Which of the following layers makes radio transmission possible? (CSS 2009 General Science & Ability Paper)

Troposphere
Ionosphere
Mesosphere
Stratosphere

The ionosphere is the ionized part of Earth’s upper atmosphere that extends from about 80 to 600 km above sea level. It’s a region within the thermosphere filled with charged particles that play a crucial role in radio communication by reflecting radio waves back to Earth. It also contributes to the occurrence of auroras and is ionized by solar radiation. The ionosphere has historically been divided into regions (D, E, and F) , with the term “layer” referring to the ionization within a region.

Bouncing radio signals off the Ionosphere is what allows radio signals to reach places all over the world. Overall, the ionosphere’s layers interact with radio waves based on their frequencies and the time of day, with higher layers generally supporting long-distance HF communication and lower layers absorbing or reflecting lower frequency waves.

  • Ionization is the process by which ions are formed by gain or loss of an electron from an atom or molecule.
  • In 1901, Marconi transmitted a signal between Europe and North America and showed that it had to bounce off an electrically conducting layer at about 100 km altitude. It became apparent that the radio waves followed the earth’s curvature.
  • At high latitudes there is another source of ionisation called the aurora. The aurora is a display of light caused by electrons and protons striking the atmosphere at high speed. The particles come from the magnetosphere and spiral down the magnetic field lines of the Earth. These particles produce a spectacular array of light, and when they strike the atmosphere they also produce ionisation.

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