The ionosphere consists of the following ionized layers:
D-Layer – 60-99 km
E-Layer-90-130 km Sporadic
E-layer – 110 km
E2-layer- 150 km
F1 – layer
F2-layer – 150-380 km
G-layer – 400 km and above.
The D-layer reflects low-frequency radio waves, but absorbs medium-and high- frequency waves. Being closely associated with solar radiation, it disappears as soon as the sun sets. During increased sun spot activity all medium-and high- frequency radio waves stop.
The E-layer is also called the Kennelly-Heaviside layer. It reflects the medium-and high-frequency radio waves. It is much better defined than the D-layer. It is produced by ultraviolet photons from the sun interacting with nitrogen and nitrogen molecules. This layer also does not exist at night.
This layer occurs under special circumstances. It is believed that this sporadic layer is caused by meteors and by the same processes that cause aurora lights. This region is often characterized by high-velocity winds. It affects very high-frequency radio waves.
This region is found above the E-layer and sporadic E-layer. It is produced by ultraviolet photons acting upon oxygen molecules. It appears in day time and vanishes at the sunset.
There is another reflecting layer above the different layers of E-region. There are two sub-layers in this region: F1 and F2. These two sub-layers are collectively known as the “Appleton layer”.
The F1 appears during the day, but disappears at night. This layer is especially important in long-distance radio communication. It reflects the medium-and high-frequency radio waves.
Like the F1-layer this layer is very important in long-distance radio transmission. This layer is characterized by diurnal as well as seasonal variability. It appears as directly related to sunspot activity. Its maximum development occurs shortly after local noon and during the middle of winter.
This reflecting layer is found above the F2-layer. Its existence came to be known as a result of the latest exploration carried into the upper part of the atmosphere.
It is most probably present much of the time, but it may not be detectable since the F-layer reflects all waves reflected by this layer. Because of the interaction of ultraviolet photons with nitrogen atoms, free electrons are produced in the G-layer.