is a diagram of the northern hemisphere.
4. Rainfall is very low, snowfall is profuse.

Conclusion: Chilling cold temperature, little rainfall, and the convex temperature graph indicate that this is a diagram of the Tundra region of the northern hemisphere

Question 90. What problems are caused by daily life?
Answer:

The problems caused by fog in our daily life are:

1. Fog reduces visibility. Thus, it becomes difficult to run trains, cars, and buses, especially on highways.
2. In urban and industrial regions, fog combines with the smoke of vehicles and chimneys, creating smog.
3. Fog is harmful to crops.
4. Fog influences the local climate of a place

Question 91. Identify the climate and hemisphere of the place from the given temperature-rainfall diagram.

Answer:

The given temperature-rainfall diagram shows that:

1. The temperature curve is concave. Thus, it definitely depicts a place in the southern hemisphere.
2. June, July, and August receive the maximum amount of rainfall.
3. The temperatures are found in July-August and are called the rain shadow area.

Question 92.  Identify the climate and hemisphere of the place from the given temperature-rainfall diagram.

Answer:

The temperature-rainfall diagram shows that:

1. The temperature curve is convex and the highest temperature recorded in July-August is 33°C.
2. Average annual rainfall is lower than 10 cm.

Conclusion: The diagram depicts locations in the northern hemisphere. Very hot summers and very less rainfall show that the place enjoys a hot desert climate.

Question 93. What do you mean by saturated air?
Answer:

Saturated air

• Air can hold different amounts of water vapor at different temperatures. At a particular temperature, if the air holds the maximum possible amount of water vapor, the condition of the air is said to be saturated.
• If the temperature of the air decreases, the moisture-holding capacity of the air also decreases and the extra water falls onto the earth’s surface as precipitation.
• But if the temperature of the air increases, the moisture-holding capacity of the air also increases and the air will not be saturated with the amount of water vapor it was holding previously.

Question 94. What is dew point
Answer:

Dew point

The temperature at which the air becomes saturated and the water vapor starts condensing is known as the dew point. At the dew point temperature, the relative humidity of air remains 100%. The water vapor starts changing into small droplets of water by condensation.

Question 95. What is the importance of relative humidity?
Answer:

The importance of relative humidity is—

1. Relative humidity gives an idea of the occurrence of rainfall, snowfall, dew, etc.
2. The rate of radiation of heat from the earth’s surface can be calculated from relative humidity.

Question 96. What is precipitation?
Answer:

Precipitation

• The water vapor present in the air on rising upward gets cooled gradually and starts condensing into very small crystals of ice in the upper atmosphere. These crystals of ice and tiny droplets of super-chilled water accumulate together to form clouds.
• As more and more ice crystals and water droplets accumulate, the cloud grows bigger in size and becomes heavy. Thus, they are pulled downwards towards the surface of the earth by gravitational force.
• This is known as precipitation. Precipitation may occur in the form of rain, sleet, drizzle, snow, hailstorm, etc

Question 97. What is humidity?
Answer:

Humidity

• The measure of water vapor contained in the air is known as humidity. Air can hold different amounts of humidity at different temperatures.
• If the air holds the maximum amount of water vapor possible at a particular temperature, it is said to be saturated. If the air can hold some more water vapor at that particular temperature, it is said to be unsaturated.

Question 98. What is absolute humidity?
Answer:

Absolute humidity

• The total amount of water vapor actually contained in a particular volume of air at a particular temperature is known as absolute humidity. It is expressed in gm/kg.
• If the temperature of the air changes, but the amount of water vapor in the air is kept constant, the relative humidity of the air will change, but the absolute humidity will remain the same.

Question 99. What is unsaturated air?
Answer:

Unsaturated air

The moisture-holding capacity of air depends upon its temperature. If at a particular temperature, the air contains less amount of water vapor than it can actually hold at that temperature, it is said to be unsaturated. An unsaturated air may become saturated if the temperature of the air is lowered. Similarly, saturated air may become unsaturated if the temperature is increased.

