The structure of the atmosphere is highly complex. The atmosphere consists of different layers with varying densities and temperatures.

● The temperature changes irregularly with height. Density is highest near the surface of the earth and decreases with increasing altitude.

● The column of the atmosphere is divided into five different layers depending upon the temperature condition. They are:

1. Troposphere

2. Stratosphere

3. Mesosphere

4. Thermosphere

5. Exosphere.

Troposphere

● The troposphere is the lowermost layer of the atmosphere which immediately overlies the earth’s Surface.

● The air we breathe exists here.

● This layer contains dust particles and water vapour. Almost all the weather phenomena like rainfall, fog and hailstorm occur in this layer.

● The troposphere is the important layer since it is the locale of all the vital atmospheric processes which create the climatic and weather conditions on the earth’s surface.

● The troposphere is the densest part of the atmosphere.

● Its average height is 13 km and extends roughly to a height of 8 km near the poles and about 18 km at the equator.

● The thickness of the troposphere is greatest at the equator because heat is transported to great heights by strong convection currents.

● The troposphere at any latitude is thicker in summer than in winter.

● The temperature in this layer decreases at the rate of 1°C for every 165m of height. This is called Normal Lapse Rate. This is the most important layer for all biological activity.

● in the lower part of the troposphere, the lapse rate along the vertical is very steep.

● Innumerable vertical currents moving throughout the year cause the troposphere to remain unstable.

● This instability leads to upward movement, condensation, formation of clouds and precipitation.

● The transition separating the troposphere from the stratosphere is termed tropopause.

Stratosphere

● The stratosphere is found above the tropopause and extends up to a height of 50 km.

● One important feature of the stratosphere is that it contains the ozone layer.

● The lower portion of the stratosphere has a maximum concentration of ozone is called Ozonosphere. It is found in between the height of 15 km to 35 km above sea level.

● This layer absorbs ultraviolet radiation and shields life on the earth from intense, harmful forms of energy. Therefore, temperature rises in this layer.

● This layer is free from atmospheric disturbance, making conditions most ideal for flying aero planes.

● This layer is also almost free from clouds and associated weather phenomena.

● The transition separating the stratosphere from the mesosphere is termed stratopause.

Mesosphere

● This is the third layer of the atmosphere.

● The mesosphere lies above the stratosphere, which extends up to a height of 80 km.

● Meteorites burn up in this layer on entering from space.

● In this layer, the temperature starts decreasing with the increase in altitude and reaches up to minus 100°C at the height of 80 km.

● The upper limit of the mesosphere is known as mesopause.

Thermosphere

● In the thermosphere, the temperature rises very rapidly with increasing height.

● The ionosphere is a part of this layer.

Ionosphere

● The ionosphere is located between 80 and 400 km above the mesopause.

● Since the layer contains electrically charged particles called ions, it is known as the ionosphere.

● Radio waves transmitted from the earth are reflected in the earth by this layer.

● The temperature here starts increasing with height.

(a) D Layer (between the height of 60 km to 90 km): It reflects the signals of low-frequency radio waves but absorbs the signals of medium and high frequency. This layer disappears with the sunset.

(b) E Layer (between the height of 99 km to 130 km): It is also known as the Kennelly-Heaviside layer. This layer reflects the medium and high-frequency radio waves back to Earth.

(c) F layer (at the height of 250 km): It reflects back high-frequency radiowaves. The phenomenon of Aurora generated in this layer is called Aurora Borealis in the North Pole and Aurora Australis in the South Pole.