Figure 12. Layers of the ionosphere.
a. D Layer.
The D layer is approximately 30 to 55 miles above
the earth. This layer has the least ionization and therefore has the
lease effect on radio frequencies.
It is present during the day
only. The height varies over the eleven year sunspot cycle. The D
layer is approximately 6 miles thick.
b. E Layer.
The E layer is approximately 55 to 90 miles above
the earth.
The E layer reflects radio frequencies up to about 20
MHz. The maximum one hop range of the E layer is 1,500 miles. This
layer is present only during the day. The height of the layer varies
during the eleven year sunspot cycle.
The E layer is approximately
15 miles thick.
c. F Layer. The F layer is from 90 to 240 miles above the earth.
The F layer is present only at night. This layer is created when the
F1 and F2 merge. Because it is the most ionized, recombination takes
place more slowly. The height varies over the course of the eleven
year sunspot cycle.
d. F1 and F2 Layers. During the daylight hours, the F1 layer has
a height of approximately 90 miles and is approximately 12 miles
thick. The F2 layer has a height of approximately 160 to 220 miles
and is approximately 15 miles thick. The F2 layer, being the closest
to the sun, has the most ionization.
The height of both layers
varies over the eleven year cycle of sunspot activity.
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