Class 11 Geography chapter 7 composition and structure of atmosphere notes

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Composition and structure of atmosphere 

Intro 

•  99% of total mass of the atmosphere is confined in the height of 32 km from the surface of Earth 
• The proportion of gases changes in the higher layers of the atmosphere in such a way that Oxygen will be almost in negligible quantity at the height of 120 km 
• Carbon dioxide and water vapour are found only up to 90 km from the surface of Earth

Carbon dioxide 

• It is transparent to incoming solar radiation but Opaque to outgoing terrestrial radiation this means that because of this gas the heat couldn’t go out the retaining the warm of planet
• It absorbs a part of terrestrial radiations and reflect back some part of it towards the surface of Earth

Green house effect 

• The volume of other gases on the planet does not increase in few years but the volume of carbon dioxide has been rising at an alarming rate in the past few years 
• This leads to an increase in temperature .
• This also led to greenhouse effect.

Ozone 

• Ozone is another important component of atmosphere which is found between 10 to 50 km about the surface of Earth 
• It acts as a filter and absorbs ultraviolet rays of the sun so that they couldn’t enter Earth and harm us 
• Due to the present greenhouse effect the ozone layer is depleting

Water vapour 

• Water vapour decreases with increase in altitude 
• In warm areas the level of water vapour is higher while in cold areas it may be less 
• Water vapour also decreases from the equator towards the pole 
• It absorbs parts of the isolation from the sun and the heat of the planet 
• Thus it acts like a blanket which neither allows Earth to become too hot nor too cold 

Dust particles 

• Dust particles are generally found in lower layers of atmosphere but conventional air current can take them to higher levels as well 
• The higher concentration of dust particles is found in subtropical and temperate regions due to dry winds
• Dust and salt particles act as hygroscopic nuclei around which water vapour condenses to produce clouds 

Structure of atmosphere 

1. Troposphere

• Height:
• Extends up to about 8-15 km above sea level, with variations based on latitude (thicker at the equator, greater conventional current transport air at higher levels, thinner at the poles).
• Characteristics:
• This is the lowest layer of the atmosphere, where almost all weather phenomena, such as clouds, rain, and storms, occur.
• Contains about 75% of the Earth’s atmosphere by mass.
• The air is densest in this layer, which leads to a gradual decrease in temperature with altitude (about 1°C for every 165 m)
• Contains water vapour, dust particles, and other gases that are important for weather patterns.
• Key Events:
• Cloud formation, weather phenomena, and airplanes typically fly in the lower and middle parts of this layer.
• Tropopause 
• The temperature is about minus 80 degree Celsius over the equator and about minus 45 degree Celsius the temperature here is nearly constant

2. Stratosphere

• Height:
• Extends from about 15 km to 50 km above Earth’s surface.
• Characteristics:
• This layer contains the ozone layer (around 20-30 km), which absorbs and scatters ultraviolet (UV) radiation from the Sun, providing protection to life on Earth.
• In contrast to the troposphere, temperature increases with altitude in this layer (due to the absorption of UV radiation by the ozone).
• Air is thin and stable, with very little weather activity.
• Key Events:
• Commercial jet aircraft usually fly in the lower stratosphere (above the troposphere), where air is more stable and has less turbulence

3. Mesosphere

• Height:
• Extends from about 50 km to 85 km above Earth’s surface.
• Characteristics:
• In this layer, temperature decreases with altitude, and it is the coldest layer of the atmosphere. Temperatures can drop to -100°C at the top of the mesosphere.
• This layer is where most meteors burn up upon entering Earth’s atmosphere, due to the high density of air molecules at this height.
• Key Events:
• Meteor showers are observed in this layer as meteoroids from space burn up

4. Thermosphere

• Height:
• Extends from about 85 km to 500 km above Earth’s surface
• Characteristics:
• The ionosphere (a region of charged particles) is found in the lower part of the thermosphere. This layer reflects radio waves and helps in long-distance 
• location of ionosphere – between 80 to 400 km above mesopause 
• Auroras (northern and southern lights) occur in this layer due to solar wind interactions with Earth’s magnetic field.
• Key Events:
• Spacecraft and satellites orbit Earth in this layer. The ionosphere also plays a crucial role in radio wave transmission.

5. Exosphere

• Height:
• Extends from about 500 km to 10,000 km above Earth’s surface.
• Characteristics:
• The exosphere is the outermost layer of Earth’s atmosphere, where atmospheric particles are extremely sparse.
• Here, particles are so far apart that they can travel long distances without colliding.
• This layer is where Earth’s atmosphere transitions into space.
• Key Events:
• Satellites orbit in this layer, and spacecraft that are leaving Earth’s atmosphere pass through this region on their way to outer space.

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