Question 100. What is snowfall?
Answer:

Snowfall

• Water vapor condenses and forms tiny ice crystals in the upper atmosphere as they rise upward along with air. These ice crystals accumulate together and form clouds.
• When they become much bigger and heavier, they start falling towards the earth’s surface as precipitation. If the air temperature is higher at lower altitudes the ice crystals melt and fall downwards as rain.
• But in mountainous regions and high altitudes, where the temperature is lower than the freezing point, the ice crystals need not melt and come down as snowfall.

Question 101. What is a hail storm?
Answer:

Hail storm

• Water vapor in the air rises upward along with air currents, cools down, and condenses, forming tiny crystals of ice. These crystals accumulate together and form clouds of ice.
• When the clouds thus formed become quite heavy, they start moving downward as precipitation.
• The warm air below forces some of the ice crystals to melt and fall as rain. But if the temperature suddenly drops after the occurrence of rain for some time, the ice crystals may come downward in solid form along with rainfall. This combination of ice crystals and rainfall is known as a hailstorm.

Question 102. How many types of rainfall are there? Name them.
Answer: Rainfall occurs due to condensation of water vapor present in the air. Rainfall can be classified into three types—

1. Convectional rainfall,
2. Orographic rainfall and
3. Cyclonic rainfall.

Question 103. What are warm and cold fronts?
Answer:

Warm and cold fronts

The sloping boundary that separates two contrasting air masses is known as the front.

1. A warm front is the gently sloping frontal surface along which the light warm air becomes active and gently rises over the cold dense air.
2. A cold front is the sloping frontal surface along which the dense cold air becomes active, but, being dense this air remains on the ground and forcibly uplifts the light warm air.

Question 104. What do you mean by occlusion?
Answer:

Occlusion

Occlusion is a stage in the life of a temperate cyclone. Since its genesis, after which the cyclone dies out. The cold air displaces the warm air from the ground and the warm air glides over the cold air.

The cold front moves faster than the warm front, ultimately the former overtaking the latter. The warm air is completely lifted up, the front thus formed is an occluded front and the cyclone dissipates thereafter.

Question 105. What is the relation between humidity and temperature?
Answer:

Relation between humidity and temperature

• Relative humidity is inversely related to temperature. In a particular volume of air, if the total amount of water vapor is kept constant, the relative humidity increases when the temperature of the air decreases.
• The relative humidity decreases if the temperature of the air increases.
• This is because the moisture-holding capacity of air is dependent on the temperature of the air.

Question 106. Why are rain shadow areas created on the leeward slope of mountains?
Answer:

• Moisture-laden winds cause rainfall on the windward slope of mountains.
• After showering rainfall, the winds become lighter and can easily cross the mountains, reaching the leeward side.
• On the leeward side, the winds have very little moisture, which fails to cause much rainfall.
• Moreover, these winds blow downward along the slopes of the mountain. As they reach lower altitudes they became warmer and moisture-holding capacity increases. Thus, they fail to cause rainfall with the little amount of water vapor present in the air. This turns the leeward slopes of the mountains into rain shadow areas.

Question 107. What is frost?
Answer:

Frost

• As the air temperature reaches the dew point, the atmospheric water vapor starts changing into tiny droplets of water called dew drops.
• If the air temperature falls below the dew point and reaches the freezing point, the dew drops tend to freeze into tiny crystals of ice. This is known as frost.

Question 108. On which factors does evaporation depend?
Answer:

Evaporation depends on the following factors—

1. Nature of landforms,
2. Height of water bodies,
3. Relative humidity of the air,
4. Wind speed.

The rate of evaporation is not the same all over the earth. It is highest near the tropical desert regions.

Question 109. Name the instrument by which humidity can be measured.
Answer:

1. Humidity is measured with the help of a hygrometer or rain gauge.
2. The relative humidity is measured by the Six’s maximum and minimum thermometer.
3. Recently, numerous kinds of hygrometers have been invented, that measure humidity.

