Teachers recommend using Class 9 SST Notes and NCERT Class 9 SST Chapter 3 Atmosphere and Climate Notes for quick revision before tests.
Class 9 Atmosphere and Climate Notes
Class 9 SST Chapter 3 Atmosphere and Climate Notes
Structure and Composition; Elements of Weather and Climate, Seasons in India
Introduction
The domain of air that surrounds the earth is called the atmosphere. It is a layer of gases. These layers are like an onion – each has different temperature behaviour, density and roles in protecting life and enabling weather. It provides us with oxygen for breathing and protects us from the harmful ultraviolet (UV) rays of the sun. It also traps heat to keep the Earth’s temperature moderate.
Composition of the atmosphere
Air is a mixture of many gases (nitrogen —78%, oxygen —21%, argon —0.9%, carbon dioxide —0.04%) along with tiny dust particles and variable water vapour.
Nitrogen is the most abundant gas and is inhaled and exhaled by humans and animals without being used directly, but soil bacteria fix it into forms that plants can absorb for growth.
Oxygen is the second most plentiful gas. It is essential for respiration in humans and animals. Green plants release oxygen during photosynthesis. This helps maintain a natural balance in the atmosphere.
Carbon dioxide, though present in very small amounts (—0.04%), is vital for photosynthesis in plants; the balance between plants using C02 and animals releasing it is disturbed by large-scale burning of coal, oil and other fuels.
Other gases like argon, helium, ozone and hydrogen exist in trace quantities, while tiny dust particles are always present in the air and play roles in weather processes such as cloud formation.
Class 9 SST Chapter 3 Notes – Atmosphere and Climate Notes Class 9
Structure of the atmosphere
The atmosphere is divided into layers based mainly on how temperature changes with height. From the surface upward. The layers of the atmosphere are:
1. Troposphere:
- Average height of about 12 kilometres.
- All weather phenomena (clouds, rain, storm) and the air we breathe exist here.
- Temperature decreases with increasing height. Ends at the tropopause.
2. Stratosphere:
- Avg. height – 50 km.
- It is free from all weather conditions.
Thus, ideal for flying aeroplanes.
- It contains the Ozone layer, which protects us from the harmful UV rays.
- Ends at the stratopause.
3. Mesosphere:
- Avg. height – 80-85 km.
- Meteorites burn up here once they enter the atmosphere.
- Ends at the mesopause.
4. Thermosphere:
- The thermosphere extends from 80 to 700 km.
- Temperature increases rapidly with increasing height.
- Contains the ionosphere. This is a layer of ionised gas and helps in transmitting radio waves and causes aurora in the polar regions.
- Space stations orbit here.
5. Exosphere:
- Uppermost layer, above —700 km, gradually merges into outer space.
- It is the extremely thin layer.
- Merges into outer space.
- Gravitational force of the earth becomes so weak that atoms easily escape (e.g., hydrogen and helium)
Weather and Climate
Weather: It refers to the atmospheric conditions prevailing over a shorter period of time and over a smaller geographical area.
Climate: It refers to the average weather condition of a sizeable area of the Earth’s surface for a long period of time, usually spread over a span of at least 30-35 years, and is called Climate.
Difference between weather and climate
| Weather | Climate |
| Weather deals with atmospheric conditions extending over a shorter period of time. | Climate gives an integrated picture of weather conditions extending over a longer period of time such as a season or a year. |
| Weather is always changing. For example, cloudy weather may change to clear. | Climate changes at a slow pace. |
| Weather refers to a particular place. | Climate refers to the atmospheric conditions extending over a large area. |
| Weather data are based on actual observation. | Climate data gives an average of the weather conditions collected during a month, season or year. |
1. Elements of Weather and Climate
The major elements that influence weather and climate are temperature, humidity, precipitation, atmospheric pressure, and wind, and these elements affect human life on Earth.
2. Temperature
Temperature varies between day and night as well as across different seasons, with summers generally being hotter than winters.
Insolation is the incoming solar energy received by the Earth and is an important factor affecting temperature distribution.
Since insolation decreases from the Equator towards the poles, temperature also decreases from the Equator towards the poles.
3. Humidity
Humidity refers to the presence of water vapour or moisture in the air, which is formed when water evaporates from land and water bodies.
Warm air can hold more water vapour, so higher temperatures lead to higher humidity levels.
High humidity makes clothes dry slowly and causes sweat to evaporate more slowly, making people feel uncomfortable.
4. Precipitation
Precipitation occurs when water vapour in the atmosphere condenses and falls to the Earth due to gravity in the form of drizzle, rain, snow, sleet, or hail.
