Figure 17.
Daily and seasonal variations in ion density.
c. Seasonal Cycle. As the earth tilts on its axis, the sun rays
strike the layers obliquely.
This will cause the northern half of
all layers to be more ionized than the southern half because the
northern hemisphere is tilted away from the sun.
We can also see
that there is a difference in layer height during the winter and
summer.
d. Eleven Year Cycle.
As stated earlier, the sunspot activity
varies over an eleven year period.
During a high sunspot activity,
higher frequencies may be used. Longer distance communication may be
also possible because of the use of higher frequencies.
During low
sunspot activity, lower frequencies must be used and shorter distance
radio circuits can be expected.
e. Twenty-seven Day Cycle.
The sun requires 27 days to rotate
around its axis.
While rotating, sun exposes different sunspot
concentrations.
This variation affects the layers, sometimes making
F2 predictions difficult.
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