Sudden ionospheric disturbance

In years with increased solar activity may in effusive eruptions on the sun, called solar flares or flares, lead to an increased radiation intensity in the X-ray range. This applies electromagnetic energy to the atmosphere, then the X-rays to the layer D of the ionosphere, ie at altitudes of about 70 km above the earth's surface, penetrate and ionize these strong, which is referred to as Mögel - Dellinger effect. Was discovered the effect in the year 1930 by the German Hans Mögel. 1935, the American John Howard Dellinger U.S. Standardization Office ( National Bureau of Standards ) has presented him.

The effect only occurs on the dayside of the Earth and attenuates frequencies up to about 300 MHz. The increased plasma density increases the ability of the D- layer to absorb short-wave - to their complete extinction. This can lead to a partial or complete loss of all short -wave radio links across the sky wave. The phenomenon may take a few minutes to several hours. It is known in German-speaking countries under the name Dead quarter of an hour.

In the English -speaking world it is called short wave fadeout. This extreme case of total annihilation of all short-wave part of the upper group of Ionosphärenstörungen of sudden ionospheric disturbance Sudden English (SID).