The common types of such hygrometers are-

1. Dew point hygrometer,
2. Hair tension hygrometer,
3. Resistive hygrometer, etc.

Question 110. Why does fog occur in urban areas and industrial zones?
Answer:

• The sky in the urban centers and industrial zones remain filled with suspended particles of carbon, dust, and other aerosols.
• During the night, when these particles get cooled, the water vapor present in the atmosphere condenses on them and forms many tiny water droplets that remain suspended in the air.
• This is known as fog. Fog reduces visibility considerably.

Example:  The iron and steel centers of Durgapur and Jamshedpur.

Question 111. List the significance of humidity in the air.
Answer:

The importance of humidity in the air is as follows—

1. Humidity helps in conducting the water cycle.
2. Condensation occurs due to the presence of water vapor.
3. The heat radiated by the earth is arrested by the water vapor.
4. Too much relative humidity makes the air very moist and feels very uncomfortable. Lack of humidity (in winter) makes the air very dry.

Question 112. What is the lower course or delta course of a river?
Answer:

Lower course

• The course where the river flows through a plain land till it reaches the mouth of the river in a sea, lake, or any other depression, is called the lower course of the river.
• This course spreads through the delta region. E.g.-The portion of the river Ganga, lying between south of Rajmahal hills to the mouth in the Bay of Bengal is known as the lower course of the river.

Long Question And Answers

Question 19. What is the water cycle? How is water transported through the water cycle?
Answer:

Water cycle

The circulation of water from the earth to the atmosphere and back occurring in a cyclical manner is known as the water cycle. Water escapes from the earth s surface, oceans, and other water bodies and underground into the atmosphere in the form of water vapor.

Later, this water comes back to the earth’s surface in solid or liquid form. Thus, the balance of water present in the atmosphere, lithosphere, and hydrosphere is maintained by the water cycle.

 

Transportation of water:

1. Evaporation: The sea is the main source of free water or open water. Other sources of water are rivers, lakes, ponds, canals, etc. Water evaporates from these water bodies and also from the underground and from plants and reaches the atmosphere as water vapor.
2. Condensation: The water vapor present in the atmosphere condenses on the dust and salt particles present in the atmosphere and changes back to water droplets or ice crystals. These droplets accumulate together and fall as rain or snow when the temperature permits.
3. Precipitation: The tiny water droplets or ice crystals formed in condensation, accumulate together, become heavy, and tend to fall downward. This is known as precipitation. It may occur in the form of rain, snow, hail, drizzle, etc.

Thus, the water cycle comprises evaporation, condensation, and precipitation, without which the circulation of water would not have been possible.

Question 7. Where is the equatorial climate formed in the world?
Answer:

Equatorial climate is formed within 5°-10° latitude in both northern and southern hemispheres.

The regions where the equatorial climate is found are as follows—

1. Asia: India, Bangladesh, Laos, Myanmar, Pakistan, Cambodia, Thailand, Vietnam, etc.
2. Africa: Liberia, Western Madagascar.
3. Australia: Northern part of Australia.
4. North America: South-eastern part of USA.

 

Question 8 List the characteristic features of equatorial climates.
Answer:

The characteristic features of the equatorial climate are—

1. The temperature remains high throughout the year. The diurnal range of temperature is very small. There is no change of seasons.
2. The average annual temperature is about 27°C, and the annual range of temperature is about 2°-3°C.
3. The sky remains covered with clouds during the afternoon due to the excessive rate of evaporation.
4. Rainfall occurs every day during the afternoon. This is also known as 4 o’clock rain.
5. Cyclones or heavy storms do not occur here due to the presence of the calm region nearby experienced in this climate namely, summer, rainy season, autumn, and winter.

Question 9 Where hot desert climate found in the world?
Answer: Hot desert climate is found between 15 and 35° latitudes in both the northern and southern hemispheres.

The regions where the hot desert climate is found are—

1. Africa: Sahara, Kalahari and Namib deserts
2. Asia: Saudi Arabia, Lebanon, Iran, the Thar desert of India, and Pakistan.
3. Oceania: Australian deserts.
4. North America: Arizona desert.
5. South America: Atacama desert.

