Geography Class 20

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)

• 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)

Summary Index for Geography Class 20

1. Review of Previous Class (05:12 PM)

   • Questions on topics covered in the previous class.

2. Climatology Overview (05:21 PM)

   • Definitions and distinctions between atmosphere, weather, and climate.

3. Composition of Atmosphere (05:45 PM)

   • Detailed breakdown of atmospheric components:
     • Nitrogen: Role in soil and plant absorption.
     • Oxygen: Importance in respiration and photosynthesis.
     • Carbon Dioxide: Greenhouse gas role.
     • Noble Gases: Non-reactive gases.
     • Water Vapour: Variability and role in weather phenomena.
     • Dust Particles: Role in cloud formation.
     • Hygroscopic Nuclei: Importance in condensation.

4. Structure of the Atmosphere (06:20 PM)

   • Homosphere vs. Heterosphere:
     • Differences in gas mixing, presence of water vapour and dust particles, and molecular vs. atomic gas forms.
   • Layers within these spheres:
     • Homosphere: Troposphere, Stratosphere, Mesosphere.
     • Heterosphere: Thermosphere, Ionosphere.

5. Troposphere (06:47 PM)

   • Extent, characteristics, and significance in weather phenomena.
   • Explanation of the Normal Lapse Rate and the Tropopause.

6. Stratosphere (07:14 PM)

   • Characteristics, temperature changes, and the presence of stratospheric clouds.
   • Transition to the Stratopause.

7. Mesosphere (No time mentioned)

   • Extent, temperature decline, and transition to Mesopause.

8. Thermosphere (07:43 PM)

   • Characteristics, temperature rise, and layer composition.

9. Exosphere (No time mentioned)

   • Composition and presence of the magnetosphere.
   • Van-Allen Radiation Belts.

10. Ionosphere (No time mentioned)

    • Formation due to ionization, layers, and significance in radio communication.

11. Karman Line (No time mentioned)

    • Definition as the boundary of outer space and its significance.

12. Next Class Topic (No time mentioned)

• Preview of the next topic: Insolation and Heat Budget.