A burst of X rays was observed at balloon altitude over Alaska with the onset of a sudden commencement geomagnetic storm at 0146 UT on June 27, 1960. The electron bombardment of the upper atmosphere that gave rise to the X rays occurred on a large scale, ionospheric absorption coincident with the X‐ray burst being observed by riometers in Alaska, Sweden, and Norway.

Cosmic noise absorption coinciding with the sudden commencement of geomagnetic storms has been studied for 71 SC events from the data recorded at 25 riometer stations at or near the auroral zone during the period July 1958‐December 1960. The greatest absorption was registered at stations near the central line of the auroral zone. The effect was observed simultaneously on the day and on the night side of the earth. This type of absorption was earlier found to be associated with bremsstrahlung X rays created by electrons entering the lower ionosphere. The source of these electrons has not been definitely established by the present study. Although the data tends to favor a source outside the earth's magnetosphere, no definite conclusion is possible because of the present uncertainties concerning the trapped radiation belts.

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