Question 33. What are pressure cells?
Answer:

Pressure cells

The pressure belts sometimes break into small portions and lie over small regions in the shape of cells. This occurs due to differential.

This occurs due to differential heating of water and landmass and hence the development of high-pressure and low-pressure conditions on land and water accordingly.

The location of the continents and oceans and their shapes lead to the formation of a number of pressure cells in the northern hemisphere compared to the south.

Question 36. What do you mean by pressure gradient?
Answer:

Pressure gradient

The isobars are imaginary lines to join places having the same pressure conditions. The pressure gradient refers to the difference in pressure conditions over a unit distance in an area. It is measured as the force per unit area in a region.

pressure gradient = Vertical Interval (VI)/Horizontal Equivalent (HE)

Where, VI = Difference in pressure between two places HE = Actual horizontal distance between the two places
In a weather map,

1. The pressure gradient is high or steep if the Pressure gradient = isobars lie very close to each other over a period of time
2. The pressure gradient is gentle when the isobars lie far away from each other.
3. The pressure gradient will become steeper with increasing differences in air pressure between the two places.
4. Winds blow with greater speed if the pressure gradient is steep, while winds blow with less speed if the pressure gradient is normal or gentle.

Question 26. What are mountain breeze and valley breeze?
Answer:

Mountain breeze: In the mountainous regions during the night, the air cools down and becomes heavy due to radiation of heat, and slips downwards along the slope.

This causes the warm air to stay above the cold air. These breezes or winds are known as katabatic winds.

 

Valley breeze:

In mountainous regions during the daytime, air starts getting heated, becomes lighter, and tends to rise along the slopes of the mountain valleys and yield precipitation on reaching greater heights. These are known as anabatic winds or valley breezes or winds. Valley breezes cause the formation of clouds in the upper parts of the mountains.

Chapter 2 Atmosphere Topic 4 Humidity And Precipitation

Question 1 How does rainfall occur?
Answer:

Rainfall occurs through the following processes

Air Contains some account of water vapor, Which makes the air light and it tends to rise.

• As the moist air rises upward, pressure decreases, and the air starts cooling down.
• Gradually, the air in the upper atmosphere starts getting saturated, as the moisture-holding capacity of the air decreases with an increase in altitude. When the temperature of the saturated air falls below the freezing point, the extra water vapor starts condensing on the dust particles, carbon, and salt particles floating in the air, forming tiny droplets of water and ice crystals.
• The water droplets thus formed collide with each other and adhere to form bigger droplets.
• These bigger droplets become heavy and cannot float in the air anymore.
• Thus, they fall as rainfall. If the temperature in the lower layers is quite low, snowfall may occur instead of rainfall.

Question 2 Describe the different types of rainfall. OR’ Discuss the difference between rain, a and give examples
Answer:

Rainfall is classified into three types according to their mode of origin:

 

 

Rainfall	concept	Method	Example
Correctional rainfall	The moisture-laden air rises upward due to excessive heating of the earth’s surface, cools down, and causes rainfall.	In hot regions, where there are enough water bodies, the water evaporates in huge amounts due to excessive heat. This rises upward along with the air, gets cooled, and condenses on the dust and salt particles, forming clouds. In the afternoon, when the surface temperature falls, the air gets saturated and cannot hold back the water droplets in the clouds. Thus, they come down as rainfall. This process goes on in a cyclical form, and so is called convectional rainfall.	Convectional rainfall occurs In the equatorial region throughout the year in the afternoon. It is also known as the 4 o’clock rain.
Orographic	The moisture-laden air collides with the hill slopes, it rises and gets cooled and causes rainfall.	If the moisture-laden air is obstructed by high landforms in its path, it rises upward. Here, it gets cooled and condenses to cause enough rainfall. After shedding water, the air becomes lighter and rises higher. As it crosses the mountains and blows over the leeward side, due to insufficient moisture very little rainfall occurs. Thus, this region becomes a rain shadow area. As the air slips down the slope of the leeward side, its temperature and moisture-holding capacity increase. Thus, the chances of rainfall decrease even more. enough rainfall. After shedding water, the air becomes lighter and rises higher. As it crosses the mountains and blows over the leeward side, due to insufficient moisture very little rainfall occurs. Thus, this region becomes a rain shadow area. As the air slips down the slope of the leeward side, its temperature and moisture-holding capacity increase. Thus, the chances of rainfall decrease even more.	The western slope of the Western Ghats, foothills of the Himalayas, the Mawsynram, and Cherrapunjl in Meghalaya all receive rainfall due to the southwest monsoons.

