Hi, stemians. It feels awesome to be back writing STEM after a while. It is a new dawn for me as I will begin to write on topics related to my research area, and link it up with my findings eventually. I am working on the perturbation introduced by eclipse event in the dynamics and composition of the ionosphere. I seek to reveal the dynamical complexixity, as well as to model the behavior of the ionosphere before, during and after eclipse events. I will start building from the basics and gradually painting the bigger picture. Let’s get right to it, shall we?
Many people wonder why radio communications, especially over long distances, is possible. I remember at the very advent of GSM network in my country, some people were of the opinion that it is witchcraft and some even try to distance themselves from using the technology.
Is it really witchcraft?
As it is said information is power, what you refuse to find out you will remain a slave to. To answer the above question, it is important to know that whatever you seek, you will find. This applies to anything and is also the case with radio communication that men eventually invented. It is not in any way witchcraft (witchcraft is simply an unexplained science) and it is made possible primarily by the layer of the atmosphere called the ionosphere.
It was James Clark Maxwell who first points the attention of the world to the possibility of using electromagnetic wave in space for radio communication. In his electromagnetic field theory stated in 1873, Maxwell explains that electromagnetic waves also have properties of light i.e. they can be reflected, refracted or even absorbed. Most importantly also is the fact that light itself is an electromagnetic wave.
It was Sir Edward Appleton who first discovered that radio waves were transmitted around the world after being reflected back from the ionosphere[1]. This is made possible by the large concentrations of charged particles (ions) and free electrons present in this region of the atmosphere.
However, it would be Guglielmo Marconi that would first send a signal to a location a few km away through wireless telegraph [2]. The big question then was, can telegraph provide an effective means of sending signals over longer distances and across the continent? So, researcher began the development of radio communication and gradually Morse code was developed and in time we are where we are today in radio communication.
The Earth’s atmosphere has five primary layers which are the troposphere (0-12km), the stratosphere (12-50km), the mesosphere (50-80km), and the thermosphere (80-700km).
The ionosphere falls in the upper part of the Earth’s atmosphere which is rich in ions (charged particles). Other parts of the atmosphere also contain charged particles but not as much as the ionosphere. This layer can be found between the thermosphere, the exosphere and it eventually merged with the magnetosphere (outer space region).
The ions and free electrons present in the ionosphere aids radio communication and they are made available majorly by solar radiation. So, it will be right to say that the ionosphere owes its existence to the Sun and once the Sun is no more, it will be the end of many things including our whole planet.
[image credits: wikipedia commons under the Creative Commons Attribution-Share Alike 3.0 Unported license]
During the day, the solar corona produces a constant stream of UV and X-ray which travels to the earth causing ionization in the ionosphere. Simultaneously, a process called recombination occur which entails electron capturing by positive ions. The balance between these two processes determines the level of ionization present in the ionosphere at any given time. If photoionization is more than recombination, then you can be sure to have more ions present for radio communication.
Also, the amount of ionization depends on the amount of solar radiation received. The solar radiation received depends on the sunspot cycle. The more the sunspot, the more the level of ionization in the ionosphere. Thus, there is diurnal effect and seasonal effect. Also, ionization varies with geographical locations i.e. polar regions, aural region, equatorial region, zones, mid-latitude where the intensity of sunlight received varies. This implies that only part of the ionosphere is being ionized by the Sun at any given time.
WHAT IONIZES THE IONOSPHERE AT NIGHT?
When the Sun is no longer in the night skies, the duties of ionization falls to cosmic rays emanating from various sources throughout our galaxy and the universe. It can be from rotating neutron stars, or supernovae, or radio galaxies, or even quasars and black holes. Even though the ionization produced by cosmic rays is not as strong as that from solar UV and X-ray, it is just sufficient to ensures the continuous reflection of radio signals at night.
