Reflecting the parameters of the earth’s atmosphere, the general assumption is, ‘as the altitude increases, the temperature decreases’. However, there is an exception to this phenomenon. If we consider the layers of atmosphere like Troposphere, Stratosphere and Mesosphere, it gets cooler as we go higher. However, it is in the Thermosphere that we find the temperature inversion. Here, the temperature increases with height. The fourth layer, Thermosphere, is above the Mesosphere and below the Exosphere. The air in the layer is so thin that scientists find it difficult to measure its temperature. Hence, in order to ensure accuracy, they first measure the density of air by measuring the drag on the satellites and use them to determine the temperature.

Where is Thermosphere situated?

As discussed earlier, in the earth’s atmosphere, Thermosphere is a region of increasing temperature. Located above the Mesosphere, its base is known as the mesopause and the part at its top is known as thermopause. The former is located at an altitude of about 80 km whereas the latter at approximately 450 km. the upper atmosphere is together formed by the Thermosphere and the Exosphere. Compared to all the other four atmospheric temperature-defined layers, the Thermosphere begins at about 90 km above earth, which is the highest above the earth’s surface and reaches to a height of about 500 km. As also, it extends from about 90 km to anywhere between 500 km–1,000 km above our planet. It extends vertically for a distance of about 402km–885 km and this makes it the biggest layer of the earth’s atmosphere. 

How did ‘Thermosphere’ derive its name?

Air in the Thermosphere is warm as the oxygen molecules absorb the energy from the sun’s rays. In addition, the temperature increases with altitude and reaches higher than 1000°C. Considering these two characteristics, Thermosphere is originated from the Greek word ‘thermo’ meaning ‘heat’. Due to the heat generated in this layer, temperatures here can rise to about 2000°C and is highly dependent on solar activity. 

What is the Thermosphere composed of?

Different types of atoms and molecules are thoroughly mixed together by the turbulence in the atmosphere below the Thermosphere. Based on the chemical elements they contain, the gas particles collide so infrequently that the gases become somewhat separated in the Thermosphere and above. The main components of air in the upper Thermosphere are atomic oxygen (O), atomic nitrogen (N) and Helium (He). Also, the molecules break apart in the Thermosphere due to the energetic ultraviolet and X-ray photons from the Sun.

What is an Ionosphere?

Most of the scientists consider Ionosphere as an extension to the Thermosphere. Hence, technically Ionosphere is not another atmospheric layer. About less than 0.1% of the total mass of the earth’s atmosphere is Ionosphere. It is called Ionosphere as the upper atmosphere is ionized by solar radiation. In simple words, the Sun’s energy is so strong at this level that the molecules break apart. Temperatures in the Ionosphere, increases with altitude. 

What are the regions of Ionosphere?

Home to auroras, below mentions regions of Ionosphere enable long distance radio communication by reflecting the radio waves back to earth. These regions are broken on the basis of the wavelength of solar radiation that gets absorbed in it. They are:

  • The D region: Though it absorbs the most energetic radiation, hard x-rays, it is the lowest in altitude. It includes the ionization that occurs below 90 km and does not have a definite starting and stopping point.
  • E region: It absorbs soft x-rays and peaks at about 105 km.
  • F region: Starting at about 105 km, it has a maximum of around 600 km. Extreme Ultra-violet radiation is absorbed here and is hence the highest of all regions. 
Why is the Thermosphere important?

Thermosphere is important because:

  • The Thermosphere protects the earth and makes space exploration and modern forms of communication possible.
  • It supports life on the planet.
  • It protects the earth from the severely cold temperatures of space by recycling water, absorbing the sun’s energy and creating a moderate temperature.
  • A large portion of the ultraviolet and x-ray radiation is put off by the sun and is absorbed by the Thermosphere.

Thermosphere consists of five layers of gases, especially oxygen and nitrogen. 

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