 

Convention Rainfall:

Orographic Rainfall:

Cyclonic Rainfall:

 

Question 3 How is rainfall caused by temperate cyclones?
Answer: In temperate regions, two air masses of opposite characteristics meet each other along a front. The cold and dry air coming from the northeastern side meets the warm moist air coming from the southwestern side along a front.

The warm air enters the cold air from below and the cold air enters the warm from the top. The place where the warm air meets the cold air is known as the warm front. The place where the cold air hits the warm air from the back is known as the cold front.

Rainfall at the warm front: The warm air rises upward through the cold air. In this process, the water vapor present in the warm air comes in contact with the cold air and condenses. This causes rainfall.

 

Rainfall at the cold front: The cold air pushes the warm air upward from the back. Thus, the warm air rises up and cools down and the water vapor present in the warm air starts condensing. This causes heavy rainfall with thunder and lightning.

Regions: Rainfall from temperate cyclones occur in many places in Europe during the winter season.

Question 4 How does rainfall occur from tropical cyclones?
Answer: Tropical cyclones occur between 5-20°N and S latitudes during summers. Excessive heating of the region causes the development of low-pressure cells on the land.

Cool and heavy air from the adjacent areas gushes with great speed toward the low-pressure cell in circular motions. This air gradually rises upward in a circular motion and starts becoming cooler.

The water vapor present in the air condenses. The center or eye of the cyclone remains calm, but winds from the surrounding areas rush with such speed that they cause severe storms along with heavy rainfall.

Example: Cyclones originate in the Bay of Bengal when the eastern coastal regions of India get heated in the summer season and develop low-pressure cells. This type of cyclone forms when the warm and moist southwest monsoon winds meet with the hot dry winds on land. Such a weak cyclone may cause rainfall for a few days continuously.

Question 5 Classify precipitation.
Answer:

Precipitation:

The warm and moist air tends to rise upward and the water vapor condenses to form tiny droplets of water or ice crystals.

These crystals and droplets come close and adhere to each other, thus growing in size. When they grow quite big, they cannot float in the air, and thus fall on the earth’s surface due to gravitational force.

This is known as precipitation. Precipitation may occur in two forms—

1. Liquid and
2. Solid.

1. Liquid:

• The tiny droplets of water formed due to condensation of water vapor adhere to each other and form clouds.
  When the water droplets grow bigger in size, they come down due to gravity.
• This precipitation in the liquid form is known as rainfall. Rainfall can be of three types— Convectional, Orographic, and Cyclonic.

2. Solid:

1. Snowfall: In higher latitudes or cold regions, the moisture in the air condenses in the upper atmosphere and forms ice crystals. These ice crystals come down as snowfall when they grow bigger in size.
2. Hailstorm: The upward-moving stormy air drives the moisture-laden air to great heights in the atmosphere, where they cool down and condenses to form ice crystals.

These ice crystals become heavy and tend to fall downward. They are once again driven upward by the stormy winds, where they collect more water droplets, freeze and become bigger and heavier.

These large crystals of ice then fall on the earth’s surface along with rainfall as hailstorms. The hailstones that fall with hailstorms have a diameter of 5 to 50 mm.

3. Sleet:

• In cool temperate regions, the rain drops cool down while falling through the cooler layers of the atmosphere, and tend to freeze.
• Thus, precipitation occurs in the form of very small granules called sleet, which have a diameter of less than 5 mm.

Question 6 Discuss the major characteristic ‘and features of Tropical Monsoon climatic regions.
Answer: The tropical monsoon climate extends from 10°-25° latitudes in both hemispheres. In India and Pakistan, the influence of this climatic region extends up to 30°N latitude in the north.

