Background :-

The atmosphere is comprised of layers based on temperature. These layers are the troposphere, stratosphere, mesosphere and thermosphere. A further region at about 500 km above the Earth’s surface is called the exosphere.
Layers of atmosphere :-

Troposphere:-

1. This is the lowest part of the atmosphere that is the part we live in. It contains most of the weather – clouds, rain, snow. In this part of the atmosphere the temperature gets colder as the distance above the earth increases, by about 6.5°C per kilometre. The actual change of temperature with height varies from day to day, depending on the weather.
2. The troposphere contains about 75% of all of the air in the atmosphere, and almost all of the water vapour (which forms clouds and rain). The decrease in temperature with height is a result of the decreasing pressure
3. The lowest part of the troposphere is called the boundary layer. This is where the air motion is determined by the properties of the Earth’s surface.
4. The top of the troposphere is called the tropopause. This is lowest at the poles, where it is about 7 – 10 km above the Earth’s surface. It is highest (about 17 – 18 km) near the equator.

The Stratosphere

1. This extends upwards from the tropopause to about 50 km. It contains much of the ozone in the atmosphere. The increase in temperature with height occurs because of absorption of ultraviolet (UV) radiation from the sun by this ozone. Temperatures in the stratosphere are highest over the summer pole, and lowest over the winter pole.
2. By absorbing dangerous UV radiation, the ozone in the stratosphere protects us from skin cancer and other health damage.

The Mesosphere
The region above the stratosphere is called the mesosphere. Here the temperature again decreases with height, reaching a minimum of about -90°C at the “mesopause”

The Thermosphere and Ionosphere

1. The thermosphere lies above the mesopause, and is a region in which temperatures again increase with height. This temperature increase is caused by the absorption of energetic ultraviolet and X-Ray radiation from the sun.
2. The region of the atmosphere above about 80 km is also caused the “ionosphere”, since the energetic solar radiation knocks electrons off molecules and atoms, turning them into “ions” with a positive charge. The temperature of the thermosphere varies between night and day and between the seasons, as do the numbers of ions and electrons which are presen

The Exosphere
The region above about 500 km is called the exosphere. It contains mainly oxygen and hydrogen atoms, but there are so few of them that they rarely collide – they follow “ballistic” trajectories under the influence of gravity, and some of them escape right out into space.