Experts have designed these Class 9 SST Notes and NCERT Class 9 SST Chapter 3 Atmosphere and Climate Notes for effective learning.
Class 9 Atmosphere and Climate Notes
Class 9 SST Chapter 3 Atmosphere and Climate Notes
Class 9 SST Chapter 3 Notes – Atmosphere and Climate Notes Class 9
- The atmosphere is a blanket of air held around the Earth by gravity.
- It is made of gases essential for life, protects us from harmful solar radiation, regulates the Earth’s temperature by preventing heat from escaping into space, and drives weather and climate through factors like temperature, humidity, and air pressure.
Composition And Structure Of The Atmosphere
Composition of the Atmosphere
- The Earth’s atmosphere is made up of a mixture of different gases.
- Nitrogen (78%) and oxygen (21 %) are the two main and abundant gases in Earth’s atmosphere, and both are essential for life.
- Smaller amounts of gases such as argon, helium, neon, carbon dioxide, krypton, xenon, hydrogen, and ozone are also present in the atmosphere.
- In addition, the atmosphere contains water vapour, usually ranging from 0.1% to 0.4%, which plays a key role in cloud formation and precipitation, along with tiny dust particles.
- The atmospheric composition differs at different altitude.
Structure of the Atmosphere
- The atmosphere is structured in layers, defined by changes in temperature and density as altitude increases.
- Air is densest near the Earth’s surface and becomes thinner with height.
- The atmosphere consists of five main layers extending from the Earth’s surface to outer space.
Troposphere: The troposphere is the lowest and most important layer of the atmosphere, with an average height of about 12 kilometres
Mesosphere: The mesosphere lies above the stratosphere and extends up to about 80 kilometres.
- In this layer, the temperature drops as altitude increases.
- It is also the region where most meteorites entering from space bum up.
- In the troposphere and mesosphere, temperature decreases as altitude increases.
Thermosphere: The thermosphere extends from about 80 to 700 kilometres above Earth’s surface.
- In this layer, the temperature rises rapidly with altitude because gas molecules absorb the Sun’s X-rays and short-wave ultraviolet radiation.
- The thermosphere plays a vital role in radio transmission by reflecting radio waves back towards Earth.
- A part of this layer, known as the ionosphere.
- Additionally, the spectacular auroras—the northern and southern lights—occur in the thermosphere.
- The word aurora comes from Latin, meaning “dawn,” named after the Roman goddess of dawn.
- Auroras are colourful lights seen near the poles, caused when the solar wind—charged particles from the Sun—interacts with atmospheric gases, making them glow in different colours.
- They are called the Aurora Borealis in the Northern Hemisphere and the Aurora Australis in the Southern Hemisphere.
Exosphere: The exosphere is the outermost layer of the atmosphere and contains extremely thin air.
Light gases such as helium and hydrogen gradually escape into space from this layer because of weak gravity. Together, all atmospheric layers play an vital role in atmospheric processes and influence the Earth’s weather and climate.
Air presses on our body from all sides, but we do not feel it because our body pushes back with equal pressure.
Weather And Climate
- Weather refers to the short-term, hour-to-hour and day-to-day conditions of the atmosphere.
- It changes from day-to-day and can affect people’s mood and daily activities.
- Climate is the average pattern of weather conditions and their variations over a large area for a long period, usually thirty years or more.
Elements of Weather and Climate
- Temperature, precipitation, humidity, wind, and atmospheric pressure are the main atmospheric elements that influence weather and climate.
- Their values change under different atmospheric conditions.
- Temperature: Varies daily (day and night) and seasonally as well (summer hotter than winter).
- The key factor is insolation, which is the amount of solar radiation received.
- Places farther from the equator receive less insolation.
- Asa result, temperatures are generally higher near the equator and lower near the poles.
Humidity: Humidity is the presence of water vapour in the air, forms when water evaporates from land and water bodies.
- Warm air can hold more water vapour, so humidity levels rise as temperature increases.
- High humidity makes the air feel moist and uncomfortable causing clothes to dry slowly, and sweat to evaporate less efficiently, leaving us sticky.
Precipitation: Precipitation happens when water vapour saturates a part of the atmosphere, condenses, and falls to the Earth under the force of gravity.
Forms include drizzle, rain, snow, sleet, and hail.
Influencing factors: prevailing winds, mountains, and seasons.
- Rain is the most common form, cooling the atmosphere and replenishing groundwater.
- A long absence of rainfall leads to dry climate.
Atmospheric pressure: The pressure produced by the weight of the air on Earth’s surface.
- It is highest at sea level and decreases rapidly with increasing altitude.
- Air pressure across different places depends on temperature.
- Warm air rises, forming low-pressure areas with cloudy and wet weather.