Prevailing winds, mountains, and seasons are the main factors that influence precipitation.
Rain is the most common form of precipitation, helps lower the temperature of a place, and is the main source of groundwater.
A long absence of rainfall results in a dry climate.
5. Atmospheric Pressure
Atmospheric pressure is the pressure exerted by the weight of air on the Earth’s surface, and it decreases with increasing altitude.
High temperatures cause air to rise and create low- pressure areas, which are associated with cloudy and wet weather.
Low temperatures cause air to sink and create high- pressure areas, which are associated with clear and sunny weather.
Air always moves from high-pressure areas to low- pressure areas.
6. Wind
Wind is the movement of air from high-pressure areas to low-pressure areas, and it can range from gentle breezes to powerful storms.
Seasons in India
1. Climate of India
India has a tropical monsoon climate, and the India ‘ Meteorological Department (IMD) recognises four . distinct seasons in the country.
2. Winter Season (December to Early April)
- The winter season lasts from December to early April, with December and January being the coldest months.
- The average temperature in north-western India is around 10-15°C, while temperatures increase towards the Equator and reach about 20-25°C in south-eastern India.
3. Summer or Pre-Monsoon Season (April to June/July)
- The summer or pre-monsoon season extends from April to June or up to July in north-western India.
- April is the hottest month in western and southern India, whereas May is the hottest month in northern India, with average temperatures in most inland regions remaining above 32-40°C.
4. Monsoon or Rainy Season (Advancing Monsoon) (June to September)
- The monsoon season lasts from June to September and is dominated by the humid south-west monsoon winds, which spread across the country in late May or early June.
- Monsoon rains begin to retreat from northern India in October, while southern India receives significant rainfall during this period.
5. Post-Monsoon Season (Retreating Monsoon) (October to December)
- The post-monsoon or retreating monsoon season extends from October to December, and October and November are generally cloudless in north-western India.
6. Additional Seasons in the Himalayan Region
Due to their temperate climate, the Himalayan states experience two additional seasons, namely spring and autumn.
Monsoon in India
The word monsoon has come from the Arabic word ‘Mausim’ meaning season. The monsoon is experienced roughly between 20°N and 20°S latitudes, in the tropical belt.
Monsoon is the rain bearing wind which reverses its direction with the change of’mausim’ or season and blows throughout the Indian subcontinent, especially during the summer season.
Monsoons are seasonal winds that may sometimes be associated with heavy rainfall, thunderstorms and strong winds.
It accounts for most of the rainfall received by India.
Rainfall is neither continuous nor regular/ not evenly distributed.
Strength of rainfall depends on the intensity and frequency of depressions in the Bay of Bengal.
Onset of monsoon – 1st June.
Mechanism of Indian Monsoon
The Sun causes differential heating and cooling of land and water. This creates low pressure on the landmass of India and high pressure over the ocean surface.
The Inter Tropical Convergence Zone (ITCZ) is normally positioned about 5°N of the equator. It shifts over the Ganga plains during summer. It is also known ds the monsoon trough during the monsoon season.
The high pressure area, east of Madagascar is approximately 20°S over the Indian Ocean and largely affects the Indian Monsoon.
The Tibetan plateau gets intensely heated during summer. This results in strong vertical air currents and formation of low pressure over the plateau.
The westerly jet stream moves to the north of the Himalayas and the tropical easterly jet stream moves over the Indian Peninsula during summer.
The periodic change in pressure conditions between the Pacific Ocean and the Indian Ocean that is known as the Southern Oscillation or SO also affects the monsoon.
Annual rainfall zones of India
| Rainfall Zone (cm) | Major Areas/Regions |
| Above 400 cm | Western slopes of Western Ghats (Kerala-Karnataka coast), parts of Meghalaya (Mawsynram- Cherrapunji region), Andaman & Nicobar Islands |
| 200-400 cm | Northeastern states (Assam, Arunacljal Pradesh, Meghalaya, Nagaland, Manipur, Mizoram, Tripura), Konkan-Malabar Coast |
| 100-200 cm | Eastern India, Odisha, West Bengal, Bihar/Jharkhand, Chhattisgarh, eastern Madhya Pradesh, parts of Andhra Pradesh and Tamil Nadu |
| 60-100 cm | Central India, interior Maharashtra, Telangana, Karnataka Plateau, Uttar Pradesh, Haryana, Punjab |
| 40-60 cm | Western Madhya Pradesh, Rajasthan (eastern parts), Gujarat, rain-shadow regions of Deccan Plateau |
| 20-40 cm | Western Rajasthan, Kutch region of Gujarat, Ladakh and cold desert regions |
| 0-20 cm | Extreme western Rajasthan (Thar Desert), parts of Ladakh |
Differentiate between SW and NE Monsoon
| SW Monsoon | NE Monsoon |
| They blow from SW to NE from June to September. | They blow from NE to SW in the months of October to February. |
| These are onshore humid winds because they blow from sea to land. | These are offshore dry winds because they blow from land to sea. |
| These are warm winds as they come from lower latitudes near the equator. | These are cool winds. |
| These warm and humid winds cause widespread rainfall. | These cold and dry offshore winds give no rains to India except on the Coromandel Coast. |
| These winds are known for their uncertainties. | They do not suffer from uncertainties. |
Impacts of Monsoon on India
The monsoon plays a crucial role in shaping India’s climate, agriculture, economy and daily life. Since most of India’s rainfall is received during the monsoon season, its performance directly affects the country’s development and well-being.
