Explanation: The transmitted signal travels into the upper atmosphere where it is reflected back to earth due to the presence of layers called as ionosphere in the upper atmosphere. The D layer is the lowest and it exist at a height of about 70 Km from the earth surface. The E layer existing at an approximate height of 100 Km. The E layer also almost disappears at night due to recombination of ions and molecules. The E layer is a thin layer of very high ionization density, sometimes making an appearance with the E layer. The F1 layer exist at a height of 180Km in daytime & combines with F2 layer at night its daytime thickness is almost 20Km.
The Ionosphere is the upper portion of the atmosphere. The ultra violet radiation from the sun will ionize the upper layer of the atmosphere. Due to ionization these part of the atmosphere becomes electrically charged. In this layer free electrons and positive and negative ions are present and hence this layer of ions is known as ionosphere. There are four layers: D, E, F1 and F2.
Properties of layers of ionosphere:- 1. D Layer: It is lowest layer at a height of 70 kms with thickness 10 km. The ionization density is maximum at noon and disappears at night. 2. E Layer: It is the next layer at a height of 100 kms with thickness 25 km. The layer disappears at night due to recombination of ions and molecules. 3. F1Layer: It is the next layer at a height of 180 kms with thickness 20 km. It provides more absorption for HF waves. 4. F2Layer: It is the next layer at a height of 250-400 kms with thickness 200 km. It is having highest electron density of all layers, due to this F2 layer remains present at night time.