Atmosphere and Climate - Social Science Class 9 In English

Chapter 3. Atmosphere and Climate

NCERT Textbook Questions and Answers

Question 1. What is atmosphere? Explain its composition with the help of a pie diagram.

Answer: The atmosphere is the blanket of air surrounding the Earth. It is held around the Earth by gravity and consists of a mixture of different gases in various proportions. It is essential for the survival of all living beings.

The major components of the atmosphere are:

Besides these gases, the atmosphere also contains varying amounts of water vapour and tiny dust particles. Water vapour generally ranges from about 0.1% to 0.4% and plays an important role in cloud formation and precipitation.

For the pie diagram: The largest sector should represent nitrogen (78%), followed by oxygen (21%). The remaining very small sectors should represent argon, carbon dioxide, and other gases.

Question 2. Draw a labelled diagram of the structure of atmosphere.

Answer: The atmosphere is divided into five major layers on the basis of changes in temperature and air density with increasing altitude.

• Troposphere – Lowest layer; most weather phenomena occur here.
• Stratosphere – Contains the ozone layer and is relatively free from major weather disturbances.
• Mesosphere – Most meteorites entering the atmosphere burn up here.
• Thermosphere – Temperature rises rapidly; auroras occur here.
• Exosphere – Uppermost layer with extremely thin air.

Suggested labelled diagram:

Question 3. Which are the four main seasons of India?

Answer: According to the Indian Meteorological Department (IMD), the four main seasons of India are:

1. Winter Season – December to early April
2. Summer or Pre-monsoon Season – April to June, or up to July in north-western India
3. Monsoon or Rainy Season – June to September
4. Post-monsoon or Retreating Monsoon Season – October to December

The Himalayan states experience two additional seasons—autumn and spring—because of their more temperate conditions.

Question 4. Why do you not feel the pressure of the atmosphere?

Answer: The atmosphere exerts pressure on our bodies from all sides. However, we do not feel this pressure because the pressure inside our bodies is also approximately equal to the atmospheric pressure outside. These pressures balance each other, so there is no significant net pressure that we feel.

Question 5. In which layer of the atmosphere do aeroplanes fly and why?

Answer: Aeroplanes generally fly in the stratosphere, especially in its lower part.

The stratosphere is relatively free from clouds and major weather disturbances. Therefore, flying in this layer provides comparatively stable atmospheric conditions and helps aircraft avoid much of the turbulence and weather activity found in the troposphere.

Question 6(a). Distinguish between the troposphere and stratosphere.

Question 6(b). Distinguish between the south-west monsoon and north-east monsoon.

Question 7. Table 3.3 shows the average monthly temperatures and rainfall amounts for 10 representative stations. Study these figures and convert them into temperature and rainfall graphs.

Answer: The textbook asks students to prepare graphs using the temperature and rainfall data given in Table 3.3. The graph should contain months from January to December on the horizontal axis.

The monthly temperature should be represented using the temperature scale, while monthly rainfall should be represented using the rainfall scale.

The textbook has already provided the example graph for Delhi as Fig. 3.14. Similar graphs can be prepared for the remaining stations using the data in Table 3.3.

General observations from the data:

• Temperature varies considerably between the stations.
• Leh experiences very low winter temperatures.
• Thiruvananthapuram has relatively small annual temperature variation.
• Jodhpur has low annual rainfall.
• Shillong receives very high rainfall.
• Chennai receives a large proportion of its rainfall during October and November.
• Mumbai receives very heavy rainfall during the south-west monsoon months.

Question 7.1. Now look at Table 3.3 again. Re-arrange the 10 stations according to their distance from the equator.

Answer: The stations can be arranged from closest to the equator to farthest from the equator as follows:

1. Thiruvananthapuram – 8°29'N
2. Bengaluru – 12°58'N
3. Chennai – 13°4'N
4. Mumbai – 19°N
5. Nagpur – 21°9'N
6. Kolkata – 22°34'N
7. Shillong – 24°34'N
8. Jodhpur – 26°18'N
9. Delhi – 29°N
10. Leh – 34°N

Question 7.2(a). Find out two stations with the most extreme climate.

Answer: Leh and Jodhpur show the most extreme climatic conditions among the stations given in the table.

Leh has very low winter temperatures and a large annual temperature range. Jodhpur has very low annual rainfall and experiences high summer temperatures.

Question 7.2(b). Find out two stations influenced by retreating monsoons.

Answer: Chennai and Thiruvananthapuram are strongly influenced by the retreating/north-east monsoon.

This is particularly clear from their rainfall pattern. Chennai receives its highest rainfall in October and November, while Thiruvananthapuram also receives substantial rainfall during October and November.

Question 7.2(c). Find out the two hottest stations in the months of (i) February and (ii) June.

Answer:

(i) February: The two hottest stations are:

1. Thiruvananthapuram – 27.3°C
2. Chennai – 25.7°C

(ii) June: The two hottest stations are:

1. Jodhpur – 33.9°C
2. Delhi – 33.3°C

Question 7.3(a). Why does Shillong experience more rainfall than Kolkata?

Answer: Shillong is located at a much higher altitude and is surrounded by the hills of the Meghalaya region. Moisture-laden monsoon winds are forced to rise when they encounter these hills. As the air rises, it cools and condensation occurs, resulting in heavy rainfall.