- Cold, heavy air sinks, creating high-pressure areas with clear and sunny weather.
Wind: Air moving from places with higher air pressure to places with lower air pressure.
- It may blow softly or with great force.
- Light winds can move leaves and dust, whereas strong winds during storms can uproot trees.
- Winds are named after the direction they blow from. For example, a wind blowing from the west is called a westerly.
Local winds like the sea breeze and land breeze help moderate coastal climates.
During the day, land heats faster than sea, creating a low-pressure area over land, so wind blows from sea to land (sea breeze).
At night, land cools faster than sea, creating a slight pressure difference, so wind blows from land to sea (land breeze).
Although weather conditions change frequently, the year is divided into seasons based on common weather patterns over several weeks or months.
Seasons In India
India’s climate is shaped by the tropical monsoon system, and the Indian Meteorological Department (IMD) recognises four main seasons.
Winter: India has winter from December to early April, with December and January being the coldest months (10-15°C in the northwest, 20-25°C in the southeast).
Summer or pre-monsoon: The summer or pre-monsoon lasts from April to June, sometimes July in the northwest, with inland temperatures ranging from 32-40°C and the hottest months being April in the southern regions while May in the northern region.
Monsoon or rainy (Advancing monsoon): The monsoon or rainy season lasts from June to September, dominated by the southwest monsoon winds, bringing heavy rainfall that begins in late May or early June and recedes from north India in October, while south India receives more rain during this period.
Post-monsoon (Retreating monsoon): The post-monsoon or retreating monsoon runs from October to December, with cloudless skies in the northwest India.
The Himalayan states experience spring and autumn as transitional seasons due to their temperate climate.
Traditionally, India divides the year into six seasons, each lasting about two months, based on astronomical divisions of the 12 months. These are:
- Spring (Vasanta) – March and April
- Summer (Grishma) – May and June
- Monsoon (Varsha) – July and August
- Early Autumn (Sharad) – September and October
- Late Autumn (Hemanta) – November and December
- Winter (Shishira) – January and February
Monsoon
- India’s climate is greatly influenced by the monsoon winds.
- Ancient sailors noticed the seasonal reversal of these winds and used them for navigation.
- The Arabs, who traded with India, named this phenomenon “monsoon”, from the Arabic word mausim, meaning “season.”
- Monsoon winds are seasonal winds divided into two types.
- The south-west monsoon (June-September) blows from sea to land across the Arabian Sea, Indian Ocean, and Bay of Bengal. It is caused by unequal heating of land and sea, creating low pressure over land and high pressure over the oceans, bringing moist winds and most of India’s rainfall.
- The north-east monsoon (October-February) occurs when the land cools faster than the oceans, creating high pressure over land and low pressure over the seas, with cold and dry winds blowing from land to sea.
- The north-east monsoon, after passing over the Bay of Bengal, they collect moisture and bring rain to the eastern coast of India, especially Tamil Nadu, Andhra Pradesh, and parts of Karnataka.
- The north-east monsoon is important for rainfall in the south-eastern regions of India.
- Monsoon rainfall is vital for India’s agriculture, water supply, and rural livelihoods.
- A good monsoon ensures food production, while weak monsoon can lead to droughts and excessive rainfall may cause floods. Thus, the monsoon strongly influences India’s economy, lifestyle, transportation, festivals employment and daily life.
Ancient Indians developed methods to predict rainfall for farming.
The Krishiparashara and the Brihatsamhita describe traditional techniques for forecasting rainfall.
The Krishiparashara used the positions of the Sun and the Moon, while Varahamihira used nakshatras to predict rainfall.
Many farmers in India still follow these traditional methods.
Under the National Monsoon Mission (NMM), the Ministry of Earth Sciences has developed advanced weather and climate models to improve monsoon forecasting across different time periods.
Mission Mausam initiative aims to make India “Weather Ready” and “Climate Smart” by enhancing weather observation, modelling, and forecasting standards to global levels.
These missions strengthen agriculture, disaster management, and rural development through accurate weather and climate services.
In his 5th century CE poem Meghadutam, the poet Kalidasa described the arrival of the monsoon over central India and traced the path of the monsoon clouds.
Climate Change
- Climate change refers to long-term shifts in temperature, rainfall, and wind, mainly caused by human activities like burning fossil fuels, deforestation, and industrial pollution.
- These activities increase greenhouse gases like carbon dioxide, nitrous oxide, methane and water vapour, trapping heat, and raising global temperatures, leading to floods, droughts, melting glaciers, rising seas, and biodiversity loss.
- It impacts ecosystems, human health, agriculture, and livelihoods.
