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Summary

Geography Class 21

## INTRODUCTION (5:12 PM)

- Overview & doubts related to the previous class.

## INSOLATION, HEAT BUDGET, AND ALBEDO (5:22 PM)

- The amount of incoming solar radiation is called **insolation.**
- The amount of insolation received by the Earth is 2 billionth of solar energy.
- The amount of insolation received on the surface= 1.92 calories per cm2 per minute called the **Solar Constant.**
- The incoming solar radiation is shorter in wavelength.
- This radiation is absorbed by the Earth's surface and is reemitted as **long-wavelength Terrestrial Radiation.**

## GREEN HOUSE EFFECT (5:48 PM)

- The atmosphere is transparent to incoming solar radiation and opaque to outgoing terrestrial radiation.
- The warming of the Earth's atmosphere and its surface by the absorption of terrestrial radiation by some of the gases is called the **Green House effect.**
- **The gases responsible are called Green House Gases**, for example, CO2, CH4, N2O, HFCs (Hydro-fluro carbon), PFCs (Per-fluro carbon), SF6 (Sulphur hexafluoride), Water vapor, etc.
- The Earth's surface absorbs incoming solar radiation and emits terrestrial radiation hence it acts as a source of heat for the atmosphere.
- Therefore, temperature decreases with height at the rate of 6.5 degrees celsius per km which is called **the Normal Lapse Rate.**

## HEAT TRANSFER (5:56 PM)

- **Methods of heat transfer:**
- **(1) Radiation**
- It involves the transfer of heat in the form of radiant energy.
- The incoming solar energy is in the form of electromagnetic radiation.
- **(2) Conduction**
- It involves the transfer of heat through molecular activity at the zone of contact.
- It occurs at the zone of contact between the troposphere and the Earth's surface.
- **(3) Convection**
- Transfer of heat by vertical movement of the mass of air.
- For Example, the convection of air along the equator.
- **(4) Advection**
- Transfer of heat by horizontal movement of mass.
- For Example, planetary winds and ocean currents.

## FACTORS AFFECTING INSOLATION (6:16 PM)

- **(1) Transparency of the atmosphere**
- Cloud cover, dust particles, water vapor, etc. reduces the transparency of the atmosphere and reduces insolation received at the surface.
- **(2) Latitude**
- Latitude of a place decides the angle of incidence of insolation which affects insolation received per unit area of the surface.
- **For Example,** in tropical regions insolation falls vertically and is concentrated in a small area. Along temperate and polar regions angle of incidence is oblique and insolation is distributed over a larger area.
- **(3) Length of the day**
- Longer the day, the more the insolation received at the surface. The length of the day depends on the season.

## HEAT BUDGET (6:29 PM)

- On the global scale the Earth must reradiate as much heat back to space as it receives from the sun.
- This is necessary in order to maintain a uniform temperature on the Earth.
- The gains and losses in heat by way of incoming solar radiation and outgoing terrestrial radiation are called **Heat Budget.**
- ![](https://cdn1.byjus.com/wp-content/uploads/2021/09/heat-budget-1.png)
- **Doubts related to heat budget (7:15 PM)**

## ALBEDO (7:24 PM)

- Albeo is the ratio between the reflected amount of solar radiation and the incoming solar radiation by the Earth as a whole.
- It is also called as **Reflection Coefficient.**
- The average albedo of the Earth = 35%.
- ![](https://qph.cf2.quoracdn.net/main-qimg-fa18e31f6ee35bb61858bd6fc73e7b19-pjlq)

## TEMPERATURE (7:42 PM)

- The degree of hotness or coldness of a surface is called temperature.

## Factors affecting Temperature:

- **(1) Insolation**
- Insolation in turn depends upon the transparency of the atmosphere, latitude, and length of the day.
- Even though the sun's rays are vertical along the equator throughout the year, the equator will not have maximum temperature due to cloud cover.
- **(2) Albedo**
- Surface with higher albedo reflects back more insolation resulting in less absorption of heat causing lower temperature.
- **(3) Nature of the surface**
- Earth behaves differently depending upon the specific heat of the surface.
- The land surface with lower specific heat, heats up more rapidly and intensely than the water surface.
- Also, the land cools rapidly.
- **(4) Distance from the sea or continentality**
- The locations that are in the interior of the continent experience a higher range of temperatures than coastal locations.
- For Example, Delhi experiences hotter summers and colder winters than Mumbai.
- **(5) Distribution of continents**
- Northern Hemisphere with more proportion of land than oceans experience a higher range of temperature than the Southern Hemisphere with more water surface.
- **(6) Altitude**
- Temperature decreases with an increase in altitude.
- **(7) Winds**
- Air in motion is called Winds.
- They transport temperatures prevailing in one area to another.
- For Example, planetary winds.
- **(8) Ocean currents**
- Ocean currents are like rivers inside the oceans.
- They transport warm water from the tropics to polar regions and vice versa helping in the global distribution of temperatures.

## TOPIC FOR THE NEXT CLASS: DISTRIBUTION OF TEMPERATURE ACROSS THE GLOBE