Mögel-Dellinger effect

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The propagation conditions for a flare (red rays)
compared to those of a normal, calm ionosphere (blue ray):
The increased electron density leads to increased attenuation in the D-layer (dull red) up to total signal loss or unusual refraction at the E- Layer.

The Mögel-Dellinger effect describes a brief failure of primarily short-wave connections and their propagation via the sky wave , triggered by solar flares . The effect was discovered around 1930 by the German Hans Mögel . 1935 has made him the American John Howard Dellinger US Standardization Office (then English National Bureau of Standards NBS, now National Institute of Standards and Technology NIST) presented.

General

In years with increased solar activity , strong solar flares or flares can lead to increased radiation intensity in the X-ray range . If this high-energy electromagnetic wave from the eruption on the sun hits the earth's atmosphere , the X-rays can penetrate to the deep D-layer of the ionosphere at heights of approx. 70 km above the earth's surface and ionize them strongly . This ionization and thus the increased plasma density increases the ability of the D-layer to absorb short waves - up to and including their complete extinction.

The Mögel-Dellinger effect only occurs on the day side of the earth and attenuates frequencies up to around 300  MHz . This can lead to a partial or complete failure of all shortwave radio connections via the sky wave . The phenomenon can last from a few minutes to several hours. It is also known in German-speaking countries as the dead quarter hour . In the English-speaking world one speaks of English short wave fadeout .

The extreme case of the total annihilation of all short-wave part of the top group of the sudden Ionosphärenstörungen , English sudden ionospheric disturbance (SID) .

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