- Climate change can be tackled through collective efforts such as cutting carbon footprints, using renewable energy, protecting forests and practising sustainable living.
Punjab Floods 2025: A Case Study
- Heavy monsoon rains and the rising water levels of the Satluj, Beas, and Ravi rivers led to severe flooding in Punjab in 2025.
- Large parts of the state, including farmland, villages, houses, and infrastructure, were damaged, causing severe economic, social, and environmental losses.
Causes
Natural Causes
- Western disturbances made the heavy monsoon rains in 2025 even more intense.
- The heavy rainfall affected Punjab along with Himachal Pradesh and Jammu & Kashmir.
- The Satluj, Beas, Ravi, and Ghaggar rivers were already carrying large volumes of water before the rainfall increased.
- Extra rainfall and runoff from the hills caused the rivers to overflow, leading to widespread flooding across Punjab.
Human-made Causes
Old and weak river embankments (dhusi bandh) were unable to withstand the rising water levels. Construction of houses and farms near riverbanks reduced the natural floodplain available for excess water. The build-up of silt and mud in rivers and dams lowered their capacity to store and carry water.
Late or ineffective flood warnings prevented many people from preparing in time.
These human-related factors further worsened the impact of the floods.
Effects of the Floods in Punjab
- Loss of lives and displacement of thousands into relief camps.
- Severe damage to agriculture, especially paddy crops, while poultry, and dairy farms were damaged or destroyed.
- Many animals fell ill or lost their lives.
- Destruction of roads, bridges, and public buildings.
- Spread of waterborne diseases due to stagnant water and poor sanitation.
Atmosphere and Climate Class 9 Short Notes
→ Altitude: The height of a place or object above sea level.
→ Atmosphere: The envelope of gases surrounding the Earth.
→ Atmospheric Pressure: The force exerted by the weight of air on the Earth’s surface.
→ Biodiversity: The variety of living organisms found in a particular region.
→ Carbon Dioxide: A gas present in the atmosphere that helps trap heat.
→ Carbon Footprint: Human activities such as using energy, travelling, and producing goods and services release greenhouse gases into the atmosphere.
→ Climate: The average weather conditions of a place over a long period.
→ Climate Change: Long-term changes in weather patterns caused mainly by human activities.
→ Condensation: The process by which water vapour changes into liquid water.
→ Deforestation: The large-scale removal of forests and trees.
→ Dust Particles: Tiny particles present in the air that assist in cloud formation.
→ Evaporation: The process through which water changes from liquid to vapour.
→ Exosphere: The outermost layer of the atmosphere with very thin air.
→ Global Warming: The gradual increase in the Earth’s average temperature.
→ Gravity: The force that pulls objects towards the Earth and helps keep the atmosphere around our planet.
→ Greenhouse Gases: Gases that trap heat in the atmosphere and contribute to global warming.
→ Humidity: The amount of water vapour present in the air.
→ Insolation: The amount of solar energy received by the Earth from the Sun.
→ Ionosphere: A part of the thermosphere that helps in radio communication.
→ Land Breeze: A wind that blows from the land towards the sea during the night.
→ Lunar Mansions (Nakshatras): The 27 divisions or segments of the sky used in traditional Indian astronomy and astrology to track the Moon’s movement across the heavens.
→ Mesosphere: The layer of the atmosphere where most meteors bum before reaching the Earth.
→ Monsoon: Seasonal winds that change direction with the seasons.
→ Nitrogen: The most abundant gas present in the atmosphere.
→ Oxygen: A gas essential for breathing and the survival of living organisms.
→ Ozone Layer: A layer of ozone gas in the stratosphere that absorbs harmful ultraviolet radiation.
→ Precipitation: Any form of water falling from the atmosphere to the Earth.
→ Rainfall: Water droplets falling from clouds to the Earth’s surface.
→ Renewable Energy: Energy obtained from sources that can be naturally replenished.
→ Retreating Monsoon: The period during which monsoon winds withdraw from India.
→ Sea Breeze: A cool wind that blows from the sea towards the land during the daytime.
→ South-West Monsoon: Seasonal winds that blow from the sea to the land between June and September, bringing most of India’s annual rainfall.
→ Stratosphere: The atmospheric layer that contains the protective ozone layer.
→ Sustainable Development: Development that meets present needs while conserving resources for future generations.
→ Temperature: The degree of hotness or coldness of the atmosphere.
→ Thermosphere: The layer of the atmosphere where temperatures rise sharply with height.
→ Troposphere: The lowest layer of the atmosphere where weather changes take place.
→ Water Vapour: Water present in the atmosphere in gaseous form.
→ Weather: The hour-to-hour and day-to-day condition of the atmosphere.
→ Wind: The movement of air from an area of high pressure to an area of low pressure.