c. Sudden Ionospheric Disturbance or Dellinger Fade. Ionization
from a violent solar eruption travels down to the D layer.
This
causes an almost total absorption of all frequencies, above 1 MHz.
This disturbance is called SID or Dellinger fade.
This blackout of
radio communication may last from a few minutes to several hours.
d. Ionospheric Storms.
An ionospheric storm is caused by a
severe disturbance of the ionospheric layers.
The levels of
ionization of the layers thin out, making reflections frequencies
above 1.5 MHz difficult.
Lower working frequencies are in order.
These storms may last several hours to several days.
These storms
are caused by particle radiation from the sun. The storms will start
normally after a sunspot group crosses the center of the sun.
Table 5.
Irregular Variations of Ionosphere.
31
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