Atmosphere and Climate
1. Atmosphere
- Definition: Blanket of air surrounding the Earth, held by gravity.
- Importance:
- Protects from harmful UV rays of the Sun.
- Maintains Earth’s temperature.
- Causes weather and climate.
2. Composition of Atmosphere
- Nitrogen → 78%
- Oxygen → 21%
- Other gases → Carbon dioxide (0.04%), Argon, Ozone, etc.
- Water vapour and dust particles are also present.
- Water vapour helps in cloud and rain formation.
3. Layers of Atmosphere
| Layer | Height | Key Features |
|---|---|---|
| Troposphere | 0–12 km | Weather occurs here, temperature decreases with height |
| Stratosphere | 12–50 km | Ozone layer (protects from UV), aeroplanes fly here |
| Mesosphere | 50–80 km | Meteors burn here |
| Thermosphere | 80–700 km | Auroras, radio waves reflected |
| Exosphere | Above 700 km | Very thin air, gases escape to space |
Note : Temperature decreases only in Troposphere and Mesosphere.
4. Weather and Climate
- Weather: Day-to-day condition of the atmosphere (changes quickly).
- Climate: Average weather of a place for a long time (30 years or more).
5. Elements of Weather & Climate
- Temperature: Depends on insolation (sunlight). Hotter near equator, cooler at poles.
- Humidity: Water vapour in air. High humidity makes us feel sticky.
- Precipitation: Rain, snow, hail etc. Rain is most common.
- Air Pressure: High pressure = clear sky, Low pressure = cloudy/rainy.
- Wind: Air moves from high pressure to low pressure area.
- Sea Breeze: Day (sea to land)
- Land Breeze: Night (land to sea)
6. Seasons in India
India has Tropical Monsoon Climate.
Four Seasons:
- Winter
(Dec – March): Cold in North India. - Summer
(April – June): Very hot. - Monsoon
(June – Sept): Rainy season. - Post-Monsoon
(Oct – Nov): Clearing of skies.
7. Monsoon
- Seasonal change in wind direction.
- South-West Monsoon
(June–Sept): Main rainy season. Winds come from sea to land. - North-East Monsoon
(Oct–Feb): Brings rain to Tamil Nadu and eastern coast.
Importance:
- Most important for Indian agriculture.
- Good monsoon → good crops and water.
- Bad monsoon → drought or flood.
8. Climate Change
- Long-term change in weather due to human activities.
- Causes: Burning fuels, cutting trees, pollution → increase in greenhouse gases.
- Effects: Global warming, floods, droughts, melting ice, rising sea level.
- Carbon Footprint: Amount of harmful gases released by our activities.
How to Reduce Carbon Footprint:
- Save electricity & water
- Use cycle/public transport
- Plant more trees
- Reduce plastic use
Quick Revision Points
- Most important layer → Troposphere
- Ozone layer is in → Stratosphere
- India’s climate → Tropical Monsoon
- Main source of rainfall → South-West Monsoon
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