Climatic characteristics:

The major characteristics of the tropical monsoon climatic region are as follows—

1. Wet summers and dry winters:

• In monsoon climatic regions during the summer season, the wet monsoon winds while blowing over the ocean pick up moisture and cause rainfall. But during the winter season
• The cold dry winds blow from the land and do not cause rainfall. Hence, the weather remains dry.

2. Two oppositely blowing winds during summer and winter:

In the monsoon climatic regions, during summer, winds blow from the south while during winter winds blow from the north.

For example:

• In the Indian subcontinent during summer, wet southwest monsoon winds and in winter the dry northeast monsoon winds blow. This reversal of wind system is a typical feature of monsoon climate.
• It can be mentioned here that the word monsoon is derived from the Arabic word ‘Muslim’, meaning season.

3. Moderate temperature:

• Monsoon climatic regions experience 30-32°C temperature in summer and 19-22°C temperature in winter.
• In summer the wet monsoon winds bring rainfall and give relief from sweltering heat conditions.

4. Moderate rainfall:

• In monsoon regions average annual rainfall varies from 75-100 cm.
• However, topography and distance from the sea have a profound influence on the amount of rainfall.

For example:

Mountainous and coastal areas receive very high amounts of rainfall, nearly 150-200 cm.

• In India, Mawsynram lying on the southern slope of the Khasi hills in Meghalaya receive about 1187 cm of rainfall annually.
• But, Shillong lying on the leeward side of the Khasi hills receives only 250 cm of rainfall annually.

Again, Allahabad located far away from the coast receives about 100 cm of rainfall annually.

5. Change of seasons:

The change of seasons is one of the important characteristics of monsoon climate. The onset and retreat of two opposite monsoon winds cause a change of seasons.

For example in the northern hemisphere:

• The cold, dry season lasting from December to February is called winter,
• The hot, dry season from March to May is known as summer,
• The hot, wet season from June to September is called the season of south-west monsoon or rainy season,
• October and November is the season of retreating southwest monsoon or autumn. In the southern hemisphere, the opposite seasons occur during the same period.

Question 25. What are the differences between the land breeze and the sea breeze?
Answer:

The differences between the land breeze and sea breeze are:

Question 26. What are the differences between cyclone and anticyclone? OR, Mention four differences between cyclones and anticyclones.
Answer:

The differences between cyclone and anticyclone

Question 3. How are clouds formed?
Answer:

The water vapor present in warm air rises upward along with the air currents. As it gains altitude, it starts becoming cooler. The moisture-holding capacity of the air decreases with a fall in temperature.

Thus, the air gets saturated at the dew point. The water vapor starts condensing on the dust particles, sea salt nuclei, and tiny ice crystals present in the air and forms very tiny droplets of water or ice. These droplets accumulate together to form clouds. When the clouds become very heavy, they cannot hold the water anymore, and drop them as precipitation.

Question 16 Why does temperature decrease with an increase in altitude in the Troposphere?
Answer:

Temperature decreases with the increase of altitude in the Troposphere at the rate of 6.4° C with every 1000 m altitude. This is known as a normal lapse of temperature.

This happens because of the following reasons—

1. Less radiation received: The atmosphere does not get heated directly. It gets heated up by the radiation received from the surface of the earth. Thus, the lower part of the atmosphere coming in direct contact with the surface of the earth gets more heat than the portion lying above.

2. Less dense air: The layers of air are denser near the earth’s surface and become lighter with increasing altitude. Hence, the upper layers receive less heat.

3. Less heat absorbing capacity: The lower layer of the atmosphere contains more water vapor, dust particles, and sea salt nuclei than the layers above and hence heat retentive and heat absorbing capacity considerably decrease with the increase of altitude.

4. Thin layer of air: The atmosphere gradually thins out with an increase in altitude. For this reason, the air in the upper layers expands quickly and cools rapidly by the release of radiation.

Question 22 Differentiate between weather and climate.
Answer:

The difference between weather and climate are –