What and where is the Earth's ionosphere?
The ionosphere is a region in the Earth's atmosphere that has an effect on the transmission of radio waves. It has a high concentration of ions - electrically charged particles.
The ionosphere allows the transmission of radio signals to follow the curve of the Earth's surface.
The ionosphere begins at a height of about 50 kilometres above the Earth's surface but is most distinct at altitudes of above 80 km.
It has three layers. The lowest is called the D region and is most strongly ionised during the day. It reduces shortwave and broadcast- band radio signals but this effect largely disappears with nightfall.
The E layer, extending from 90 to 140 km, is a region of ionised molecules and strong electric currents.