GA Study Notes On STRUCTURE OF THE ATMOSPHERE

The Earth is surrounded by a layer of gas called the atmosphere.The atmosphere extends up to a height of about 1,600 kilometres. 

The atmosphere is composed of:
Nitrogen (78.09%),
Oxygen (20.95%),
Argon(0.93%), 
Other gases(0.03%)

Air pressure

As we go up the layers of the atmosphere, the pressure falls rapidly. The air pressure is highest at sea level and decreases with height. In areas where the temperature is high the air gets heated and rises. This creates a low-pressure area. Low pressure is associated with cloudy skies and wet weather.In areas having a lower temperature, the air is cold. It is therefore heavy. Heavy air sinks and creates a high-pressure area.High pressure is associated with clear and sunny skies.

Our atmosphere is divided into five layers starting from the earth’s surface. These are Troposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere.

1.Troposphere: This layer is the most important layer of the atmosphere. 

Its average height is 13 km.The air we breathe exists here. Almost all the weather phenomena like rainfall, fog and hailstorm occur in this layer.Tropopause - it is the layer that separates the troposphere from the stratosphere.In the troposphere, the temperature generally decreases with height, whereas above the tropopause, the temperature no longer decreases.

2.Stratosphere: Above the troposphere lies the stratosphere.

 It extends up to a height of 50 km. This layer is almost free from clouds and associated weather phenomenon, making conditions most ideal for flying aeroplanes.One important feature of the stratosphere is that it contains a layer of ozone gas, which protects us from the harmful effect of the sun rays.

Layers of the Atmosphere

3. Mesosphere: This is the third layer of the atmosphere and lies above the stratosphere.

It extends up to the height of 80 km.Meteorites burn up in this layer on entering from the space.It is the coldest layer of the atmosphere.

4.Thermosphere: In thermosphere temperature rises very rapidly with increasing height.The ionosphere is a part of this layer. This layer helps in radio transmission. 

Ionosphere: It lies immediately above the mesosphere and extends from 80 to 400 km above the Earth's surface.

The ionosphere is the part of the Earth's upper atmosphere, where ions and electrons are present to affect the propagation of radio waves.In fact, radio waves transmitted from the earth are reflected back to the earth by this layer.This layer contains electrically charged air that protects the Earth from falling meteorites as most of them burn out in this region.

5. Exosphere: The uppermost layer of the atmosphere is known as  Exosphere. This layer has very thin air. Light gases like helium and hydrogen float into space from here.