2.4. Thermosphere

The thermosphere is located between 80 and 400 km above the mesopause. In this layer the temperature increases rapidly with increase in height. It is estimated that the temperature reaches 1500 degree C. The air is so thin that a small increase in energy can cause a large increase in temperature. Because of the thin air in the thermosphere, scientists can't measure the temperature directly. They measure the density of the air by how much drag it puts on satellites and then use the density to find the temperature.

The Earth's thermosphere also includes the region called the ionosphere. It contains electrically charged particles known as ions, and hence, it is known as ionosphere. Ionization of molecules and atoms occurs mainly as a result of ultra-violet, x-rays and gamma radiations. The high temperatures in the thermosphere also cause molecules to ionize. This is why an ionosphere and thermosphere can overlap.

Radio waves transmitted from the earth are reflected back to the earth by this layer. This layer also protects the earth from meteorites and remains of abandoned satellites. They are burned and reduced to ashes due to high temperature as they enter this layer.

Ionosphere also includes some parts of mesosphere and exosphere. Ionosphere is further divided into different layers, namely D-layer (upto 99km), E-layer (90-130km), Sporadic E-Layer, F1 & F2 layer (150-380km) and G-layer (>400km). Layers such as D-layer, E-layer, exist only during day time and vanishes as soon as sun sets.