🔷 1. Insolation
Meaning:
The energy received by the Earth from the Sun is called Insolation.
It reaches the Earth in the form of electromagnetic waves, which include visible light, ultraviolet (UV), and infrared (IR) rays.
Importance:
- Insolation controls the climate, temperature, and weather of the Earth.
- Without solar energy, life and weather systems could not exist.
🔷 2. Solar Constant
- The average amount of solar energy received on a unit area at the top of the atmosphere, when the Earth is at its mean distance from the Sun.
- Its value is about 2 calories per cm² per minute.
- It represents the constant rate at which solar energy reaches the Earth’s outer atmosphere.
🔷 3. Factors Affecting Insolation
- ☀️ Angle of the Sun’s Rays:
- When the Sun is overhead, the rays are vertical → more heating.
- When the Sun is slanting, the rays spread over a larger area → less heating.
- ⏰ Duration of the Day:
- Longer days → more insolation.
- Shorter days → less insolation.
- 🏔 Altitude:
- Temperature decreases with height (about 1°C for every 165 m rise).
- 🌫 Cloud Cover:
- Clouds reflect and absorb sunlight, reducing the amount reaching the surface.
- 🌍 Nature of the Surface:
- Dark surfaces absorb more heat, while light-colored surfaces reflect more.
🔷 4. Earth’s Energy Balance
The Earth’s Heat Balance refers to the balance between the incoming solar radiation and the outgoing terrestrial radiation.
Energy Distribution:
📊 Result:
Incoming energy = Outgoing energy → Earth’s average temperature remains stable 🌏
🔷 5. Heating and Cooling of the Atmosphere
The atmosphere is not directly heated by the Sun.
It is mainly heated by the Earth’s surface, which absorbs solar energy and then re-emits it as heat.
Modes of Heat Transfer:
- 🔥 Conduction:
- Transfer of heat from the Earth’s warm surface to the lower layers of air.
- 🌡 Convection:
- Warm air rises, cool air sinks — creating vertical movement of heat.
- 💨 Advection:
- Horizontal transfer of heat through wind (e.g., warm or cold air movement).
- ☀️ Radiation:
- The Earth re-radiates absorbed energy as long-wave infrared radiation.
🔷 6. Terrestrial Radiation
- The Earth absorbs short-wave solar energy and emits long-wave infrared radiation back to the atmosphere.
- This outgoing energy helps maintain the Earth’s temperature balance.
🌿 Greenhouse Effect:
- Certain gases like CO₂, CH₄, O₃, and water vapour trap the outgoing heat and prevent it from escaping into space.
- This natural process keeps the Earth’s average temperature around 15°C.
- Without greenhouse gases, the temperature would drop to about −18°C.
✅ Note: The Greenhouse Effect is essential for maintaining life on Earth.
🔷 7. Heat Budget of the Earth
Definition:
The heat budget is the balance between the total incoming solar radiation and the total outgoing terrestrial radiation.
✅ Conclusion:
The Earth emits as much energy as it receives → maintaining a heat equilibrium.
🔷 8. Temperature
- Temperature refers to the degree of hotness or coldness of a body or place.
- It is measured with a thermometer.
- Common units: Celsius (°C), Fahrenheit (°F), and Kelvin (K).
🔷 9. Factors Controlling Temperature
- 🌐 Latitude:
- Temperature decreases from the equator to the poles.
- 🏔 Altitude:
- Higher altitudes have lower temperatures.
- 🌊 Distance from the Sea:
- Coastal areas have moderate temperatures.
- Interior areas experience greater variations (continental effect).
- 🌊 Ocean Currents:
- Warm currents raise temperatures of coastal regions.
- Cold currents lower temperatures.
- ☁️ Cloud Cover:
- Clouds reduce solar heating during the day and trap heat at night.
- 🌍 Nature of Surface:
- Land heats and cools faster than water, affecting local temperature patterns.
🔷 10. Temperature Inversion
Normally, temperature decreases with height.
But sometimes, the reverse happens — temperature increases with height.
This condition is called Temperature Inversion.
Causes:
- Clear, calm, and cold nights 🌌
- Cold air trapped below warm air 🌫
- Valley regions where cold air settles at the bottom 🏞
📍 Result:
Lower layers become colder than upper layers → frost and fog often occur.
🔷 11. Distribution of Temperature
Temperature is unevenly distributed across the Earth due to various physical and geographical factors.
Isotherms:
- Lines on a map joining places with the same temperature.
Global Patterns:
- Equatorial region → hottest
- Polar regions → coldest
- Northern Hemisphere → higher temperature variation (more land)
- Southern Hemisphere → moderate variation (more ocean)