LAYERS OF THE IONOSPHERE
[image credits: Wikimedia, Public Domain]
IMPORTANCE OF THE IONOSPHERE TO MAN
[image credits: wikipedia commons under the Creative Commons Attribution-Share Alike 2.5 Generic license]
The more the number of free electrons available (density), the higher the frequencies that can be reflected. At any time, the number of free electrons present in the ionosphere is sufficient to influence radio propagation between locations on the Earth. For VLF (Very Low Frequency) signals, the ionosphere in conjunction with the ground produces a waveguide through which the signal can bounce and curve, making its way around the Earth. The ionosphere does not allow the use of the same frequency throughout the year or even 24hours due to its instability. That is why radio communication signals that travel to the ionosphere are varied by the communication gadgets.
The ionosphere enables radio wave propagation (radio signal) that is used in broadcasting, ship and aircraft communication, telecommunication and navigation by ensuring that signals are reflected back to the receivers, though, its efficiency depends on the frequency of the transmitted signal. This is a critical point as the performance of the ionosphere is markedly different during the day and at night.
However, these variations are somewhat regular, which may also be predicted. (I believe there are some non-linearity embedded which is why I am undergoing a research to reveal the non-linearity in the dynamics of the ionosphere revealed possibly during eclipse events). These predictions have enhanced the planning of radio services over the decades.
When radio signals travels from the Earth or satellite into the ionosphere, some amount of energy carried by the radio wave is transferred to the free electrons and ions of the ionosphere, causing the oscillation of these free electrons and ions at the same frequency as that of the radio signal. This, in turn, leads to the attenuation of the radio wave signal when passing through the ionosphere.
This attenuation is more in the lower regions especially the D region where neutral particle density is more as compared with upper regions characterized by more free electrons. Furthermore, the collision frequency of the electrons with the neutral particles is inversely proportional to the square of the frequency of the radio waves.
In effect, attenuation is greater as the frequency is lower or wavelength is longer. Consequently, when radio signals pass through upper regions of the ionosphere, the signals undergo little loss of strength.
RADIO WAVE
[image credits: Wikimedia, Public Domain]
Low frequency/Medium frequency (LF/MF)
High frequency (HF)
Very high frequency/Ultra high frequency (VHF/UHF)
Super high frequency (SHF)
Radio wave travels at the speed of light (300, 000,000m/s) given by the relation ∁=fλ Where C is the speed, f is the frequency and λ is the wavelength. So high frequency implies low wavelength and vice versa. Electromagnetic waves within a range of 30 MHz can return to Earth after being bent (reflected) by the ionosphere. Thus, apart from times when solar eruptions are strong, radio waves that are over 30 MHz frequency is not reflected and can penetrate the atmosphere (ionosphere) and reach outer space, hence making communication between outer space and the Earth achievable.
Therefore, radio waves of over 30 MHz are used for intercontinental communications via communication satellites.
Artificial satellites are built to reproduce the effects experienced in the ionosphere, their natural brother, and they, therefore, act the same way (as a reflector), as the ionosphere for frequency above 30MHz.
Radio waves originating from the Earth are reflected by these satellites if they fall within their range (coverage area).despite being produced with the highest technology existing, manmade satellite faced a limitation in their coverage area. Another notable disadvantage is that they are very expensive to produce and can last only for approximately 25 years.
Thanks to the wide coverage of the ionosphere (covering the entire planet), radio frequency lower than 30 MHz can be transmitted across the globe. Due to the natural occurrence of the ionosphere, it requires no maintenance, no supply of energy or gases and is a permanent region of the atmosphere.
CONCLUSION
Our curiosity has made us to discover more of the embedded properties of the universe, and the ionosphere is one. This has also assisted us to better understanding the universe. The ionosphere had made modern communication possible, but its effeciency and dynamics is being affected by so many factor such as scintillation, eclipse events, geomagnetic storm etc.We need to understand how these factors influence our dear ionosphere.The knowledge of the dynamics of the ionosphere is one that is unending and as long as humanity exists, more study will be carried out to further evolve a more robust understanding of the ionosphere, and indeed the entire universe.
REFERENCES
- Wikipedia:history of radio
- Ionosphere and radio communication
- Sir Edward Appleton and the propagation of radio waves
- The importance of ionosphere in radio communication
- Radio waves and the ionosphere
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