Electromagnetic Waves-Layers Of Earth’s Atmosphere-E-Layer

Structure of Atmosphere 

As we know, the earth’s atmosphere is made up of various layers. All these layers are different from each other and have particular traits.

The name of the layers of the atmosphere upwards from the ground is as follows:-

• Troposphere
• Stratosphere
• Mesosphere
• Thermosphere
• Ionosphere
• Exosphere

The exosphere then leads out into interplanetary space.

IONOSPHERE

• The fifth layer of the atmosphere is called the Ionosphere.
• The ionised part of the atmosphere stretches from 48 km to 965 km altitude.
• The Ionosphere is the part of the atmosphere ionised by the sun’s radiation.
• Hence, it is responsible for playing a significant role in atmospheric electricity and forming the inside edge of the magnetosphere.
• It is vital because it propagates radio waves to remote places on the earth’s surface.
• The Ionosphere is essentially a cover of electrons and atoms and electrically charged molecules. These particles surround the earth and are formed as a result of ultraviolet rays from the sun.
• The free electrons that exist in the ionosphere are responsible for the propagation of the radio waves.
• The ionisation of the particles in this layer depends mainly on solar activity.

Features of the Ionosphere

The Ionosphere has the following features: –

• It houses all the charged particles present in the atmosphere. In this layer, all the gases present are heated to such an extent that they end up losing electrons, creating a vast expanse of charged particles.
• It is the outermost layer of the earth that is nearest to space. The ionosphere, along with the neutral upper atmosphere, forms a link between Earth’s lower atmosphere and space.
• The ionosphere is dynamic. It changes from day to night because it is created when particles are ionised by the Sun’s energy. The ionosphere gets thinner at night as previously ionised particles loosen and rearrange back into neutral particles. However, there are more unpredictable changes caused by factors both from Earth and from space, that make it difficult to predict what the ionosphere will be like at any given time.
• The Ionosphere is the home for all the satellites. This space boundary is where many of our Earth-orbiting satellites, including the International Space Station, are situated. That means these satellites can be affected by the ionosphere’s constantly changing conditions, such as sudden surges of charged particles, which increase drag on satellites and reduce the time for which they can orbit the earth.
• As the Ionosphere is important for navigation and communication systems, they provide a path for the radio and GPS systems.
• This means that any change in the composition of the Ionosphere leads to the disruption of these signals.
• Weather phenomena like hurricanes also influence the Ionosphere.

Layers of the Ionosphere

• There exist several layers within the Ionosphere, which lead to different effects on radio waves and radio signals.
• These layers are called the D, E, and F layers.
• These layers are differentiated based on the levels of ionisation.
• The F layer is the only layer with significant ionisation at night, with ionisation in the E and D layers being extremely low. The D and E layers become much more ionised during the day, as does the F layer, which develops another weaker region of ionisation known as the F1 layer.
• Here we know more about the E layer of the Atmosphere.

E layer of the Ionosphere

• The E layer of the Ionosphere is also called the Kennelly–Heaviside layer.
• It is named after Arthur E. Kennelly and Oliver Heaviside.
• This layer contains gases in an ionised form that stretch at about 90 to 150 kilometres in height from the earth’s surface.
• It is the area where medium-frequency radio waves are reflected.
• This layer causes the radio waves that are radiated into the sky to return to the horizon.
• This “skywave” or “skip” propagation technique has been used for long-distance radio communication, up to transcontinental distances, since the 1920s
• This layer is responsible for the refraction of the radio signals instead of reducing them so that they return to the earth.
• Thus, it appears that they have been reflected from the earth.
• The air density is much lower at altitudes where the E layer or E region exists than in the D region. This leads to fewer collisions when the free electrons are excited and vibrate due to radio signals. 
• As a result, the E layer or E region behaves slightly differently. The radio signal sets the electrons in motion again, but they re-radiate it.
• The signal is refracted away from the area of electrons with a higher density as it travels in an area where the electrons’ density increases. This refraction is usually enough to bend the HF signals back to earth.
• The level of ionisation in the E region falls faster after the dark as ions and electrons recombine and virtually disappear at night, similar to the D region.
• The level of ionisation, like that of the D region, falls pretty fast at night time since electrically charged particles recombine and almost vanish at night.
• However, residual nighttime ionisation in the lower E region causes some absorption of signals in the lower HF portion of the radio communications spectrum.
• The ionisation of the E layer comes from the different radiations produced by the sun.
• The soft X-rays produce significant ionisation, with some contribution from the extreme ultraviolet rays.

Conclusion

The E layer is a part of the Ionosphere that is ionised through the UV rays of the Sun. It is important as it plays a pivotal role in electromagnetic flow and has practical importance due to its influence on radio propagation to far-off places on the earth.