Impact on Agriculture
India is basically an agrarian economy and is largely dependent on the monsoon. A timely and adequate monsoon ensures good crop production, while a weak or delayed monsoon leads to crop failure and drought conditions.
- The sowing of kharif crops like – rice, maize, cotton and sugarcane depends on the arrival of monsoon rains.
- Adequate rainfall helps maintain soil moisture and groundwater levels necessary for irrigation.
- Excessive rainfall, however, may cause waterlogging and crop damage.
- Failure of the monsoon can result in drought, reduced agricultural output and food shortages.
Impact on Economy and Livelihoods
Especially the rural livelihood of the Indian economy is closely linked to the monsoon.
- A good monsoon shower leads to higher agricultural production thereby increasing the farmer’s income significantly and also supports the agro-based industries.
- Poor monsoon conditions reduce crop yields, affecting rural employment and increasing economic instability.
- Hydroelectric power generation also depends on sufficient monsoon rainfall, which affects electricity supply and industrial productivity.
Impact on Daily Life and Society
The monsoon has a strong influence on the daily lives of people in India.
- Monsoon rains provide relief from the intense summer heat and replenish water resources such as rivers, lakes and reservoirs.
- However, heavy rainfall can cause floods, landslides, traffic disruptions and damage to houses and infrastruc-ture.
- Urban areas often face waterlogging and sanitation issues during heavy monsoon rains.
- The arrival and withdrawal of the monsoon also influence festivals, travel and daily routines of people.
National Monsoon Mission and Mission Mausam
The National Monsoon Mission (NMM), launched by the Ministry of Earth Sciences, Government of India, has developed advanced weather and climate prediction models to improve monsoon forecasting across different time scales.
Mission Mausam aims to make India a “Weather- Ready” and “Climate-Smart” nation by improving weather and climate services. It focuses on providing timely and accurate observations, modelling, and forecasts to support sectors such as agriculture, disaster management, and rural development.
Climate Change, Carbon Footprints and Flood
1. Climate Change
Climate change is one of the most urgent challenges facing the Earth and refers to long-term changes in weather patterns such as temperature, rainfall, and wind, mainly caused by human activities like burning fossil fuels, deforestation, and industrial pollution.
Human activities increase greenhouse gases such as carbon dioxide, methane, nitrous oxide, and water vapour, which trap heat in the atmosphere and raise global temperatures.
Climate change causes more frequent floods, droughts, melting glaciers, rising sea levels, and loss of biodiversity, affecting ecosystems, human health, agriculture, and livelihoods.
Its impacts are felt by all sections of society, especially women and children.
Carbon footprints
Reducing carbon footprints, using renewable energy, protecting forests, and adopting sustainable lifestyles can help combat climate change, and every individual can contribute towards a greener future.
A carbon footprint is the total amount of greenhouse gases released into the atmosphere as a result of human activities such as transportation, energy use, and the production of goods and services.
Walking, cycling, using public transport, saving electricity and water, and reusing and recycling materials are effective ways to reduce one’s carbon footprint.
Case Study: Punjab Floods, 2025
In 2025, Punjab experienced severe floods due to heavy monsoon rains and the swelling of the Satluj, Beas, and Ravi rivers, causing widespread damage to villages, farmlands, houses, roads, and bridges.
Heavy monsoon rainfall, intensified by western disturbances, caused rivers to overflow, while weak embankments, encroachment near riverbanks, silt accumulation, and delayed flood warnings further increased the severity of the floods.
The floods led to loss of lives, displacement of thousands of people, destruction of crops and livestock)’ damage to infrastructure, and the spread of water-borne diseases and sanitation problems.