Layers of Earth’s Atmosphere – F1 Layer

As the name suggests, an electromagnetic wave consists of an electric field and a magnetic field that is perpendicular to each other. It is neutral. Hence, when it passes through an electric or magnetic field, it does not deviate from its path. Mechanical waves like sound waves or water waves require a medium to flow. However, electromagnetic waves can travel without any medium. 

Learn how the propagation of UV radiation (an electromagnetic wave) changes through the various layers of the atmosphere. Interestingly, such a change in layers of atmosphere helps the transmission of all radio waves (another form of electromagnetic wave) on Earth’s surface. 

Forms of electromagnetic waves & their usage:

There are seven different types of electromagnetic waves that form the electromagnetic spectrum. Like any other waves, these waves are characterised by their amplitude (or strength), wavelength (or distance), and frequency. The frequency of electromagnetic waves in the spectrum ranges between 104 to 1024 Hertz.

• Visible Light: Yes, visible light also comes under electromagnetic waves. We can see this beautiful world around us because of the strong visible light sent to Earth by the sun. 
• X-ray: This is widely useful in the medical field to capture images of internal organs of the human body. 
• Microwaves: Popular kitchen appliances (microwave ovens) use these electromagnetic waves for cooking food. It is also used in radar to locate distant objects. 
• Infrared light: This electromagnetic radiation gathers scientific research about the stars situated far away from Earth. 
• Ultraviolet radiation: This has an ionising effect. It has the potential to produce free radicals on our skin surface. Sunburns and suntan are signs of skin damage caused by the sun’s UV rays. 
• Gamma rays: This can be life-threatening for living creatures. It has very limited use and is to be handled in a controlled manner. 
• Radio Waves: This is widely used for communication. Starting from television to GPS network to cellular network can function normally due to proper transmission of radio waves from one place to another. The ionosphere layer in Earth’s atmosphere plays a major role in transmitting radio waves. 

Layers of Earth’s Atmosphere:

We all know the surface of Earth is covered by a thick blanket of a mixture of gases called the atmosphere. Atmospheric gases include oxygen, nitrogen, carbon dioxide, argon, etc., and some water vapour. There are five distinct layers of Earth’s atmosphere:

• Troposphere:

This is nearest to Earth’s surface. It stretches up to 17 km from the surface of Earth at the equator. The density of the air is highest in this layer. It holds almost 75% of the total atmospheric gases. All the changes in weather conditions take place here. 

• Stratosphere:

This layer lies just above the troposphere. The ozone layer that protects us from the harmful ultraviolet radiation emitted by the sun can be found here. 

• Mesosphere:

It lies in between the stratosphere and the thermosphere. Combustion of the meteors, which we see as a sudden flash of light during the night, happens in this region. 

• Thermosphere:

The ionosphere is present in this layer of the atmosphere.

• Exosphere:

This is the topmost layer of the atmosphere. Air density is extremely low in this layer.  

Structure and Composition of the Ionosphere: 

The ionosphere lies between 60 – 300 km from Earth’s surface. The ionosphere plays a crucial role in propagating radio signals on Earth’s surface. This is possible because of the availability of many free ions and electrons. 

When atoms and molecules of the atmospheric gases present in the ionosphere get hit by the powerful ultraviolet radiation of the sun, electrons are released from them. In other words, those atoms and molecules split up to form ions and electrons. This process is called photo-ionisation. 

When high-frequency radio waves are sent out from Earth into the sky, the waves strike this ionised layer. Many ionised particles present here reflect these radio waves to Earth’s surface at a deviated angle. This deflection of radio waves makes long-distance communication possible.

Regions of Ionosphere:

The ionosphere can be segregated into three different regions. Their contribution towards radio propagation is as mentioned below.

D-region:

This is the lowermost portion of the ionosphere. Radio signals mostly pass through this region uninterrupted. 

E-region:

Marconi’s first-ever transmission of radio signals for wireless communication happened in this region. 

F-region:

The density of negative ions is quite high in the F-region. Maximum transmission of radio signals happens from this region. The F-region tends to get split into two different layers, namely the F1 and F2.

Role of F1 Layer in Radio Transmission

The F-region of the ionosphere is often referred to as the Appleton–Barnett layer. It is named after two renowned scientists – English physicist Edward Appleton and New Zealand physicist Miles Barnett. 

Edward Appleton is credited for his discovery of the existence of the ionosphere in Earth’s atmosphere. Miles Barnett is credited for his extensive studies on the propagation of radio waves.  

The F1 layer exists between 130-220 km above sea level. It covers the lower range of the F region. It is often termed as a secondary layer of the F-region. This is because it becomes non-existent during the night. It can be found only during the daytime. 

The disappearing act of the F1 layer:

Let’s understand the disappearing act of the F1 layer. The neutral atoms and molecules present in the F1 layer become charged particles under the sun’s ionising ultraviolet radiation. 

These particles can hold on to their ionised state as long as the sun’s UV rays are available. After sunset, in the absence of sunlight, the ions and electrons tend to combine with their oppositely charged counterparts. As a result, these particles become neutral. The neutral particles thus formed lose their ability to transmit radio signals. They regain their capacity to transmit radio signals after sunrise the next morning.

Hence, we can say the F1 layer of the ionosphere is not a reliable component for transmitting radio waves. On the other hand, the F2 layer is available with its high electron density and can contribute towards radio transmission all day and night. 

Conclusion:

To summarise the topic, Electromagnetic Waves –Layers of Earth’s Atmosphere – F1 Layer, here is some important point you should remember: 

• There are seven different forms of electromagnetic waves, including radio waves. 
• In this era of widespread communication, radio waves are most widely used in various communication channels. It can be television, GPS or mobile phone. 
• There are five distinct layers in Earth’s atmosphere. 
• The ionosphere, present in the thermosphere layer, is mainly responsible for all forms of radio communications. 
• The F1 layer is the second layer of the ionosphere’s F-region, and it participates in radio communication only during the daytime.