Kolkata also receives substantial monsoon rainfall, but Shillong's geographical setting and relief favour much heavier rainfall. The annual rainfall given in Table 3.3 is about 225.3 cm at Shillong, compared with about 162.5 cm at Kolkata.

Question 7.3(b). Why does Delhi receive more rainfall than Jodhpur?

Answer: Delhi receives more rainfall because it is reached by the moisture-bearing monsoon winds that travel into northern India. Jodhpur lies farther west in a much drier region, where the monsoon winds have less moisture available to produce rainfall.

The difference is clear from Table 3.3: Delhi receives about 67.0 cm of annual rainfall, whereas Jodhpur receives only about 36.6 cm.

Question 7.4(a). Why does Thiruvananthapuram have an equable climate?

Answer: Thiruvananthapuram is located close to the equator and near the sea. The sea moderates temperature because it heats and cools more slowly than land. As a result, the difference between summer and winter temperatures is relatively small.

The data in Table 3.3 supports this observation. Temperatures at Thiruvananthapuram remain relatively high and show only a small annual range, from about 26.2°C to 28.7°C.

Question 7.4(b). Why does Chennai have more rainfall only after the fury of the monsoon is over in most parts of the country?

Answer: Chennai receives a large part of its rainfall from the north-east or retreating monsoon. During this period, the north-east monsoon winds pass over the Bay of Bengal and pick up moisture before reaching the south-eastern coast.

Therefore, while the south-west monsoon is retreating from most parts of India, Chennai receives substantial rainfall during October and November.

The rainfall data supports this: Chennai receives about 30.6 cm in October and 35.0 cm in November, much higher than during several earlier months.

Question 7.4(c). Why does Leh have moderate precipitation almost throughout the year?

Answer: Leh is located at a very high altitude in the Himalayan region. Its high mountainous setting limits the amount of moisture-bearing monsoon rainfall it receives. It also receives some precipitation from other weather systems during different parts of the year.

The rainfall data in Table 3.3 shows small amounts of precipitation distributed across most months. Its annual rainfall is only about 8.5 cm, showing that the precipitation is limited but spread across much of the year.

Question 7.5. Despite these differences across regions, can you observe any substantial evidence to conclude that the monsoons provide a very strong framework, lending overall climatic unity to the whole country?

Answer: Yes. Despite considerable regional variations in temperature and rainfall, the monsoon provides an important common climatic framework for India.

The arrival, progress, and retreat of the monsoon influence rainfall patterns across a large part of the country. Agriculture, water availability, rivers, reservoirs, employment, transport, festivals, and daily life are closely connected with the monsoon.

The different rainfall patterns of Mumbai, Kolkata, Delhi, Chennai, Shillong, and other stations show regional diversity, but the seasonal rhythm of the monsoon connects these regions within a broader climatic system.

Thus, the monsoon contributes significantly to the overall climatic unity of India.

Question 8. Collect pictures of houses and clothing of people from different regions of India. Examine whether they reflect any relationship with the climatic conditions or the relief of those regions.

Answer: Yes. Houses and clothing in different regions of India often reflect the local climate and relief.

In cold mountainous regions, houses are generally designed to provide protection from low temperatures and snowfall, while people wear woollen and other warm clothing.

In hot regions, houses may have features that allow ventilation and reduce the effect of heat. People often prefer light and loose clothing.

In high-rainfall regions, houses may have sloping roofs so that rainwater can drain quickly.

In flood-prone areas, houses may be raised above the ground to reduce the impact of floodwater.

Thus, local climate, rainfall, temperature, and relief influence the design of houses and the clothing people use.

Additional NCERT Activity – Monsoon and Daily Life

Question. Describe in your own words how monsoon affects the lives of the people around you.

Answer: The monsoon has a major influence on everyday life. Farmers depend on monsoon rainfall for sowing and growing crops. Adequate rainfall helps maintain water in rivers, reservoirs, and wells.

Monsoon rainfall also affects transport, employment, festivals, food production, and water availability. Excessive rainfall can cause floods and damage crops and infrastructure, while weak rainfall can lead to drought and water shortages.

Therefore, the monsoon influences both the economy and the daily life of people.

NCERT Activity – Climate Data Analysis

Question. What broad conclusions can be drawn from the temperature and rainfall data of the ten stations?

Answer: The data shows considerable climatic diversity across India.

• Southern stations such as Thiruvananthapuram have relatively small annual temperature variations.
• Leh has very low winter temperatures and a large annual temperature range.
• Jodhpur has the lowest annual rainfall among the stations listed.
• Shillong has the highest annual rainfall among the stations listed.
• Mumbai receives very heavy rainfall during the south-west monsoon.
• Chennai receives its highest rainfall during October and November.
• Delhi and Jodhpur experience high summer temperatures.
• Altitude, latitude, distance from the sea, relief, and monsoon patterns contribute to the differences among the stations.

NCERT Activity – Climate and Lifestyle

Question. How do climatic conditions influence the lifestyle of people in different parts of India?

Answer: Climatic conditions influence people's clothing, houses, occupations, agriculture, food habits, and daily activities.

People living in cold regions generally require warm clothing and houses designed to retain heat. In areas receiving heavy rainfall, houses often require suitable roofs and drainage arrangements. In hot regions, ventilation becomes important.

Agriculture is also closely related to climate. Areas receiving sufficient monsoon rainfall can support different crops, while dry areas require irrigation or drought-resistant crops.

Thus, climate is closely connected with the way people live and adapt to their surroundings.