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Summary

Geography Class 20

## Questions on topics taught in the previous class (05:12 PM)

## Climatology (05:21 PM)

- **Atmosphere:**The gaseous envelope which **surrounds the earth** from all sides and is attached to the earth's surface by gravitational force.
- **Weather:** It is the day-to-day state of the atmosphere.
- **Climate:**The average atmospheric conditions of an area over a considerable period of time calculated for a **minimum of 30 years**.

## Composition of Atmosphere (05:45 PM)

![](https://lotusarise.com/wp-content/uploads/2020/03/gases-in-atmosphere-Composition-of-Atmosphere.jpg)

- **Nitrogen:** The atmospheric nitrogen gets converted into soil nitrogen through **nitrogen fixation**.
- Plants are capable of absorbing it from the soil.
- **Oxygen:**Oxygen is **chemically active**. Oxygen is taken directly through respiration.
- It is consumed at the **cellular level**.
- Oxygen is released into the atmosphere through the process of photosynthesis by plants.
- **Carbon dioxide:** It is released by both plants and animals and consumed by plants only i.e. during Photosynthesis.
- It is called **Greenhouse Gas**.
- It helps in maintaining a stable temperature in the atmosphere.
- **Noble Gases:** These gases are **non-reactive** in nature.
- **Water vapour:** It is the most **variable gas** in the atmosphere. It is responsible for all weather phenomena in the atmosphere.
- It is a **greenhouse gas** capable of absorbing Heat.
- 99 per cent of water vapour is concentrated in the lower 16 km of the atmosphere.
- **Dust Particles:** It is concentrated in the lower levels of the atmosphere.
- It acts as **hygroscopic nuclei** and helps in condensation and cloud formation.
- It is released into the atmosphere through weathering, erosion, and from Volcanic Eruptions.

|  |
| --- |
| Hygroscopic Nuclei:Hygroscopic means something which attracts water. Hygroscopic Nuclei are microscopic particles that allow water vapours to condense on their surfaces. |

## Structure of Atmosphere (06:20 PM)

|  |  |
| --- | --- |
| Homosphere | Heterosphere |
| It is a layer with uniform mixing of gases. | In this layer, gases form different layers. |
| It is up to 80 km. | It is beyond 80 km. |
| It contains water vapour and dust particles. | It contains the minimum amount of water vapour and dust particles. |
| In this layer, gases are in molecular form. | In this layer, gases are in atomic form. |
| It consists of three layers: troposphere; Mesosphere and Stratosphere. | It consists of two layers: Thermosphere and Ionosphere. |

## Troposphere (06:47 PM)

- It extends from sea level **to 16 kilometres** in the tropics and 6 kilometres in the poles.
- It is a **zone of turbulence** and convection due to the continuous mixing of gases.
- All weather phenomenon is restricted to Troposphere due to the presence of water vapour and dust particles.
- Temperature decreases from sea level **at 6.5 degrees Celsius per kilometre, called** the Normal Lapse Rate.
- The edge of the troposphere is called the **tropopause**, which is a transition zone to the stratosphere.

## Stratosphere (07:14 PM)

- It extends from Tropopause to **50 Kilometres.**
- It is called so because the layers are **stratified** and **non-convective** in nature.
- The temperature rises in the stratosphere due to the **absorption of UV rays by Ozone** in this layer.
- The conditions are **extremely dry** except for some rare clouds called stratospheric clouds. Example: Mother of Pearl.
- The top of the stratosphere is called **Stratopause**.

## Mesosphere

- It extends from stratopause to **80 km.**
- **Temperature decreases** with height and reaches its lowest in the atmosphere.
- The top of the mesosphere is called Mesopause.

## Thermosphere (07:43 PM)

- It extends from **80 km to 500-700 km.**
- It consists of a lower Nitrogen layer and upper oxygen layer.
- The temperature rises rapidly due to the absorption of high-energy solar radiation.
- Temperature reaching up to **1200 degree celsius** at 350 km.

## Exosphere

- It extends from the edge of **the thermosphere to the vacuum.**
- It contains atomic Oxygen, Helium, and Hydrogen.
- It contains a **magnetosphere** composed of electrons and Protons derived from Solar Winds and charged particles.
- They have been arranged in two bands at 3000 km and 16000 km which are called as **Van-Allen Radiation Belts.**

## Ionosphere

- It exists between **80 to 650 km** within the thermosphere.
- It is formed due to **ionization by solar radiation**. It is made up of multiple layers D, E, F, G, etc
- Ionosphere reflects **short-wave radio waves** helping in radio communication.

## Karman Line

- It is the boundary where outer space begins. It is at **an altitude of 100 km** from sea level.
- International law does not define the limit of air space. It is a line agreed upon for aircraft navigation through consensus.
- Above, this line of **air is too thin** for any aircraft balloon or any other flight, other than spacecraft.

## (Next Class: Insolation, Heat Budget)