(1) Eruptions on the surface of the sun shoot hot gases from
its surface up to a half million miles away.
Spots of intense
ultraviolet radiation are another disturbance noted. These spots are
referred to as sunspots.
(2) The number of sunspots vary from year to year. The minimum
to maximum sunspot cycle takes about 11.1 years.
During periods of
high sunspot activity, higher frequencies are usable.
During low
sunspot activity, lower frequencies must be used.
Figure 11.
Sunspots.
(3) Dellinger fade.
When the sun produces bright visible
flares, the effect is felt immediately in the various ionospheric
layers.
Absorption of most radio frequencies is noted during this
period. It is called the Dellinger fade. The lower frequencies are
affected to a lesser degree.
3.
Ionosphere Layers or Regions.
There are four layers in the
They called the D, E, F1, and F2 layers.
All four
layers are present during the daytime.
At night, the F1 and F2
layers thin out and tend to merge into one layer - the F layer. The
D and E layers disappear at night.
These layers have less
ionization. After the sun sets, recombination occurs and the layers
disappear.
The number of layers, their height, and level of
ionization fluctuates.
The ionization changes hour by hour, day by
day, month by month, season by season, and year by year.
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