Sudden Disturbances of the Ionosphere

The phenomenon described in this paper is the occurrence of a very sudden change in ionization of a portion of the ionosphere. It manifests itself by the complete fading out of high-frequency radio transmission for a period of a few minutes to an hour or more, and by perturbations of terrestrial magnetism and earth currents. The effect was discovered in 1935, and found to occur simultaneously everywhere throughout the illuminated half of the globe but not in the night half. The results of a world-wide investigation of the phenomenon which followed this discovery are presented in this paper. The radio and magnetic effects have been shown to be of a distinct type, quite different from previously known vagaries in these fields. They are of maximum intensity in that region of the earth where the sun´s radiation is perpendicular. Many of the occurrences are simultaneous with great eruptions on the sun. Such eruptions emit vast quantities of ultraviolet light. These radiations are sometimes of such frequencies as to cause intense ionization of part of the ionosphere below the E layer. This sudden ionization causes the radio and other perturbations. Their characteristics are explained. Study of this effect is leading to new understanding of the nature of the ionosphere, the processes of radio wave transmission, the mechanisms of terrestrial magnetism, and the phenomena occurring in the sun.