Atmosphere and Climate — NCERT Solutions

The atmosphere is a mixture of gases. The two main gases are nitrogen and oxygen. In smaller amounts, it also contains carbon dioxide, argon, helium, neon, krypton, xenon, ozone, hydrogen, and it has water vapour and tiny dust particles. Water vapour usually ranges from 0.1% to 0.4%.

The atmosphere has five main layers, and each affects Earth in a different way. The troposphere is the lowest layer and is the most important for life because it contains the air we breathe, most water vapour, clouds, and nearly all weather phenomena like rain, fog, and hail. The stratosphere lies above it and contains the ozone layer, which protects life by filtering harmful ultraviolet rays from the Sun; it is also good for flying aeroplanes because the air is calm and cloud-free. The mesosphere is the layer where temperature decreases with height and most meteors burn up. The thermosphere absorbs X-rays and short-wave ultraviolet radiation, so its temperature rises sharply; it also helps radio transmission and is where auroras occur. The exosphere is the outermost layer, with very thin air, where light gases like hydrogen and helium escape into space. Together, these layers protect Earth, control weather, and support life.

The monsoon is caused by the seasonal reversal of wind direction. In India, the main mechanism is the unequal heating of land and sea. During summer, the land heats up faster than the surrounding oceans, so a low-pressure area forms over the Indian subcontinent while the ocean remains cooler with high pressure. Winds then blow from the high-pressure ocean towards the low-pressure land, bringing moist air and rainfall. This is the south-west monsoon. In winter, the land cools faster than the sea, so high pressure forms over land and winds blow from land to sea as the north-east monsoon. These winds usually do not bring rain to most of India, but after crossing the Bay of Bengal they pick up moisture and give rainfall to parts of the south-east coast.

We can reduce our carbon footprint by making simple changes in daily life. We should save electricity by switching off lights, fans, and appliances when not in use. We should use public transport, carpool, walk, or cycle instead of using private cars for short distances. We should reuse, recycle, and avoid single-use plastics. We should also save water and use it judiciously. Planting trees, using renewable energy, protecting forests, and adopting a more sustainable lifestyle also help reduce greenhouse gas emissions.

Strong winds can cause problems in many situations. For example, they can make it hard to walk or cycle, blow away dust and dry leaves, and make it difficult to use umbrellas. During storms, strong winds can uproot trees, damage roofs, and break electric wires. They can also make travel unsafe for boats, bicycles, buses, and trains, and may damage crops and house property. In some places, strong winds can spread fires or make it difficult to keep things in place outdoors.

Plants need nitrogen for healthy growth. They cannot use nitrogen gas directly from the air in most cases, so they depend on nitrogen in the soil, which helps them form proteins and other important substances. That is why nitrogen is useful for plants.

Monsoon affects people's lives in many ways. It is very important for agriculture because farmers depend on monsoon rain for sowing and growing crops. A good monsoon gives enough water in rivers, reservoirs, and wells and supports food production. It also affects daily life, transport, festivals, and employment, especially in rural areas. But too much rain can cause floods, while too little rain can lead to droughts. So monsoon has a strong effect on the economy, livelihoods, and routine life of people around us.

The atmosphere is the blanket of air surrounding the Earth. It is held around the Earth by gravity and is a mixture of gases in different proportions, which are vital for life. Its composition includes mainly nitrogen and oxygen, with smaller amounts of carbon dioxide, argon, helium, neon, krypton, xenon, ozone, hydrogen, along with water vapour and dust particles. A pie diagram would show nitrogen as the largest part, oxygen as the second largest, and the remaining gases, water vapour, and dust as very small portions.

The Indian Meteorological Department recognises four main seasons in India: Winter, Summer or pre-monsoon, Monsoon or rainy (advancing monsoon), and Post-monsoon (retreating monsoon).

We do not feel the pressure of the atmosphere because air presses on us from all sides, and our bodies exert an equal counter-pressure. The pressure inside our bodies balances the atmospheric pressure outside, so the two forces cancel each other out. That is why we usually do not notice atmospheric pressure.

Aeroplanes fly in the stratosphere because this layer is free of clouds and weather disturbances. The air is relatively stable there, so flying is smoother and safer than in the troposphere, where most weather changes occur.

• The troposphere is the lowest layer. It contains the air we breathe, most water vapour and clouds, and nearly all weather phenomena. In this layer, temperature decreases with increasing altitude.
• The stratosphere lies above the troposphere. It is free of clouds and weather disturbances, contains the ozone layer, and is suitable for flying aeroplanes. The ozone here protects us from harmful ultraviolet rays.

So the main differences are in weather, temperature pattern, and ozone protection.

• The south-west monsoon is the summer monsoon. It blows from the sea to the land between June and September, bringing moist air and rainfall. It is caused by the low pressure over the heated land and high pressure over the cooler ocean.
• The north-east monsoon is the winter monsoon. It blows from the land to the sea from October to February. It is usually cold and dry, so it does not bring rain to most of India, though after crossing the Bay of Bengal it gives rain to parts of the south-eastern coast.

Arrange the stations by distance from the equator, i.e. by latitude from lower to higher. The latitudes are:

• Thiruvananthapuram: 8°29'N
• Chennai: 13°4'N
• Bengaluru: 12°58'N
• Kolkata: 22°34'N
• Shillong: 24°34'N
• Mumbai: 19°N
• Nagpur: 21°9'N
• Jodhpur: 26°18'N
• Delhi: 29°N
• Leh: 34°N

So the order from nearest to farthest from the equator is: Thiruvananthapuram, Bengaluru, Chennai, Mumbai, Nagpur, Kolkata, Shillong, Jodhpur, Delhi, Leh.

The two stations with the most extreme climate are Leh and Delhi. Leh has very low temperatures and a large annual range because it is at a very high altitude. Delhi also has a large seasonal difference between hot summers and cool winters, so it has an extreme climate compared with coastal places.